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I am entranced by cause and effect.

This probably has some direct bearing on my chosen career as a storyteller. The real world is devoid of narratives, after all. Narratives are just a thing that our brains do with facts in order to draw a line around the incomprehensible largeness of reality and wrestle it into something learnable and manipulable. Existence is devoid of plot, theme, and most of all moral.

And yet I can still be struck dumb when two facts I knew, but never really considered before, snap into synthesis. The a-hah moment is incredibly powerful.

Consider: wildfires appear to have been more common and more widespread during the Cretaceous period. Consider also, that oxygen levels may have been considerably higher--as much as 35%, by some sampling techniques, as opposed to today's paltry 21%.

(I've found a few references to a 2013 study that seems to indicate that Triassic oxygen levels may have been even lower, but that's a whole different era of the same eon. (Or aeon, if you prefer.))

I knew these two facts in isolation for some time. But at some point they clicked into place for me, and I realized that each implies the other.


Or more precisely, a-hah!


One of my great joys as a writer lies in teaching. I have been privileged to teach at several workshops over the years, and one of the things that I try hardest to teach my students is that the most powerful emotional effect a story can have on the reader is the one summoned when the reader figures things out for themself. Where the writer provides the information--the clues--and the reader puts them together and figures out how something works.

I also teach them that one of the coolest tricks to pull in worldbuilding is to imply things. An oaken chair implies cold, temperate forests harvested for timber. Shipping implies trade. And so forth.

Of course, it's also the trickiest trick to pull off, because the necessary clue level varies from reader to reader, and nobody likes to feel led by the nose, and some readers don't actually want to figure things out: they just want to be told.

The deep irony is, of course, that while I can tell an apprentice writer this, they won't really understand it until they figure it out for themself.

I love unreliable narrators. I love those moments when as a reader, I realize something slightly before the narrative makes it plain. I love the little neurological endorphin cookie that my brain feeds me: "Congratulations! You learned something! Perhaps you'll live another day!"

This is also how inspiration works, incidentally: you stack up disparate things against one another until suddenly, your brain arranges a connection. It makes a pattern. It creates a narrative, where no narrative was before.


So it turns out that one can use fossil carbon beds as a predictor of prehistoric atmospheric oxygen levels.

One thing is implied in another. A-hah.



Yup! And the implication/reward thing in the reader's head leads on to the proposal by a critic of the field (I think it was John Clute: I may be misremembering) that one of the key differences between SF (or fantasy) and mainstream fiction -- a key difference which throws many untrained readers -- is that in SF/F, the world is a character, and decoding the personality of the world -- how it works and how it responds to stimuli -- is a key part of the reading experience.

(Which also leads to the common plaint from non-SF readers, "but you can just make anything up, can't you?" -- Which is almost exactly false, and is a common reason why authors from a non-genre background (by which I mean, mainstream authors who haven't read widely in the field) often fall flat on their faces the first time they try and write SF or fantasy.)


"on SF/F, the world is a character"

Quite. A few mainstream authors have that ability to make their setting a rich and memorable character, and I wonder how many SF fans have read Len Deighton's cold war thrillers (Funeral in Berlin especially). The divided city and its frozen moment in history will stay with you, long after you've forgoten the human characters.

Recommended example of 'mainstream' world-building: 'Goodbye Mickey Mouse'. Underrated, but utterly immersive and you will emerge from it as if you'd lived in wartime Britain; years later you will realise how different a country it was, and that the wartime generation are very, very different people to us.

And yes, the author does it quietly: a detail here, and a character's reaction there, that imply the world as much as pages could describe it.

Which other 'mundane' authors do you think have 'got' worldbuilding?

And who do you recommend as the SF/F masterclass in worldbuilding?


Which other 'mundane' authors do you think have 'got' worldbuilding?

I don't normally go for detective stories but enjoyed the Brother Cadfael books by Ellis Peters which did a very good job of building the background of the Anarchy and a land where the Norman invasion had only just passed from living memory. I'd include Dorothy Sayers Wimseys and most of P G Wodehouse but they were immersed in the background they were writing about.

On the other hand, built worlds rarely approach the alien-ness of the Chinese society that forms the background of "Outlaws of the Marsh" and "The Three Kingdoms".


Elizabeth, more fundamentally, I think we have different understandings of the "unreliable narrator". I take that as meaning that, even if they are not lying to you, their understanding of $thing (include technologies, plot points, other characters...) is not necessarily correct, rather than that you can arrive at a realisation that "the butler dunnit" before the narrator does.

As to the question that Vulch answered, I'm also going to nominate a historic whodunnit (his is a good choice, but if you like one of our nominations, you shold try the other): Peter Tremaine's "Sister Fidelma" books, set mostly in Ireland in the period immediately prior to the Synod of Whitby.


""on SF/F, the world is a character""

Indeed. And if's not a believable, consistent world, that's as bad as a character whose motivations and personality are inconsistent. And just as much a turn off to a reader, especially a deep reader of the genre.


Charlie, I agree completely. The game in mainstream fiction is figuring out why people do what they do. The game in our genre is figuring out why the world does what it does.

These are not, of course, mutually exclusive...


Which other 'mundane' authors do you think have 'got' worldbuilding?

Patrick O'Brian's books come to mind. The ships and world of napolionic naval warfare are the bedrock of the series.


Huh. I think OGH in 1 just nailed why I read genre fiction and not mainstream fiction. In genre fiction, I have something to figure out, and there's a process of learning stuff about the setting and trying to put it into place.

If I don't get that in my fiction, I get bored. It would explain why I can read historical fiction and mystery, thought I don't often.


Peter Tremaine's "Sister Fidelma" books

Ta. Hmm, "Tremayne" for anyone else wandering over to a large South American river for a search. Anthology 1 now sitting in my basket waiting for me to find another £3.71 for the free postage...


Kipling, of course.

He didn't have to build the world you see in, for instance, Kim, but he has to describe it without smothering the story. And India is definitely a character.


My apologies; I should have done a search instead of just using the usual Cornish spelling. Mea culpa.


My time at secondary school just across the border had me as a member of Tremaine House so that's the way I'd have spelt it as well.


This strikes me as "huge" since I first read about it (in "The Invention of Air" or another book about early days of science.)

The 60-million-year-long Carboniferous period—when the bulk of the world's coal deposits were laid down and atmospheric CO2 levels declined—ended roughly 300 million years ago WHEN FUNGI EVOLVED THE ABILITY TO BREAK DOWN LIGNIN.

In other words, for 60 million years, trees (whose trunks are made of lignin) COULD NOT ROT.

THAT's where coal comes from. And humanity is burning entire "forests" of coal every year.

(Sorry for the SHOUTING, I don't trust the commenting system to get bold-face right.)


Authors of the study that the Scientific American article was based on, wrote some comments, so those are worth reading, too.


Keith, try HTML tags such as &lti&gt and &ltb&gt. That should get you italic and bold. Use the preview option, though, because getting your markup tags wrong can be embarrassing...


"Which other 'mundane' authors do you think have 'got' worldbuilding?"

Try George Orwell's earlier works. Not the very obvious later book he wrote as a result, but what otherwise are his personal accounts of his life in "Homage to Catalonia," and "The Road To Wigan Pier," They are not fiction but do require worldbuilding and the fact that he is an unreliable source with some (To us) very peculiar attitudes towards what he has seen.

In Homage to Catalonia, the rebel POUM is openly using child soldiers, whereas the Monarchists (Franco) categorically did not because they regarded themselves as the legitimate military. He makes no mention of this point. Some of them subsequently get shot. Orwell has no problem with either their use or the outcome.

In "Wigan Pier," the North of England is discussed in terms of it's poverty. He literally presents their living habits as if they are an alien race, which for much of his readership they effectively were. It's not done to remind the audience that they are human beings underneath, though, it is quietly because of the implied threat that there are way more of them than "you" and they control the industrial base of the Empire's economy.


So, your Aha!! was that one reason the big dinosaurs got along so well, and so large, was extra oxidizer, allowing them to get more energy from less fuel?

The obivious other implication then is, more than the comet/nuclear winter that killed off so many of the dinosaurs, huge - as in large chunks of continent-wide - fires killed so much of the vegetation, and the "winter" kept them from regrowing rapidly, with the result that O2 levels dropped, and that really finished them? It would certainly explain why it took hundreds of thousands, or a couple million years by some accounts, for the die-off.

mark "and those damn dino-hunting alien Hemingways...."


Those are two prevalent theories, yes. I'm not sure any definitive statements can be made.


And if it's not a believable, consistent world, that's as bad as a character whose motivations and personality are inconsistent.

Strongly agree. An example: I read the first few books of the Temeraire series (Dragons! In the Napoleonic Wars!). The characters and dialogue were good, but the world didn't make sense at all. Dragons have coexisted with humans for all of our history, and 18th century Europe still produces a French Revolution and a Napoleon?

Later books showed that the farther away from Europe things got, the more different the world was. Spain never conquered the Inca Empire (so how could the history of Spanish Europe that led to Napoleon (and lots of other things) happen?) Britain never got a toe-hold in India (so how come Arthur Wellesley is important? Where did he learn his trade as a general? Et numerous cetera.)


Always fun to get the real paleontologists in on this. For example, Darren Naish of the blog TetZoo has had some unkind things to say about the fossil record and high or low levels of oxygen in the Mesozoic.

One HUGE problem with the idea of a lot of oxygen in the Cretaceous is that, at the end of the era, there was a rather enormous eruption (the Deccan Traps, the 10th biggest eruption ever), which was pouring a lot of CO2 into the atmosphere for a few hundred thousand years before the Chicxulub bolide ended the Mesozoic. If you think of the Deccan Traps as global warming (a reasonable analog) and the bolide as nuclear winter (also a reasonable analog), you can see that having a nuclear war in the next few centuries would be an incredibly bad thing, far worse than either nuclear war or global warming alone.

That said.

Oaks. Yeah. You know where the highest diversity of oaks in the new world is? MEXICO. There are a huge number of tropical oak trees in Central America, Asia, even montane New Guinea. They tend to be in mountains, up to 12,000 feet in the Himalayas. Oaks do not imply cool temperate at all. That's just our eurocentric biases speaking.


Temeraire is an example of tropes being tools, I think, the trope in this case being consistent worldbuilding. It still works, because the rest of the writing is good, and because of the basic coolness of the concept; if you aren't swayed by the notion of “The Napoleonic Wars WITH DRAGONS!” you'll probably be less inclined to overlook the inconsistencies.

Making it inconsistent runs it slap into one of the issues with alternate timeline fiction: If you really follow through on all the results of the change chaos theory if nothing else dictates that a lot of canon (considering period pieces as history fanfiction) vanishes completely. Applying the appropriate level of change would lead to a world that may as well not be Earth or the 18th century at all, and that's a quite different premise. Not necessarily worse, just different.


Pathetic imitator, actually.

C S Forester & "Hornblower" The original & best


And the little ones survived ... some are twittering outside my windows, right now.


But ... what did you say? They tend to be in mountains, up to 12,000 feet in the Himalayas. Oaks do not imply cool temperate at all. Now think about that. At sea-level, Mexico & New Guinea are tropical, but @ 12 000 feet up, the climate will NOT be "tropical, will it? Cloud-forest perhaps, or montane temperate ... so Oks still require cooler conditions, for slower growth & denser wood - don't they?


On a somewhat related note, there are also some problems with the idea the oxygen content of the atmosphere is kept low by higher incidence of fires; AFAIK the paper cited by Lovelock used wet paper, which is a debatable model for wet plant matter. There might be a paper on that one somewhere, though it might take some time to find it.

actually, my first guess would be higher O2 levels lead to more photorespiration

which would catch up on O2 production, though I don't know if anybody worked this through.

PS: "Lichtatmer" (lterally "light breathers"), a term dervied from the German term for that one, "Lichtatmung" (literally "light breathing"), is also used somewhat humorously for practioners of Breatharianism...


Actually, if the avian pneumatic respiratory system is inherited from early archosaurs (AFAIK there are some indication crocodiles had and lost a similar system), it stand to argue dinosaurs would have coped with little oxygen much better than most other animals...


At sea-level, Mexico & New Guinea are tropical, but @ 12 000 feet up, the climate will NOT be "tropical"

Indeed. There's a vague rule of thumb of the order of every yard up is equivalent to a mile polewards. Kilimanjaro at 19,300-ish feet is 3 degrees south of the equator and (still, just) has a permanent ice cap, as do many of the Andes.


"But you can just make anything up, can't you?"

see also: steampunk

I'm sure there are some good ones in the genre somewhere, but the ones I've tried, it was painfully obvious that the writers saw no difference between engineering and magic.

If you're equating engineering and magic, it helps if the magic is consistent and logical within the story. In the case of the book I incautiously agreed to read last week, approximately 22nd-century genetic engineering technology was developed between 1840 and 1861 in Victorian London, with the rest of medical technology still the same as OTL. Just a sentence or two about how this came about might at least have distracted me from annoyance with the steam-powered flying cars and post-Singularity style Babbage machine brain implants...


Brain implants before the invention of antibiotics? That's... brave...


and Vulch @27

I assume that Heteromeles was thinking in terms of Latitude--north and south of the Tropics, rather than about microclimates.


On tree ecology, there's also the concept of the 'tree line', which is basically the point beyond which trees don't want to grow, due to cold. Go too far upwards, or too far North, and you stop getting trees. Looking at Norway, for example, in the South you have trees in the lowlands and quite a way up the mountain slopes.

As you travel further North, that level gets lower and lower as per your rule of thumb, until by the time you reach Nordkapp, there aren't any even at sea level.

(To be a little more nuanced, give them a suitably sheltered spot, with a sun-facing slope behind them, and some trees will still grow because you have a micro-climate that's sufficiently better to support them. But on open ground, not so much.)


The adiabatic lapse rate is around 3.5oF for every 1,000 feet altitude gain, or 6.4oC decrease per kilometer altitude gained.

No, the bigger point here is about prejudice.

If someone says "oak implies cool temperate," I'm pointing out that oak can easily imply exotic tropical mountains, either in Mexico, Southeast Asia, or Papua. They don't look like northern temperate oaks either (and we're not talking about cloud forests. Those are higher than the oaks).

Oak can also imply chaparral, which comes from a spanish word ("chaparro") for scrub oak. Sadly, scrub oaks are being eliminated in California, and since they're an old growth species, a lot of things are going away with them. There are actually quite a few oaks in California, ranging from the scrubby ones in the chaparral and desert, to the giant valley oaks that used to line the now-channelized rivers of the Central Valley, to the blue oaks that make a bathtub ring around said valley, to the weird deer oak in the northwest mountains that has its closest relatives in Asia.

Oak can also imply what some call "paratropical forests," such as in Louisiana, Florida, and the south. There are plenty of oaks down there, big gothic live oaks festooned with Spanish moss, among many others

So if the only thing oaks make you do is to close your eyes, lie back, and think of England, you're missing most of what oaks are capable of. Heck, Spanish has three words for oak: encino (evergreen oak), roble (deciduous oak), and chaparro (scrub oak). English is depauperate in comparison. Think of how you could use oaks as scene setting if you wrote in Spanish.


Building in aha moments is much like crafting a joke: it has to work on multiple levels. There can be a situation that's funny all on its own. There can be allusions built into it that enhance the mirth but, if missed, don't leave it falling flat. You can risk an obscure reference on a gag line but if the humor value for a major development lies completely in something obscure, a major joke goes to waste. Spell things out too clearly and you insult the reader; be too obscure and you also insult them. Pixar is usually very good about this sort of thing. They are crafting films for all ages. Bright colors and funny voices for small children, simple plots for the older kids, more adult jokes and themes for the parents that will completely go over the heads of the tykes without ruining their enjoyment. When they rewatch the movie with older eyes, they'll find more things to enjoy.

My favorite kind of aha moments are when what looks like a worldbuilding flaw is really a clue. In the Attack on Titan manga, giant humanoids are gobbling up humanity. It's a terrifying spectacle and you overlook the impossibility of the creature design. That is until a titan expert in the story points out how their anatomy isn't plausible and then also show how they don't have the same mass that normal creatures would for volume of flesh. They also evaporate away into mist upon death. They don't need to eat, have no digestive system, and vomit up whatever humans they do get. Tests show no known energy source to power them. They defy scientific investigation. There's also the matter of massive stone walls built to keep the titans out of the last human city and how that would be completely beyond the means of steampunk humans, especially when working in a rush. Oversight? No. It's a clue.

TL;DR I hate it when I have to remember it's just a show and I should really just relax. I love it when I get to turn on my brain to really dig into the material.


Re: The Great Oak Debate:

It's true: I was thinking of my local white and red oaks, and forgot the other varieties. (Which is pretty inexcusable, as Himalayan oaks turn up in the stories I have written that are set in that part of the world. Although those characters would, most likely, describe their local trees as "oaks." And have some special term for mine!)

It's ideolectical: when we talk about the thing we personally are most familiar with, we tend to drop the adjectives, and only use them to describe the ones that are more foreign--live oak would get an adjective from me, but white oak doesn't.

For example, a house cat is just a cat. All those other cats get modified.

(Specificity is a whole different lecture, however.)


Harry Turtledove does this a lot, probably deliberately. Alternate worlds somehow recapitulate World War II or the American Civil War or Byzantine history despite much earlier change points. I suspect that he does it for the money, since he has a PhD in history so must know how contingent historical events are.

I also think that there is a distinction between "soft fiction" where things happen because they are cool, and "hard fiction" where things happen according to well-defined rules about how the setting works. The later is a minority taste even amongst readers of SF and fantasy. A Robert E. Howard setting is a very different thing from a Larry Niven setting, even if both are telling fantasy stories about warriors and wizards set in the distant past.


I read Hornblower long before Patrick O'Brian and expected to feel as you do. But O'Brian was far superior as a world builder. The level of detail is much deeper, the characters are human. There is much more wit in the writing. Read the Aubrey books again particularly "The Return of the Medal".


Thoroughly enjoyed Lindsey Davis's Marcus Didius Falco stories set in the Roman Empire (c.70 AD).

What I look for and appreciate most in world-building is the mundane details. Otherwise, it's cheating. No two countries are alike, so I would expect that on a larger scale, worlds would also vary.

Arrakis (Dune) and Discworld are among the best SF world-building examples because these worlds are presented as 'naturally-occurring'. Their physical characteristics/natural histories matter to the story. Characters have to learn and deal with their planet's 'reality'.

In contrast, there's Well-world (Chalker) and Ringworld (Niven). These worlds are interesting mostly because the mystery of why they were constructed, the variety of 'life' experiments conducted and what such experiments say about 'people like us'.

On the whole though, world-building seems to reflect current self-understanding vis-a-vis the universe. In the 70's, tech solutions were very simple, and bigger was almost always the solution to a problem. In the 90s - when Discworld really took off - living with and within diversity which you didn't have to understand, but your life would be easier if you accepted, became a more popular world view.


All points well taken.

Since a big part of botany is "curing the green blurs" as one teacher put it (basically, learning how to identify plants), the specificity of the setting can be tied to the character. Someone from a distant city may see no more than a forest or a field, while a local may know the common names of the trees, and an herbalist or a botanist knows them not only by name, but by nature. In my neck of the woods, it can be brush (a clueless outsider), coastal sage scrub (an informed local), where I collect the black sage for my practice (the herbalist), or a patch of black sage and buckwheat that was saved from development about 20 years ago, but which now sits as an isolated island surrounded by subdivisions, and we're hoping that the gnatcatcher pair is still holding out in it (the expert).


Other things convincingly used as evidence of past climates: giant snakes. (just like really big scaly thermometers, apparently...)


Indeed and thats what really turned me into sf when I started reading Delany and Cordwainer Smith.

Who doesn't want to go to the ice cream parlor on a moon of Neptune - after reading "Time Considered as a Helix of Semi-Precious Stones"


On tree ecology, there's also the concept of the 'tree line', which is basically the point beyond which trees don't want to grow, due to cold. Go too far upwards, or too far North, and you stop getting trees.

For an illustration of this, check out Timberline Lodge, which is just where you'd guess from the name. Downhill from the building is a pretty decent evergreen forest; uphill, nothing. (No kidding, look at the picture.) It can be disconcerting if you're not used to the phenomena, as the trees just stop.


The causes of tree lines are one of those little nightmares that nature throws at ecologists.

So far as I remember, the best cause for treeline was that the winter air temperature gets to -50oF at some point in the winter. Trees have all sorts of ways of keeping their sap from freezing (ice crystals shred cells, so you don't want the sap to freeze). At around -50oF, cell contents will freeze regardless of what trick the tree uses, and the exposed tissue will die.

There can be krummholz above the -50oF line, but these are horizontally growing trees that are buried in the snow. Snow is a good thermal insulator, and it's pretty difficult to get something buried in snow to drop below -50oF even momentarily. This is why alpine and polar plants can grow as tundra (low to the ground) far north or upslope of the tree line.

Note that this is a -50oF momentary temperature, not an average temperature. This is the ecologist's nightmare: do you want to build the weather station that can withstand winter storms to record the critical temperature transition at -50? It's a lot harder than it sounds, since there's also snow, ice, wind, and lightning to deal with. Still, the -50oF mechanism is the best guess for how treelines function, based on physiological studies in the lab.

Note on the bigger picture: plants tend to be more sensitive to momentary or short-term stresses than to averages, just as we are. When you see maps of where species are supposed to move following climate change, these are based typically on average annual temperatures, with the average often taken in 10 or 20 year moving averages. How well does the average predict the critical extremes? Well, we don't know, since (so far as I know), we're missing critical exposure data for a lot of crops, let alone wild plants. This is what makes global weather weirding so unpredictable and perhaps catastrophic: a heat wave or cold snap can kill a lot of things that would otherwise be perfectly adapted to the average temperature of a place.


Everyday I see this example on Pikes Peak. Currently topped with snow.


Do the trees sometimes get a degree of herd protection?

Together they change the wind just enough they survive, but one tree a little farther gets less protection and dies when it gets big enough to get cold....

So you might get a relatively sharp boundary line instead of a wide gradual death-layer. Sometimes.


I've forgotten the name, but in some of the mountains of the northeast US and in Japan, there are forests with bands of trees like tiger stripes with meadow in between the stripes. Apparently it is caused by the very effect you pointed out: the trees at the edge get hammered by the wind and slowly die away, while the trees behind them survive, and new trees grow on the lee side of the band, where there isn't much shelter for a full-sized tree. Over the centuries, the bands are thought to slowly migrate up the slope.


Can we have that in sensible units, please? And, no, incidentally, that cannot possibly be correct. It does not, ever, get below -44C, anywhere in Britain, but we have a well-developed tree-line on mountains as "low" as 978 metres (Scafell Pike) or Ben Nevis (1344 metres) there used to be a weather station on top of Ben Nevis (it blew away in the end), but it never got that cold. [ FYI -27.2 C is the UK all-time minimum ]

It's a combination of factors. Cold + wind + growing season + soil + precipitation....

Wastwater, in Cumbria is only 61 metres above sea level & 79 metres deep (!) and as Photo 1 and Photo 2 both show have a well-demarcated tree-line. Remember, too, that this valley faces SW, into the warm, water-laden winds.


I'm less familiar with Scafell Pike and Wastwater than with Ben Nevis, but Ben Nevis is a stereotypical "steep rocky mountain". In short, there are lots of places where there isn't enough depth of soil for trees.


What a great thread.

The relationship between causality and narrative is fascinating, there are so many related topics. Understanding the perception of causality versus simple association (aka operant conditioning) seems surprisingly more complex than you'd think. And I suspect most of us "know" things due to some complicated sets of associations rather than reason or an understanding of causality than we'd like to admit to or even really believe.

Animals and small children apparently (as far as we know) lack the "causality" part altogether. This is not the same thing as lacking intelligence, and a clever series of behaviours derived from association can be (to us) indistinguishable from a perception of causality.

The ability to derive causality by constructing a narrative that links isolated samples of point-in-time knowledge of states is something that it seems we develop at the same time as a theory of mind and the ability to do what cognitive developmental psychologists call the false-belief task - the ability to understand that someone might legitimately have a model of the world that differs from yours.

I often wonder how complex my dog's inner life could be. And how different it could really be to a human mind, albeit an underperforming one without much more than what you can simulate by association, explain with operant conditioning. It still apparently contains cunning, craftiness, certainly affection and maybe even love.

On the other hand in lazy moments I think an impaired theory of mind is what explains conservatives...


Paws Rowan ( Mountain Ash / Sorbus acuparia ) will grow in rock-crevices with minmal soil, accumulaing wind-blown dust to make soil. Even they won't grow up the slopes of Great Gable ....


About tree lines, etc.

At about the 5,000 foot elevation level on Mount Washington (New Hampshire) there are full grown trees all of 2-3 feet tall. They are of the same family/type as the trees reaching a height of over 20 feet growing at a lower elevation of the same mountain at approx. 1,800 ft. This was confirmed when both sets of trees were transplanted to different elevations and then proceeded to grow to different heights. The 'Nature's Bonsai' version have extremely thin annular rings so that a diameter of under 2 inches equals a tree that's over 70 years old. So temperature in this instance resizes a plant right down to its cells. (As per the official SnowCat tour guide.)

FYI - Mount Washington is the highest elevation on the eastern North American coast with winter weather that rivals the South Pole, mostly due to very strong winds. The meteorology station at the summit recorded its coldest temp at -59F and highest wind speed of 231mph.


That's where bonsai come from. Originally, the tiny trees of the high mountains were dug up and transplanted into pots. The popular hori-hori gardening tool was reputedly originally used for transplanting bonsai out of the wild and into pots.

As for the British treelines mentioned above, I wouldn't blame lack of soil, because as you can see in the pictures with this article, some tree species have little problem with growing out of the cracks in rocks. Their soil is inside the rock, in the material in the cracks. The ectomycorrhizal fungi associated with some pine trees are capable of chemically etching rock to release nutrients. While I don't know if that's what is going on here, it's worth noting that trees and fractured bedrock often go together.

As for the British treelines, I don't know what the absolute cause is, but it may depend on the absolute lowest temperature that the local trees can survive. Despite what I said above, this depends on species. Orange trees, for example, start dying back at 32oF. Other species, of course, go lower. The absolute bottom for plants of any species is thought to be -50oF. This would be the range of bristlecone pines, larches, and the like. I have no idea what the freeze tolerance of British trees are, but if there's an area that gets colder than they can tolerate, they won't be able to grow above the snow there.


What's Scafell Pike made of? Ben Nevis is mostly granite, and that doesn't realy crack.


I'm in Florida. We had a winter back in I think '86 that had a really, really bad freeze. Every tree around lost leaves and the live twigs. We looked like fall up north. When the trees started sprouting again, you could see how even the tips of the old branches were dead and so water sprouts were coming out like crazy from all over.

So I get what's said about it not being the average but the extremes that determine what can survive but even dips below what is survivable can be survived if it's brief. A Florida freeze never lasts long. Give us two weeks of sub-zero temperatures, I think we'd be losing a lot more trees. Oddly enough, the palm trees came through fine for the most part. I don't recall seeing too many dead fronds.


Wikipedia, it say 'igneous rock'. However it's got a summit boulder field.

I suspect that a lot of the bare summits in the British Isles are due to the action of sheep. If a hill gets cleared, it's probably going to stay clear and over the centuries the chances of never having a fire burn off the top cover is probably quite low. Anywhere too steep for sheep is probably too steep for much of a tree. Given a few millennia without sheep and it might be that those tops would get covered by forests. But that landscape was pretty well scrubbed clean of any previous soil by the last glaciation, and humans, if not sheep, have occupied it since not long after the ice retreated.

(The oldest known human footprints from outside Africa were found in Norfolk — almost a million years old and dating from long before the last ice age and long before the domestication of sheep.)


Palms are fairly tough, or at least the ones grown in the UK are. They may be associated with hot desert climes, but remember that a dry desert frequently gets much colder at night.


Many years ago, I did my Bachelor's Thesis on constructing a tree-ring chronology of the trees near Peyto Glacier in the Canadian Rockies.

The trees growing in the valley of the glacier were often quite old. The oldest one I found had its earliest ring grown in 1234 A.D. Which set a record for 'oldest Engelmann Spruce known to be alive' (although this record didn't last long). This tree might have been 30cm in diameter-- its rings were tiny.

In the debris field where the glacier had been in the past, there were a bunch of trees that had been run over and ploughed into the ground. When we dug them up, we could produce matches on some of tree rings from the dead trees-- the oldest of the dead trees I found grew its earliest ring in 760 A.D.

The neat thing I found in my research was that the glaciers in the Rockies have been going forward, then backward, then forward, then backward, and so on, for a long time. So far as we can tell, each advance was progressively further forward than the one before it (so the 1844 maximum was slightly further forward than the 1713 maximum, which was in turn further forward than previous advances).

The glaciers in the Canadian Rockies were as far forward in the 1840s and 1850s as they have been in 11,000 years. Now, they're back (IIRC) to levels they haven't seen for 8000 years. And they are still retreating like crazy.


Treelines in Britain are not primarily caused by low temperatures. Wind is more important. There are also effects from high rainfall, waterlogging, soil erosion, and overgrazing. And in some places burning to develop grouse moors.

The treeline has been getting lower for 5000 years and is near sealevel in places. Its very low on Dartmoor, in southwestern England, where there are on average fewer than 20 days snow a year and no month of the year has a mean temperature below freezing.

In many places, especially in northern Scotland, forest regeneration is blocked by blanket bog, grazing pressure, burning, and windchill. If an area of mountain or moorland is fenced off to exclude deer, and possibly drained, trees often re-establish themselves well above e current treeline.

An aside which might seem a bit pompous and patronising - I can't be doing with degrees Fahrenheit and haven't really used them since the 1970s. In science everyone uses celsius/centigrade/kelvin and has since at least the 1940s. Even Americans. So as a first working assumption anything quoting temperatures in F doesn't come from a scientific source and is most probably misinformed. So I tend not to bother to translate them into real money.

Ken Brown (apologising for horrid Google ID)


Fascinating I went & burrowed in the stacks & came back with my ancient secondhand copy of Rachel Carson's "The Edge of the Sea" (1956) She said: This new distribution ( of temperature-sensitive littoral creatures) is, of course,reated to the widespread change of climate that seems to have set in at the beginning of the century & is noe well-recognised - a general warming-up noticed firdt in arctic regions, then in subarctic, & now in the temperate area of northern states. With warmer ocean waters north of Cape Cod, not only the adults, but the critically important young stages of soutern animals have been able to survive.

So, what's causing it? Some of it is "AGW", but all of it? Where is the energy coming from to raise the temperatures - is there something we've missed? Careful, btw, folks, bacause this sort of data will automatically be used by the "deniers" as "proof" that it is nothing to do with humanity's activities. Couple that with your remark that at the end - or just after the end of the "little ice age" - the glaciers were as far forward as they ever were, apart form the true Ice Age (even further forward than they were during the "Younger Dryas" ??? ) does raise interesting speculations.

We were talking about Causes & Effects, weren't we?


Don't forget that most crags in the UK have been heavily 'gardened' by rock climbers in the last 100 years and so don't naturally come all bare and rocky. In fact the BMC have to have tiding up days to keep the rock clear for climbers at the crags they manage. Back in the day turf was pulled off slabs by the square meter, climbers used to take trowels with them to get the vegetation out of the holds and famously a whole crag in the Lake District was once set on fire to get ride of the ivy. Generally modern climbers are much more savvy about ecology, but trees are still some times used as belays. Many have died over the decades. (Holly Tree Ledges have lost their holly trees.) I'm sure sheep have a lot to answer for nibbling fresh young shoots. In snowdonia, reduction in sheep numbers is increasing biodiversity on the hills. But climbers had a big effect on the steep bits, a bit like walkers and paths and we can't see it because we are so used to the way things look now.


Re: the great oak debate

This is a problem with trying to build in "a-ha" moments where it all comes together. A diverse audience of technical minded people is going to know more, collectively, than any one author can, so the author will be implying far more than he/she realizes, and probably not consistently.

I remember one description of an alien I read years ago. One of its characteristics was widely spaced eyes on the side of the head. It was supposed to be some scary warrior species, but to me that signals a herbivorous prey species (predators usually want depth perception on a single target while prey usually want wide-angle awareness).


Yep, hammerhead sharks the world over agree with you. So do chameleons, for that matter.

Still, it depends on the target audience. For example, Hollywood and movies in general are notorious for not giving a rat's ass about what experts notice in the background. This kind of kills it for any Korean watching MASH (which was filmed in Malibu, which looks very little like Korea), led to gales of cynical laughter from biologists watching Jurassic Park 1 and especially 2, long lists of everything that's not internally consistent in Star Trek, and so forth.

As an expert, I'd suggest that it's not worth writing solely for the experts, because a) there aren't that many, and b) most of them won't read it anyway. That said, fan service for the experts is a nice touch, because taking care of the small details elevates the story for everyone. That is, of course, if you can do that kind of detail work under deadline.

HOWEVER, if you're not a scientist and want to see how scientists actually speak and act, I'd strongly recommend seeing the movie Particle Fever. It's a documentary film about CERN and the discovery of the Higgs Boson that is really engaging for its portraits of some of the physicists involved.


You can see the effect of latitude on the treeline very clearly in the New Zealand subantarctic. In the South Island, trees grow well up the mountains, certainly over 1,000m.

In the Auckland Islands, a day by boat to the south, trees grow at sea level, but not on the hills. Vegetation has been modified by introduced mammals, but they haven't destroyed the woodland yet.

On Campbell Island, another day further south, the only tree was planted and looked after by Coast Watchers; you get native woody scrub at sea level, but herb fields above. Campbell Island is very windy, but rarely freezes, with summer temperatures of up to about 8C.

I think one of the issues is adequate summer temperatures to sustain growth.


You beat me to it with the chameleons! We think they are cute because they are small and weird. But imagine meeting a big one....

(I thought of mentioning them and then ended up spending a happy hour or two looking at websites with pretty pictures of chameleons and crocodiles and other various predators)

That would look alien. Yet they aren't of course. One of my major frustrations with some science fiction writers is the way their alien species are less unlike ourselves than creatures they could find if they went on an afternoons walk in the country. Or in their own homes if they had a decent hand lens. Written SF is usually better than TV and film skiffy, but it can be pretty bad.

Even far-future space-dwelling human cultures often come out as less unlike Iowans or Californians than most known human cultures are. Sometimes deliberately of course - the remade Battlestar Galactica series is obviously entirely populated by Americans (If not quite as obviously Mormons as in the first one). Sometimes due to a mixture of low budgets, scientific ignorance, and lack of imagination. The whole Star Trek franchise became unwatchable as alien after alien turned out to be a human with makeup on. Babylon 5 not much better.

If you are going to populate the universe with aliens who are in fact humans I. Disguise you better have a decent backstory for it. (Let us all praise Ursula Le Guin, one of the greatest SF writers - one of the greatest writers - of our times. And bloody good at world-building, including the back-stories that save the phenomena) Or at least allow room for the bright 14-year-olds to make up their own backstory (as CJ Cherryh just about does)

We humans share 99.96% of our ancestry with chimps. Maybe 80% with mice. Well over half with dogs and cats and horses. Perhaps a third with bananas. (Though they share far less of theirs with us, as their genomes are much, much, bigger and more complex than ours). Quite a large chunk of our genes are shared with every living thing on Earth, all the bacteria, loads of organisms most people have never heard of even if they do watch David Attenborough shows.

If an SF writer wants to have aliens that resemble humans more than they do bananas (or tardigrades, or dinoflagellates) they need a good piece of handwavium to ward off absurdity.

And they cant even hide behind parallel evolution. "Intelligence", broadly defined (some apparent self-awareness, tool use, flexible communications, adaptability to previously unknown circumstances, planning for future events, some ability to think about the mental state of others) evolved more than once on Earth. Us primates of course, but the other lineages that have it don't look like us. Crows and parrots have it (evolved separately or inherited from a common ancestor?). Some cephalopods do (Squids in space!). Elephants probably. Maybe even crocodiles (Be afraid! Be very afraid!). And likely other things too. And all that's just on one planet.

Ken Brown


Would enjoy an alien-encounter tale based on an avid (competitive) gardener looking for new interesting 'plants'. Gardeners have helped bridge cultures and increased trade but are usually ignored in contemporary stories. Doesn't really make sense that unless it's an indicator of how far away everyday life for most people has been removed from 'nature'.


The eye position thing is a rule of thumb, and has exceptions. For example, sharks seem to hunt more by smell, vibration, and electroreception than by sight. The bigger picture is that it's really hard to know what you're implying, or perhaps I should say it's hard to predict which particular combinations of facts the reader will put together to form an understanding of the fictional world.


My preferred space-faring body-type is the octopus. Cartilage is much more adaptable than bone plus it can form semi-rigid limbs/angles. Also the octopus has suckers for grasping, etc. which could be further developed to exceed the 'opposable thumb' advantage humans tout.

Arrived at this while thinking how a human body would have to be 'adjusted' for long no/ultra low gravity flight after having read Chris Hadfield's book. Haven't checked whether trading to cartilage would help resolve the immune system problem: apparently weightlessness while contributing to osteoporosis also does a number on/weakens the immune system. (No idea what exactly - apart from location - the b-cell immune system and osteoporosis have in common as I'm not a scientist/techie.)

This then led me to another thought ... if we would need to adapt our bodies for space flight, so might species from other planets/galaxies ... which means that any visitors we met in the flesh would probably not be representative of their actual species.


Cephalopod immune systems are very different to the human - or even mammalian - one; they've no adaptive immune system. Vacuum's effects remain unquantified, as far as I know (which is, to be fair, not far at all). More importantly, the octopus already has the one thing any microgravity-dwelling organism would give a manipulatory appendage for: built-in jet propulsion!


Is the 'no adaptive immune system' true of all creatures without bone, or just cephalopods?


Well, conventional wisdom is the mammal-like adaptive immune systeme evolved from some aspects of the innate immune system (lysozym and like) about 500 million years ago in jawed vertebrates; that would exclude lampreys and like, though it seems even those have an immune system somewhat similar to ours, though derived by parallel evolution.

As for cephalopods, the articles on mollusks I found deal mainly with innate responses, but then, as with the lamprey nobody cared to look. Also note that with biological research, the whole of Lophotrochozoa (cephalopods, snails, earthworms and assorted slimy ciliate-tentacle mouthed crawlers) is somewhat undersampled compared to Deuterostomia (sea urchins, humans and related pervert critters into the whole n cups, m girls shtick) and Ecdysozoa (Drosophila, C. elegans and a host of other animals not fit for consumption according to Leviticus and overly concerned with wardrobe ). I remember a paper that tried to settle the good old metazoa evolution question not including any...

As for immune system and space travel, tumor killing NK cells, the part most important for space travel, are part of the vertebrate innate immune response, though I don't know if they are extant in mollusks. Does the Kraken get cancer?


Funny thing is, I actually found myself recently making the argument that Star Trek wasn't quite as stupid as it seems, in that one can make an argument that starfaring intelligent races will look roughly human.

Here it is, and feel free to take potshots:

First, it rests on the critical untested hypothesis that humans can travel between stars. Both Charlie and I think this is actually unlikely, due to the fact that humans need Earth-like conditions and a biosphere to live within (see the Chris Hadfield book mentioned above for a really good description of what life in space is really like). That said, I'm assuming in this argument that humans can travel between the stars somehow.

Thing is, starfaring technology ultimately depends on one of the oldest human technologies: fire. Making fire is something only humans can do, and almost everything that would go into a starship has to be processed through externally applied heat somehow. Fire is the essential "killer app" that separates us from all the other tool-using and language-using animals. Yes, I know that Kanzi the Bonobo learned how to make a campfire and light it with a lighter, but what I'm talking about is the ability to make a fire through friction.

If you've ever tried to make a fire with a hand-drill, you'll know it's not easy. You have to get two pieces of the right sort of wood, straighten one piece for a drill and put a point on it, then carve a notched socket into the other (the socket), and perhaps flatten it for easier holding. Then you have to make some tinder. All of this requires precise grips and tool making. Then you have to spin the drill as fast as possible while bearing down with enough pressure to maximize the friction, which requires some fancy coordination from your shoulders, arms, and hands, plus a foot holding the socket still while you drill into it. I've never succeeded at this step, although I've developed some impressive blisters trying. Once you get it hot enough to generate a very small coal, you have to transfer the coal to the tinder before it goes out, then very gently blow on it until the tinder catches fire. This requires precision grips and also precision blowing from the mouth.

Now, we know a human-shaped being can do this. But this essential and homely technology requires quite a lot. You need a body form that can apply both a precise grip and a power grip in rapid order, along with precision blowing to get the coal to catch, along with a sophisticated knowledge of the friction and tinder properties of local materials.

How many other animals on Earth can even structurally do this? An octopus couldn't do it, nor could an elephant (how would they spin the drill with a tentacle?). Racoons are probably too small to generate enough force, as are most monkeys. Perhaps Kanzi the Bonobo could learn, but I'm not sure he has sufficiently precise control over his grips and breath. Alex the Parrot, who was certainly intelligent enough, couldn't generate the force needed nor spin the drill.

Yes, everyone immediately jumps to the alternative of using two stones to generate a spark. That's nice--find those stones. It's a lot harder than finding two pieces of suitable wood. Striking the stones together and catching the spark in tinder isn't much easier either. There are a bunch of other ways to start a fire without a lighter, but they all involve similar combinations of force, precision, and blowing the fire alive.

So I'd say that, if we make the untested assumption that humans can make starships, and make the stronger assumption that only fire-making species can make the necessary precursor technologies needed for a starship, then it's quite likely that any other alien starship makers will look roughly like humans, simply because, by sheer accident, our shape turns out to be capable of making a fire.

Note here that I'm not talking about intelligent alien species. There's no reason to think that an alien could look utterly unlike a human and be at least as intelligent as a human. In fact, there's no reason to think that a intelligent alien species couldn't make some sort of complex society without fire. However, I'm going to assert that, if they can't make a fire, they're not going to make it into space. While I think intelligence is necessary to go into space, I don't think that intelligent species automatically go into space.

Now, of course, the way to disprove this hypothesis is to design a non-humanoid alien that could make a fire by friction. I'm sure it can be done, and it makes a nice test for anyone who wants to design an alien starfaring species. Until such designs start popping up, I'd suggest that the humanoid aliens of TV and the movies may not be quite as silly as they seem.


Larry Niven's "Outsiders" ??


Take a look at the second method listed here. What precludes elephants from doing their firestarting in teams?


To spin a firedrill, you need to spin it back and forth rapidly and with the drill in line with high pressure exerted down the line, perpendicular to the plane of rotation. I'm not sure tentacles can accomplish this task, whether they're managed by one being (an octopoid) or several (elephants in a team). Humans do it by holding the drill flat between two flat palms and spin it via friction. That's why it's so easy to get blisters on your palms with this technique.

The problem, as I see it, is that the tentacles will be wrapping and unwrapping on different parts of the firedrill, and this will tend to cause the drill to tilt and fly out of the socket. Perhaps there's a way to do it with three tentacles, with the third tentacle holding a socket on top to keep the drill aligned with the bottom socket? That's awkward, to say the least. I have used a bow-drill successfully (which uses the top socket), and it's real easy to dislodge the drill with a bow-drill if you're not careful. With an elephant's trunk, I'm not even sure it can be wrapped and unwrapped far enough and fast enough to generate the needed friction, although I could be wrong.

If you can figure out how to do it with tentacles, so much the better.


If the oxygen content of their atmosphere was noticeably higher, making fire would be much easier. Also, any lenslike or mirrorlike structures they could find in nature (e.g. whale or elephant eye lenses) would make firestarting simpler.


Might work. Of course, the last time we had very high oxygen levels was in the carboniferous, when we had lots of trees, but fungi and termites hadn't yet evolved to break down the wood and release the CO2 back into the atmosphere. It was also favored by Earth being in an icehouse configuration (as it is now and it was in the Carboniferous), where there was lots of erosion from rapidly-rising mountains, and the erosion was stripping CO2 out of the air. Of the two, undecomposed forests are probably better at stripping CO2 and raising O2 than erosion alone.

So if we have a world where the local intelligent beings are able to dissect lenses out of eyes (presumably by creating microlithic flint or obsidian blades), then that world would be dominated by a lot of undecomposed carbon (read trees and swamps), but it would also have lots of mountains and probably large polar ice caps.

And...the intelligent aliens would have to be dissecting eyeballs simply for fun and profit, before one of them was goofing around with a dissected-out lens (gooey!) and noticed that a lens could be used to focus sunlight down. And the sunlight would have to be sufficiently regular (notice the weather conditions listed above--it might get cloudy) that this method works often enough to be useful.

As I said, it might work, but that places some strong constraints on the world. Would this method even work under a M-class star, for instance?


the intelligent aliens would have to be dissecting eyeballs simply for fun and profit

I assume that method of firestarting would most likely be discovered by predators or omnivores. They'd need enough manipulation ability to dissect the lens from the carcass, but that's it. After that, it's just like starting fires with a magnifying glass, which works on Earth.


Except there's no spinning whatsoever in the method I pointed out; it's a three-person firesaw.


Heck, try it out with three people all working one-handed and see if you can make it work. I've never tried a firesaw, so it will be interesting to find out whether it can work or not.

As for magnifying glass fires, they work on very sunny days, but not on cloudy days. Someone with a better physics background can probably tell you how many watts/mm2 of energy at whatever wavelength is needed to ignite tinder, and then we can back-calculate and figure out what kinds of stars allow this method to work. I know from experience that a handlens on a cloudy day doesn't work, and I suspect that a red dwarf would be problematic too. In the latter case, any habitable (by our standards) planet has to be tidally locked to its red sun, and the most favorable zones are closer to the line between permanent day and permanent night. Because of this, the habitable zones don't get that much light, and the light they get is proportionally weaker.

The point here is that, if you want to go with an eyeball as a fire starter on an oxygen rich world, you've radically limited the environment of your world. Basically, it has to be a swamp world with glaciers and lots of mountains, but paradoxically, where your firemakers live, they have to have a lot of very sunny days. Fire by friction is possible under a much wider set of circumstances, but it is more constrained by the anatomy of the firemaker.


Remember that it's a curious and unexplained feature of Earth's flora that the main absorption bands for photosynthesis are red (680-700 nm) not blue or violet. If the local tinder is more reasonably colored, it will be easier to ignite with a lens.

I don't know about every circumstance, but using elephant eye lenses probably would work in the African plains, where humans have occasionally hunted elephants for a very long time.


Sorry to ask, but why insist on lenses?

While we might argue if Archimedes' death ray was feasable

we could use substances with a somewhat lower ignition temperature

and a somewhat better weather.

As for the rationale, let's just say the species evolved a reflecting surface for various reasons, including courtship and distracting enemies or prey.

All it takes is just some bored young members of said species trying to aim at one area, something somewhat reminding me of games young males of a certain primate species sometimes do when urinating...


In fact, there's no reason to think that a intelligent alien species couldn't make some sort of complex society without fire.

Once you have an intelligent alien with a complex society, they'd be able to take a naturally-occurring fire and use it. The Prometheus technique.

You need the society to be complex enough to keep the fire burning, or at least smouldering, but that's not such a high bar.


Yes and no. One thing we don't understand at all is how human ancestors learned to make fire. I'd take it as given that hominids were playing with wildfire coals (and possibly volcanic lava, given that our ancestors evolved in the African Rift Zone) long before they figured out how to make fire through friction.

If you think about it, there's something weird about a species that couldn't figure out how to make a fire, but could figure out all the uses of fire to make advanced technology. For example, compared with making a fire, smelting and working metal is hard, and that uses basically all of the same natural adaptations that firemaking depends on.

This is why making fire through friction is a nice little hurdle for an alien to clear. If a species has the body structure that allows it to make fire through friction, a lot of technologies are possible. If a species can't make fire that way, what else can't it do? This is one of those questions about implications.


"Thing is, starfaring technology ultimately depends on one of the oldest human technologies: fire."

Your concepts are utterly anthropocentric. Which is fine, they're interesting to think about.

But -- consider the habitat in Larry Niven's Integer Trees. Is there a way to get habitable areas in zero gravity? At first thought, it seems like there would be nothing to keep an atmosphere together except gravity. That's because of my lack of imagination. I don't really know much about what's out there, except for suns. Those are what particularly intrude themselves on our attention. We particularly think about planets because we were born on a planet.

Suns. An intelligent species that lives near the surface of a sun, or deeper, would have its own special difficulties with space travel. I know nothing about what that would be like.

Getting off a planet. We think in terms of fire because that's how we think. Others might think in terms of a mass driver etc.

Making fire. We think in terms of the ways that used to work best for us to make fire. But we used to keep coals in a bed of ash inside a wicker etc container, it was usually easier to store fire than to make fire. And borrow fire rather than make it. We think in terms of tinder because dry tinder is often easy to get in our forests etc, except when it's wet. If we wanted fires when fires were harder to start, we would carry around particularly good tinder, perhaps waxy stuff with some volatile oils in them. Something that will burn from the smallest spark, that usually must be kept sealed to keep that tiny spark from reaching it....

We tend to think of starting fires in minutes or hours, but if yuou don't mind waiting days, fermentation could do it. We tend to get silage fires in weeks by accident, but if we tried to make it happen we could get it a lot faster.

Horses for courses. We think in terms of bow drills because that's something that can work for us. If elephants wanted to make fires, they might wind up using something that emphasizes their strengths. They are much better than us at blowing on things, so they might find ways that involve a whole lot of blowing moist air. I don't right off know how that would work because I am not an elephant. Possibly elephants might produce methane fires, since they can easily get methane which at 5-15% concentration in air is kind of explosive. I thought it was supposed to explode from sunlight but a quick search didn't show that.

We try to do things the ways that are best for us. Then we say it would be hard for aliens who weren't shaped like us to get our results because they aren't adapted to doing what we do. But we do those things because they're what our shape adapts us for.


I'm not sure it's unexplained--I'd have to ask the plant physiologists. I may have even heard the answer, but photosynthesis is a fairly complex operation, and it's not one of the details I remember offhand.

The basic thing to remember is that modern photosynthesis evolved under an anaerobic atmosphere something like 2,500,000,000 years ago, and both the atmosphere and the sun were very different back then. The sun was a lot dimmer, and the atmosphere had no oxygen and a lot of carbon dioxide. Photosynthesis was optimized to those conditions, then progressively tweaked by evolution as the atmosphere changed and the sun slowly brightened.

Photosynthesis' evolutionary pathway still causes problems, because a primary photosynthesis enzyme, rubisco, is poisoned by the presence of too much oxygen. Rubisco evolved in an environment without free oxygen, and it's stayed that way ever since. Rather than trying to re-optimize the enzyme for the modern atmosphere, plants have evolved a bunch of mechanisms to cope with its shortcomings, from enriching the around the chloroplasts to absorbing extra light so it won't cause damage by making too much oxygen.


"You can just make anything up, can't you..."

Pratchett's response (in the mouth of Vetinari, a world-builder within a well-built world) is apposite: "You think that just because I can do anything, I can do anything".

Unfortunately interlocutors smart enough to be stopped by that response are generally smart or knowledgeable enough not to make the accusation in the first place.


Re oaks: I agree with Bear. An oaken chair (in a castle or a town) implies oaks near either navigable rivers or fairly dense settlement; probably both. Hence lowland, hence temperate climate. Tropical montane oaks won't cut it, except in a story by Borges.


VERY EASILY possible, as was demonstrated by fuckwit "architects" in London last year Cars deformed, plastic melted, eggs fried on windowsills, temps of over 90C recorded - & this was in Autumn ..... Google "Walkie scorchie" for more info.


Actually context can change many things. "Oak" in Australia usually means "Tasmanian Oak" which can be the same thing as "Victorian Ash", one of a handful of hardwood eucalypts. Sure it in turn has its own implications about growing conditions, but the point is that names can be a bit more fluid than we usually think.

It partly makes my point above, I think. We learn names by association; where we learn the name for the thing by way of understanding what the thing is, we strongly tend to act as though the name came first (as it might have done for us). In SF naming novel or alien things by analogy with existing or terrestrial things tends to make the reader interpret them according to existing associations. If there's a rational/logical pattern in world-building that the reader might unravel, that's a bigger plus, but if one goes a long way beyond "mere" association it will be beyond most readers too (much as most people/readers would be loathe to admit it).

Tassie oak is a lot less durable than English oak, but it has a marvelous patina under french polish :)


Sure, reflecting surfaces could work. I mainly considered lenses because they're an integral component of eyes, which have evolved independently in over a dozen lineages on Earth.


I'd suggest anthropomorphism. Avoiding anthropocentrism can become a blinding reflex if you're not careful, as the reaction to the Clever Hans phenomenon showed. Bias against Clever Hans blinded generations of animal researchers to the possibility that non-human species could be intelligent (and if you look at BF Skinner, it arguably even blinded some researchers to the possibility that humans could be intelligent).

Taking your comments in reverse order, there are probably a dozen ways of making fire by friction. The problem with all of them is that they all require knowledge, reciprocating motion, a fair amount of strength, highly precise motion, and precise breath control. The strength and precision are because the method basically uses muscular strength to ignite a piece of wood, and the only way to do this is to focus the work of muscles in a small area of suitably ignitable material (and most plants aren't very ignitable, whatever the fire industrial complex wants you to believe). This focused effort isn't easy, and it needs to happen for several minutes at least to get an ignition. Then, once a coal is produced, it needs to be transferred to a tinder bed and blown alight, which demands another set of precise motions. Taken together, this is a demanding set of tasks for any animal. On Earth, only humans undeniably have all the abilities, although many other animals have some of them.

There are certainly other ways to make fire, but fermenting silage isn't dependable in space or time. As for carrying coals around, I'm quite sure that our hominid ancestors did that for a very long time before they figured out how to make fire through themselves. After all, we evolved in the African Rift, which has both wildfires and volcanoes. The thing to remember is that making fire is simple compared to, say, smelting metal or working ceramics. If a species lacks the physical structure to make a fire, why expect it to smelt metal with the fires it has? They require the same adaptations. It's worth breaking down all the technologies we have, and see which of them can be performed without that bundle of abilities needed to make a fire. Some can (like farming, which ants do), but many can't. Making fire by friction seems to be a good, simple test for designing an alien. Firemaking is not sufficient to make a technological civilization, but I'd argue that it's necessary. If your alien can't make a fire, asking it to make a starship is much more improbable.

As for getting off a planet, the method doesn't matter. Imagine a mass driver or even a jump gate that doesn't involve fire in some part of its manufacturing. This isn't at all about rockets, it's about fire and technology.

Life on the surface of a star or in other exotic environments? We know how to look for that. As James Lovelock pointed out back in the 1970s, life creates a biosphere that is far from chemical equilibrium. This can be detected through analysis of alien atmospheres through spectroscopy. If a star had a biosphere, its bizarre chemistry would give it away. While stellar life wouldn't need to make a fire, it would need to be able to do chemistry (of which firemaking, smelting, ceramics, etc. are all subsets) if it wanted to make the devices it needed to get off the surface of its home. Just at a guess, most species in a stellar biosphere would have trouble doing that. With the Integral Trees, the same issues apply, if such an environment can even exist in reality.


Magnesium and sulfur bits can be used to start fires and this technique does not require much hand-strength or coordination. There are probably other chemical fire-starters around. I think the point is being able to make fire on demand. There's also the 'rain drop lens' - saw a TV show that demonstrated this technique. Weather is a factor whether relying on dry twigs or sunlight. Keeping the cinders alive would be the next step.

Going back to my 'octopus' comment: I didn't mean that the aliens would be octopus-like but that this might be a body plan to consider as a tweak to human spacefarers to make space flight/life tolerable/survivable.


Magnesium and sulfur bits can be used to start fires

Any species that has access to elemental magnesium has probably solved the fire problem millennia ago.


Well, there are some other ways to get to magnesium, e.g. electrolysis. And magnesium is quite light, making for good armor, so given the copper some annelids use to strengthen their teeth...

BTW, AFAIK magnesium or aluminium are also used in some LARP armours; yes, we already made jokes about what happens when lighting it up. Though judging from the fun burning computer cases, it might be a nontrivial task:


There is the problem of contingency. We got to elemental magnesium via fire. And we got to a lot of other things via fire. But that's because we had fire, and so we used it to get places.

How, or if, we could have got to those places without fire is difficult to tell, because of the ubiquity of it. Pretty well every human culture is based on knowing how to make it, with possible exceptions being the Tasmanian aboriginals and the Andamanese aboriginals. But even in the latter case they used fire, they just expended a lot of care on keeping flames going once discovered.

(I have seen a fire that is said to have been kept lit for 1200 years, but whether that is truly the case or whether it ever got relit in the middle of the night I could not say.)


And also by making so much rubisco that its probably the most abundant enzyme on the planet.

The form of photosynthesis used by green plants and cyanobacteria (there are others) is wonderfully complicated. Two photosystems, each with a different light-harvesting complex, a bundle of metabolic pathways apparently recruited from heterotrophic catabolism and respiration and sometimes turned backwards and joined at the ends into cycles, and three or four carbon fixation mechanisms (each species usually only uses one, or one at a time) And massive electron transport chains that I never managed to get into my head except possibly the day before an exam. And wonderful ATP synthetases that are powered by protons falling through pores in membrane proteins, driven by electric fields made by pumping electrons the other way.

But this all seems to have evolved once. One evolutionary event. And quite likely taken up by eukaryotes only ones as well, as symbiotic cynaobacteria were made into chloroplasts. Another single evolutionary event (even if it did take hundreds of millions of years). So as you say, the wavelengths of light used were not adapted to the varied lives of existing species, they are contingent, historical, inherited from one common ancestor. So now locked in, apparently unchangeably. It seems to have been difficult to develop in the first place, now its good enough, so nothing has come to compete with it. There are hundreds of other biological systems that are in the same situation. They do not need to be perfect, or even better than anyone elses's. Just good enough. That's how evolution usually works.


It's not that elemental magnesium implies "fire" so much as that elemental magnesium implies "lots of energy". On Earth it was incredibly rare until the mid 20th century, like aluminum, because it cost so much energy to make. Of course, once you have lots of energy at your disposal, setting combustibles alight ceases to be much of a problem (in appropriate environments, anyway).


Thank you for saying it so well. Hopefully that answers Jay's original question.


"I'd suggest anthropomorphism. Avoiding anthropocentrism can become a blinding reflex if you're not careful...."

We naturally extrapolate from our own experience. What else do we have? It's what we know. But we're guessing what we don't know from our limited experience, and it's misleading.

"Taking your comments in reverse order, there are probably a dozen ways of making fire by friction."

Yes, probably thousands of ways.

"The problem with all of them is that they all require knowledge, reciprocating motion, a fair amount of strength, highly precise motion, and precise breath control."

They need reciprocating motion because we aren't good at rotary motion. Etc.

"The strength and precision are because the method basically uses muscular strength to ignite a piece of wood"

And because we have wood available. Many places they will have something else.

"There are certainly other ways to make fire, but fermenting silage isn't dependable in space or time."

Pretty much all our experience is trying to dependably keep it from setting fire, and we aren't all that successful. We could probably get it to light very dependably if we tried. But why should we? We have matches.

"The thing to remember is that making fire is simple compared to, say, smelting metal or working ceramics."

Sure. And making a net is simple compared to tailoring clothes or laying out city streets and circuit boards. You picked one that was central to us, but something else might be central to a different technological path.


Hmmm. "Maybe it's something we haven't thought of" is a perfectly valid question. Still, a far better question, especially in this thread, is "what if?"

Looking back, I've been entirely too verbose here. I'd suggest that you describe a hypothetical alien that is physically incapable of making fire, yet, by making some else "central to a different technological path," it can get to the stars without making fire. I honestly don't understand what this something else might be, since humans use a wide variety of different technologies, but whatever. Probably that's my ignorance speaking.

After all, I think everyone, especially including myself, would be happier if that assertion about human-shaped aliens could be disproved, even with a single good counterexample. I'd say go for it. Describe your alien. I'll be happy to cheer you on and admit I was wrong afterwards.


Thanks for the thought; The actual type of rock rather than just igneous, sedimentary or metamorphic is important here though. Basalt fissures much more easily than granite, never mind Lewisian Gneiss.

Having said that, I'd agree with you about the effects of sheep in the Lake District (and some but not all parts of the Scottish Highlands).


After some searching I found something a little more precise.

Apparently, it's the Borrowdale Volcanic Group rock formations, being mostly Andesites but also Basalts and Rhyolites. So not nice solid Granite.


Thanks again; that proves the point that there's something for trees to stick in down there, and also places a restriction on the size of an individual tree (cramping of the root system).


Almost all of Britain was wooded after the last ice retreated. Maybe not the sort of total treecover they used to imagine a century ago, as if a squirrel could go from Dover to Cape Wrath without setting foot on the ground - its now thought likely that a lot of it was scrubbier than that ad also perhaps kept open by large herbivores - but there were trees and there was soil almost everywhere. Even on the high tops. Open moorland is much more recent, and probably down to human activity.

For what its worth there are many types of rock on Scafell Pike. It, and the other fells around it, are the eroded remains of a volcano, and different eruptions spewed out different complex mixtures of minerals.


To illustrate the point I was trying to make with what I hope is a better example, FTL travel implies causality breaking, matter with negative energy, power sources that make nuclear reactors look like hearing aid batteries, and a host of other things. The majority of science fiction books aren't going to deal with any of that.

As a reader, it's hard to guess which sorts of extrapolations from the written facts are going to deepen my understanding of the fiction, and which are only going to poke holes in it.


"I'd suggest that you describe a hypothetical alien that is physically incapable of making fire, yet, by making some else "central to a different technological path"[...]"

The problem is that since I'll have to make up this alien out of my imagination it might not seem plausible to you. If it was a real alien I could point at it and say it doesn't matter whether you think it ought to work that way, here it is. But I can't do that.

So I imagine a low-gravity water world with an atmosphere that has no free oxygen. A lot of sulfur.

We got first sulfur photosynthesis and later oxygen photosynthesis. I don't know which is energetically more efficient, I suspect the oxygen is, but maybe more important oxygen is far more plentiful than sulfur. So sulfur photosynthesis only survives here in little anaerobic pockets that have sufficient sulfur. I saw the purple once in a puddle of water above a big coal field. On this world it's the sulfur photosynthesis which dominates, and there is no land life since there is no land. (I have no idea whether it's plausible that there could be a world with no dry land, maybe the geology requires that dry land has to happen. I dunno.)

In our oceans most of the plants are tiny. They get eaten fast so they must grow fast, and they divide and separate quickly so both daughter cells won't be eaten in one bite. But in my hypothetical world ocean the plants have the advantage. They grow until they form a surface mat just under the ocean surface, and they develop structures to collect nutrients from deeper water. They also develop structures to deliver waste products into the air and deeper water, wherever they can get a good gradient.The plants make tough structures that are hard to separate and hard to digest, and also they make lots of effective poisons. Over time they build increasingly elaborate structures.

Meanwhile some animals develop special guts that can provide a safe place for bacteria to digest plant debris on the ocean bottom, and some animals manage to live off the plants' waste products. A small minority of animals predate on others. They develop eyes and luminescent flashes as on earth. (Would they do that with plants shading out most of the sunlight from the top 20 meters of the water? I say so.) The animals that would later become intelligent have multiple stomachs each with an opening to the outside so that they can move food from stomach to stomach as desired, and also smear a variety of digestive juices on anything. So, we make hydrocholoric acid and a few caustic enzymes that we have little access to. These could also make sulfuric acid, phosphoric, etc plus a bigger variety of enzymes -- all easily usable.

Various animals learn to live as commensals among the plant communities. The plants select them to fit in. Animals that are not adept enough at avoiding poisoning, die. When an animal hurts the plants a whole area turns poisonous, so the animals learn to police each other and to flee conflict. Animals trusted by plants as pollinators and for seed dispersal learn to breed plants to better serve them, and the intelligence evolves both to deal with predators, and with dominant plants, and with each other.

Their science would at first be dominated by biology and then chemistry. They would learn to precipitate metals but would have little practical use for them -- not the strongest, most durable, sharpest, acid-resistant, or cheapest. Study of oxidative phosphorylation would lead to redox reactions across membranes and then over distances, COmparison to biological motors would lead to the equivalent of electric motors -- redox reactions to create rotary motion.

Given a bag of seawater and a wetsuit they could leave the water for short times and explore the atmosphere. The view from topside would eventually give better concepts of rain, wind, clouds, possibly thunderstorms, the sun, probably a moon or two, and eventually stars. They might learn to make kites and eventually manned kites. (A kite is useful for towing stuff if the wind and currents combine well for you.) Then gliders, Gliders might use hurricanes to reach high altitudes. (Terran hurricanes can reach 50,000 feet.) They might find ways to use great big balloons to reach higher. (Our maximum, 100,000 feet?) Would anyone seriously want to build a palace in the sky? You'd have first crack at the sunshine. But we're talking about lifting quantities of seawater, not air.

Would they get the concept of making things fly fast through air? They could. Particularly if they do warfare. Fly right over the enemy's center and empty a big stomach at them....

If everything is good at sporulating then they could reach space with light-weight ecosystems that could travel slowly. A whole freeze-dried ecology, just add water, enough sulfur, etc. Without that they need a way to move heavy stuff, and everything I think of translates to rocket fuel. They could do that. They could visit the barren planets of their system, if they wanted to badly enough.

As for how they could reach the stars, I don't yet see any way for humans to do that either. Something might show up sometime in the next few hundred years. Three hundred years ago the best idea anybody had for getting off this planet was with a great big gunpowder cannon. They'd never heard of thermite. Maybe someday we'll come up with something workable for interstellar travel.


Works for me, except for that first step from sulfur to oxygen. Unfortunately, my sheet of electron receptors and electron donors is buried deep in my archives, but I do remember that oxygen produces the most energy as an electron receptor, and there's no evidence on Earth for a complex multicellular organism that uses sulfur in place of oxygen. To the people who study the subject, this strongly suggests that multicellularity requires oxygen. Still, if this gets disproved (which would be tricky, but probably doable in a decade or so), your story could work.

Thanks for taking the time to sketch a scenario out.


In our oceans most of the plants are tiny

The free floating ones, true, but kelp forests grow pretty damned big. Are these mats free floating or are they rooted on reefs? I'm sort of assuming the former, a kelp-like Sargasso.

(Whether you'd get the surface vortices that makes a Sargasso or a Pacific Gyre with no actual land to deflect currents is something I can only guess at.)

But I quibble - you seem to have done some impressive working out there.


Forget anthropocentricity: why are you assuming lignified cellulosic synctiaia (xylem vessels) are going to be found in an alien biosphere where hominid-like aliens are, well alien? Are there no other solutions to transpiration and raising an eluent fluid (in our biosphere'a case, water) by capillary action/Van der Waals force?

Rejecting anthropocentricity is not enough; you also need to reject the plant/animal dichotomy if you want to reason about alien spacefarers.


Note that I am (a) drunk and (b) typing on an iPad mini in a Polish real ale bar while (c) playing catch-up on my blog entries. Ergo, (d) tyops here.


Firemaking is not sufficient to make a technological civilization, but I'd argue that it's necessary. If your alien can't make a fire, asking it to make a starship is much more improbable.

This is a REALLY IMPORTANT INSIGHT which I intend to brandish in public at every appropriate opportunity. Thank you.


Crazy random question: is it possible that the wavelength of light that chlorophyll is optimally tuned to absorb is actually related to the solar radiation output peak about 1-3Gya ago (or whenever modern chlorophyll first evolved) rather than today's? At a time when the sun wS somewhat dimmer and emitted radiation at longer wavelengths? Given that the sun is slowly brightening, what are the implications for the biosphere over the next 0.5-2Gya (i.e. gradually declining efficiency of photosynthesis)?


Would anyone seriously want to build a palace in the sky? You'd have first crack at the sunshine. But we're talking about lifting quantities of seawater, not air.

Mind uploading into robot bodies designed for survival in the anaquatic, rarefied gaseous environment of the troposphere. HTH.


Simples: just make it a Generation IV star system. Ours is Generation III—our metallicity is the product of two generations of supernovae. Add another generation of supernova-induced metalosynthesis and the periodic table will look skewed towards heavier atomic numbers. Also, enzyme chemistry will be REALLY WEIRD. All that arsenic, y'see ...


Interesting point: older generations of planets/star systems with different chemistries.

Thinking back to a Nova/PBS show ...

Sulfur-loving organisms growing near undersea volcano vents could evolve if the volcanic activity wasn't too extreme and killed them all off. We'd need just enough stress to let the process of evolutionary selection work. In such an environment, sapient creatures might wonder where the lava that spewed out during especially strong eruptions went to. If that lava contained any important (wealth-making) bits, then the local civilization would probably conduct research. This would necessitate learning how to break the "water barrier", travel in air, etc. But the point is that they would probably model their rocket ship on the volcano -- heat, pressure, thrust, etc. (Not all that different from our rockets.)

Learn any drinking songs whilst enjoying your Polish beer?


"I do remember that oxygen produces the most energy as an electron receptor,"

I don't remember that, but it just plain makes sense it would be true. Still, that isn't the only criteria for success, and possibly having so little sulfur available was what tipped the balance.

"... and there's no evidence on Earth for a complex multicellular organism that uses sulfur in place of oxygen. To the people who study the subject, this strongly suggests that multicellularity requires oxygen."

That's judging from one example. Most multicellular organisms are eucaryotes, and maybe eucaryotes incorporatec chloroplasts only once. They might never have had the chance to try out sulfur photosynthesis. Or it might have been tried, and was uncompetitive at something eucaryotes needed before any of them became multicellular.

I suggest inadequate amounts of sulfur as one possibility. The salmonella sulfate transport protein has no cysteine and only the n-terminal methionine. Assuming this was selected, perhaps there have been times when sulfate was growth-limiting. So sulfur photosynthesis might be more competitive in an anoxic ocean with more sulfur than it was in ours.

Still, we are imagining things we don't actually have data about, and you have every right to feel that any of it is implausible.

"The free floating ones, true, but kelp forests grow pretty damned big. Are these mats free floating or are they rooted on reefs? I'm sort of assuming the former, a kelp-like Sargasso."

That's what I assumed, reasonably deep water everywhere. For all I know any planet with water oceans has to have vocanoes sticking way up and maybe subduction. I want to assume that it's possible to have everything free.

"(Whether you'd get the surface vortices that makes a Sargasso or a Pacific Gyre with no actual land to deflect currents is something I can only guess at.)"

Same here. I imagine you could get climate bands like the rings of Jupiter. Plants might evolve ways to keep coriolis forces from gradually pushing them out of their livable range, not least to hold onto each other all the way around the world. I could imagine bands where you get permanent hurricanes, or transient ones, that tear up the structures and leave a lot of floating wreckage behind.

Likely they would think in terms of cultural relationships more than national boundary-lines. Their concept of geography would likely be rather fluid.


Note that water depth maxes out when hydrostatic pressure exceeds on the order of 1GPa -- you then get interesting phase chemistry; ice can exist in phases with density > 1.00 so that it sinks in water. Upshot: you get about 100-200km of water, then "heavy ice" gradually merging with the rocky crust of an aquatic super-earth. (See also "Neptune's Brood" and Eliezer Yudkowski's more formal numerical treatment of this situation.)


Since we are mentioning alien biochemistry, what about mixed oxygen/chlorine atmospheres? Or slightly more sinister, could an organism be engineered to photosynthesize chlorine as well as oxygen from seawater?


No one's pointed out that you can start fires electrically, and there are lots of biological examples of electric field sensors and quite some number of electric field generation.

Just because we don't have electric octopodes doesn't mean there couldn't be any, or that a terrestrial one couldn't start fires. Geodesic cartilage, exapted siphon to aspirate with, I'm pretty sure there's a way to grow a turbine to pressurize spiracles if you don't expect them to last, too.


"is it possible that the wavelength of light that chlorophyll is optimally tuned to absorb is actually related to the solar radiation output peak about 1-3Gya ago (or whenever modern chlorophyll first evolved) rather than today's?"

Yes! And also, the atmosphere was different then and might have absorbed different wavelengths. People claim the atmosphere used to be mostly CO2, NH3, and water vapor, which likely wouldn't have much effect. But they could be wrong.


It's a good point, but electrically started fires have the same issue that friction-started fires do: you have to get a lot of energy at a small point to heat the tinder enough to ignite it. That's not quite what electrogenic animals do, but it might be possible. The real problem is that, AFAIK, all electrogenic animals are aquatic, and their systems are evolved to work in water.


"Describe your alien."

Centaur. Elephant with 2 trunks. Whatever alien is chosen, it must have more than one dexterous appendage. Number of legs most likely to be 4


Beetles using hydrogen peroxide


Darn it, your blog at my complex answer. Here's the simpler one:

Wood literally embodies some really neat tricks, and that's why I think it's likely to evolve every place a land organism photosynthesizes in an oxygen atmosphere. Here's the deal: a) photosynthesis is really good at generating surplus carbon. When I worked on a computer model of plant growth, the first problem I had to solve was keeping the plant from fixing more carbon than it had biomass to use it. Seedling plants are photosynthesizing monsters, do to their small surface area/volume ratio. Surplus carbons isn't that useful. Cells run on ratios of nutrients (known as the Redfield ratios in algae), and surplus carbon is a waste material, perhaps a poison. Plants deal with it in part by creating cell walls on the outside of the cells that are composed of carbon-rich molecules (starches, celluloses, lignins, etc). b) wood is a great use of surplus carbon. It's dead, composed of cell walls, and it makes a wonderful support structure. Better yet, if it's made out of conduits of xylem (which aren't syncytia, but are rows of dead cells with their ends perforated) then this inert support tissue also acts as a passive water transport structure. Since plants compete for light, having a dead support structure at the core of the plant means it can grow much bigger than it would be able to if all of its tissue was alive. c) as a result, wood-like and treelike structures have evolved at least six times in plants: lycopods, calamites, tree ferns (perhaps several times), conifers (which gave rise to angiosperm woodiness) and palms and bamboos, which independently evolved wood after evolving from an aquatic ancestor which had lost the ability to produce wood.

So yes, I think wood is likely on an alien planet that's Earth-like.

As for why there are generally non-photosynthetic animals and generally photosynthetic plants, it comes back to that whole surface area/volume thing, plus the fact that trees (and to be fair corals, which photosynthesize in a plant-like way), have both figured out that the best way to monopolize the light is live on the outside of a dead structure that holds them above their competitors. With trees, that dead structure is the wood inside them. With corals, it's their calcium carbonate skeletons. It's a great trick, but it makes it hard to move. Moving animals require a body that's mostly or entirely metabolically active as well as adapted for movement, which means they have higher demand from the inside, and less surface area exposed to the light. With a few interesting exceptions (some nudibranchs and jellyfish), animals don't photosynthesize, at a guess because the metabolic benefits are more than outweighed by the radical constraints on body size, shape, and behavior from staying lit up.

If a planet had a much brighter sun, perhaps the balance would shift and there would be more photosynthetic animals, but that brings its own problems, such as the much shorter life of brighter suns.


"photosynthesis is really good at generating surplus carbon"

So what we need to figure out is an alien world whose primary biochemistry is skewed toward surplus production of some other waste that has tensile strenght. Isn't "silicon plus something" equal to "semiconductor"? So could this not be the basis of an alien critter's metabolism? From this, what would you need to generate enough energy to fabricate products?

One of the Google prizes this year was for a flashlight based on power produced from a 5C difference in temperature. That seems pretty efficient ... although I've no idea how much total energy you'd need to achieve lift-off/space flight.


Starting fires: on the old wooden whaleboats, the (presumably hemp) harpoon line was wrapped around a big wooden stump, and allowed to run if the whale took off. They had to have a bucket of water standing by to stop it bursting into flames from the friction.

An elephant could do that. The elephant wouldn't even have to be the smart one: and if you were using something as big as an elephant for a beast of burden, you might very well do this by accident one day. We can argue about the type of limbs you need to make rope, but that's just a for-example. The point is that using reciprocating action to start a teeny little fire is just because humans don't have access to the brute strength to do it any other convenient way.

Some plant materials will spontaneously combust in fairly simple conditions. Linseed oil on a rag (or other porous substrate with lots of surface area) comes to mind. I know there are others. Someone mentioned bombardier beetles, but there are entire families of millipedes that produce highly-volatile compounds (the worst of them are, like the bombardier's ingredients, stored in separate chambers and combined on the way out).


That last post should be signed Chris L. One day I'll remember that wordpress doesn't do that...


A resin-coated stump does seem like a reasonable way to start a fire, so that is one good possibility. The firesaw from the deep. Excellent!

As for silage and linseed-rag oil fires, as I understand it, the problem is that the ignition is very unpredictable. It may take hours (or days) to ignite, or it may not ignite at all. Compare that with 5-10 minutes for something like a bowdrill. IIRC, people studied linseed oil and such back in WWII to see if it could make a good sabotage weapon, and it was never weaponized. The real issue is that it's an unpredictable danger, not a predictable ignition source.


is it possible that the wavelength of light that chlorophyll is optimally tuned to absorb is actually related to the solar radiation output peak about 1-3Gya ago

The sun's color temperature is currently about 5800 K. A color temperature of 4200 K results in peak irradiance around 690 nm (chlorophylls peak at 680 and 700). If you look at the blackbody radiation curves, such a drop in temperature easily cuts total irradiance in half.

I don't know much about stellar evolution, but that doesn't seem terribly likely.


Source: Wikipedia, Faint Young Sun Paradox"Early in the Earth's history, the Sun's output would have been only 70% as intense as it is during the modern epoch. In the then current environmental conditions, this solar output would have been insufficient to maintain a liquid ocean. Astronomers Carl Sagan and George Mullen pointed out in 1972 that this is contrary to the geological and paleontological evidence.

"According to the Standard Solar Model, stars similar to the Sun should gradually brighten over their main sequence lifetime. However, with the predicted solar luminosity 4 billion (4x10^9) years ago and with greenhouse gas concentrations the same as are current for the modern Earth, any liquid water exposed to the surface would freeze. However, the geological record shows a continually relatively warm surface in the full early temperature record of the Earth, with the exception of a cold phase, the Huronian glaciation, about 2.4 to 2.1 billion years ago. Water-related sediments have been found that date to as early as 3.8 billion years ago. Hints of early life forms have been dated from as early as 3.5 billion years, and the basic carbon isotopy is very much in line with what is found today. A regular alternation between ice ages and warm periods is only to be found occurring in the period since one billion years ago."

5800*0.7=4060 K, so 4200 K isn't out of the question. Sadly, I don't see that they defined what "early" means in this context.


Color temperature isn't linearly related to total irradiance. Check out the black body curves in Wikipedia; the total incoming energy is proportional to the area under the curves. Eyeballing it, going from 5000K to 4000K reduces the incoming energy by about a factor of 3.


Not only is colour temperature not linearly related to total irradiance, but total irradiance is linearly related to total surface area. The Sun's temperature changes very little through its main sequence life – its increase in luminosity is almost all driven by the fact that it gets larger (more massive stars actually cool as they age, but they also get brighter overall, because of the increase in size). You can't blame chlorophyll's absorption spectrum on any change in the colour of the Sun.


Thanks for that: Your para 1 agreed.

Para 2 - Thanks again. Being from Dumbarton, and an ex-member of GUGS, I'm more than just passingly familiar with both caldera plugs and shield plugs (there are exposed examples of both visible from most of the town given a location that has a clear sightline in the correct direction. They can be reached by a 30 minute walk from most places in the town). Boulder fields over igneous rock often represent glaciation effects and don't tell us much about the base geology.


The other factor affecting chlorophyll's absorption peak is of course the question of which wavelengths of solar radiation are least absorbed by the atmosphere; evolution will favour chlorophylls that are most efficient at converting sunlight into usable energy, and this is factor not only of wavelength but of intensity reaching ground level. IR tends to get absorbed by water vapour; UV is also absorbed by air, so presumably there's more to it than just the sun's black body temperature in a given era.


Here's a simplified explanation about one claim for photosynthesis.

They assume that another photosynthetic pathway developed first, that used the green light. Then the chlorophyll approach evolved to use the light that was left over, the blue and red.

I find this kind of plausible. There would have been no selection against chlorophylls that absorbed well in the green as well as the red and blue, but not much selection for them either. So it isn't implausible that something which met the selected criteria well without meeting extra criteria might have won that competition.

The second issue is why the green hole in the spectrum has only been partially filled. Probably plants do not monitor chloroplasts to see how well they photosynthesize, and do not choose better chloroplasts to preferentially go into seeds. So if a chloroplast gets a rare mutation that helps it photosynthesize better, and there are N chloroplasts in the cell, then its effect on the cell is 1/N as big as the effect of the mutation, and the effect on the whole plant is tiny. Then if the cell happens to be one that produces a seed, the chance is something like 1/N that the mutant chloroplast is not lost the next generation.

Still, the claim that land plants are seldom limited by available light is clearly wrong. Given mutation that affects photosynthesis and some way to respond to selection, I'd expect changes.

There's a whole lot of research I had been completely unaware of, about other molecules in plants that absorb light and result in photosynthesis. As a first approximation I imagine something like this -- beta carotene absorbs green light and emits red light that chlorophyll can use. But I have the impression the actual mechanism is far more complicated and not well understood.


Here's a solar spectrum with corrections for air absorption:

The peak is still in the green, but the top is a lot flatter. A lot of the dropoff in the blue and green region of the spectrum is due to Rayleigh scattering, which may be significantly anthropogenic (fossil fuel derived gasses are major scatterers). Also, the higher in altitude a plant gets, the more the solar spectrum skews blue.


Not quite true. Conventional chloroplasts top out at about 20% of full sunlight, although in part this is driven by the amount of CO2 that Rubisco (ribulose-1,5 bisphosphate carboxylase oxygenase) has available to it. If it runs out of CO2, it starts reacting with oxygen, and the chloroplast has a system called photorespiration to capture these reaction products and recycle them into CO2--but it's wasted energy. In fact, some scientists think photorespiration is a check to prevent system overload.

As a side note, the variant C4 photosynthesis system basically works by increasing the CO2 concentration in chloroplasts, but it does that by having some cells photosynthesize while others nearby feed them extra CO2 attached to a four-carbon molecule. So there's a tradeoff in C4: the plant can operate at higher light levels, but a good chunk of its surface is devoted to boosting the CO2 around chloroplasts in other cells, not to directly fixing carbon for the use of the plant. In a high light environment, this is a worthwhile tradeoff, because it boosts overall photosynthesis above 20% of ambient light (IIRC, up into the 30-40% range). In a low light environment, it's not. Plants like sugar cane and maize are C4 plants, and C4 is the kind of thing you find in prairie and savanna grasses, not in the shady understory of forests. It's evolved numerous times.

But I digress. The basic point is that old-fashioned photosynthesis is quite well-adapted for partial sunlight, and in fact, plants have a number of mechanisms for dumping the energy from full sunlight so that they don't fry the leaves. These aren't always successful, as leaves can be sunburned, but they exist.

I was taught that a lot of this can be traced back to the dimmer sun that photosynthesis first evolved under, and that's probably true. Rubisco doesn't seem well adapted to modern conditions. That said, for a plant, the cost-benefit ration is skewed. The downside of not photosynthesizing at all is worse than the upside of photosynthesizing too much, especially if we go back to first principles and talk about algae in the ocean that have to deal with dim underwater light. After all, if you're given two choices: adapt to not die in low light or adapt to create a surplus in high light, you'll adapt to not die, because there are plenty of times when there's light or no light available, especially if you're a cyanobacteria growing under the dimmer light of the early sun in an ocean with other cyanobacteria.


Speaking of underwater conditions, water is blue. Under more than a few cm of water, the available energy for chlorophyll photosynthesis is significantly reduced compared to a hypothetical green-absorbing photosynthetic pathway.

I think comment #95 got it right, that Earth-style photosynthesis resulted from evolutionary lock-in of a suboptimal system.


Going back to third-generation stars...

As this would skew the proportions/relative distributions of elements toward heavier elements, there would be much less free hydrogen, oxygen, nitrogen but much more lead, bismuth, tellurium, etc. So life would be based on elements lower down the table of elements. I'm guessing that this would impact the speed/rate of chemical reactions. (I don't know whether lower atomic number elements tend to be more or less reactive than their heavier sibs.)

Or, maybe stars dying/rebirthing change the proximate background radiation which might be the catalyst for life-creating reactions.

Then there's the dark matter part of the universe ...


"Conventional chloroplasts top out at about 20% of full sunlight, although in part this is driven by the amount of CO2 that Rubisco (ribulose-1,5 bisphosphate carboxylase oxygenase) has available to it."

Sure, so imagine a world with no free oxygen, with presumably a lot of CO2. Maybe a lot of ammonia and/or CH4. The tradeoffs might be different.

"The basic point is that old-fashioned photosynthesis is quite well-adapted for partial sunlight, and in fact, plants have a number of mechanisms for dumping the energy from full sunlight so that they don't fry the leaves."

Yes, and I want to think that a lot of understory plants could be limited by light. They grow slow when if they had more light they could grow faster. Maybe in reality they're more limited by the root warfare etc, "Forest understories receive less intense light than plants in the canopy and such light as does penetrate is impoverished in wavelengths of light that are most effective for photosynthesis. Understory plants therefore must be shade tolerant—they must be able to photosynthesize adequately using such light as does reach their leaves. They often are able to use wavelengths that canopy plants cannot."

It would make sense for them to be better at using green light, but when I dug a little bit more what I found was far-red light used which the dominant plants couldn't. This is all new to me.

"I think comment #95 got it right, that Earth-style photosynthesis resulted from evolutionary lock-in of a suboptimal system."

That seems real plausible to me -- it happens a lot. When I try to look at the details I'm not sure what would have been optimal in the old days, though. I'm not easily finding ammonia absorption bands (maybe there aren't any in the visible spectrum?) and when I look for CO2 absorption I find a morass of climate change deniers drawing random climate-change denial conclusions.

Guesses about the composition of the pre-oxygen atmosphere are probably unreliable. Living things would have done best to produce whatever waste materials they could pump away the easiest, which would lead to a big variety of waste products in the atmosphere.

Maybe somebody has actual evidence about that, but it was a long time ago.


@139 I suggest that you consider the thermodynamics of any ammonia or methane based system and compare it to the available energy your system can absorb. The Rubisco reaction is thermodynamically permitted (although the actual Free energy data is not easily available.) Ammonia has some prominent absorbtion bands in the IR region. a sparse set of UV absorbtions but really none in the visible region(given it is transparent this is not a surprise.) Would there be sufficient energy in the IR region to drive a photosynthetic reaction? I assume that the ammonia rubisco would be catalytic and thus, if the rection isthermodynamically allowed any kinetic problems could be overcome


Actually, IIRC, understory plants get by on far-red light and on sun-flecks. Thing is, they're adapted for low light, and if they are suddenly exposed to high light, their leaves fry. They may be able to recover and put on new high-light leaves, or they may not. With the sun flecks, they may get enough photons to start photosynthesizing, then get a few more later to finish the process.

BTW, when I say adapted, partially that's by evolution, but partially that's by development. Plants are far more plastic than animals, and plants can produce sun leaves and shade leaves that are structurally very different, and don't work well (or at all) in the wrong light environment.


"I suggest that you consider the thermodynamics of any ammonia or methane based system and compare it to the available energy your system can absorb."

I get the impression I said something I didn't intend to.

Various people claim that before photosynthetic plants produced so much oxygen that much of out atmosphere is O2, that the atmosphere was different. They argue that in place of O2 we had a lot of CO2. In place of N2 we had a lot of NH3. Plus a lot of water vapor in the air.

Whatever was in the air would get to filter the light before that light reached early photosynthetic organisms. But it isn't clear to me what was actually there. CO2, NH3, and H2O were probably all there, but there was likely a lot else too, and the concentrations would depend on things I don't know.

"Actually, IIRC, understory plants get by on far-red light and on sun-flecks."

Yes. If they could evolve to get more energy, they might do better. Like, they're probably involved in ferocious root warfare, but if they had more energy they could devote more energy to that.

I'd expect there's pretty much green light just waiting to be used, but they haven't learned to use it. I don't know why. But then, lichens or bacteria of some sort could evolve to use it, and I don't see that they have either. It looks like it just doesn't get used. Maybe I overestimate the benefits.


Bacteria and lichens are stuck using very local resources, and they're especially limited by how much water they can get. Big plants can exploit resources over a larger area.

I'm not so sure why you're attracted to "ferocious root warfare." Certainly plants can compete for resources, but for a lot of plants, they get their nutrients through mycorrhizal fungi, not roots. It's a lot more useful to think of roots as foragers in a soil environment where they have an effective detection range of zero for all poorly-soluble nutrients (meaning they have to be in a nutrient patch before they realize that the patch exists). Some forms of competition make sense in such an environment, but many do not. Why fight for a patch of turf that has nothing useful in it?

As I said, the cost-benefit calculations can be very asymmetric: when the downside of a choice is dying, while the upside is accumulating a surplus, most organisms (including humans) choose to minimize their chance of dying, rather than going for a surplus at the risk of death. This can play out in photosynthesis (where plants often go for a survivably low level of light, rather than trying to max out their photosynthesis at high risk), and it can play out in human politics (where people will put up with horribly corrupt governments if the alternative is dying).


Ms. Bear?....


I'm afraid we scared her off, guys.


Shucks, sure looks like we did. On the other hand, we kids seem to be playing happily with ourselves, with no one screaming or pulling each others' hair, so hopefully she's off getting some real work done :D


"Bacteria and lichens are stuck using very local resources, and they're especially limited by how much water they can get."

Sure, but if they sometimes colonize places where light is limiting, they would benefit by using green light if they could find out how. Probably it doesn't happen, or possibly we haven't noticed.

"I'm not so sure why you're attracted to "ferocious root warfare.""

I don't know much about plants. If plants in low-light areas have even more trouble getting minerals, so that getting more energy just does not help them, then they don't benefit from using extra light. The green light has more energy per quantum than the far red light and originally there was more of it, though some gets absorbed by the first plants to get the light. If less of the unused red light gets absorbed, maybe it's a better choice and maybe it supplies enough energy by itself.

In the abstract, it's a mistake to assume that anything in particular will get optimized. Sometimes things get stuck at a local optimum. Sometimes there's no way to get from the genes you have to the genes you'd need. Plus the search space is vast and populations are small. But it's also a mistake to assume that something is not optimized when we don't know what is being selected.

It should be possible to collect the energy from the green light. It gets done, anaerobicly. There are variant cholorophylls that collect other light. There are a variety of plant pigments that absorb other light and somehow forward some of the energy to photosynthesis. Why not this too?

And at this point my answers are:

  • Maybe it just hasn't happened because evolution is inefficient.

  • Maybe it wouldn't be selected if it did happen, because there's no ecological niche available for plants that did it.

  • Maybe it does happen and I haven't noticed. I can find lots of graphs showing what light gets through the first layer of leaves, and no graphs showing what gets through the last layer.

  • As so often happens, I wind up arguing from ignorance. I don't know what's really going on and probably nobody else does either.


    Don't worry, I think she's just busy -- having announced a new multi-book deal for a space opera trilogy, and a new UK publishing deal, in the past couple of days!

    (I am on a train from Poland to Berlin; blogging will resume when I get home, no earlier than tomorrow.)


    Personally, I find the idea chlorophylls evolved to vbenefit from the gaps in the bacteriorhodpsin absorption spectrum quite convincing, but I'd like to ad some tidbits.

    First of, little oxygen on an early earth means also no ozone; this would lead to quite some photolysis of water to hydrogen and oxygen (see LITTLE oxygen, not none), second of life might only be possible somewhat lower in the oceans, so we might need to take water absorption into this.

    Second of, there might be some mechanistical constraints; it seems the high energy photons of the blue absorption peak are not directly used, but siphoned into the red band. A notable peak in the green spectrum would indicate another energy level the molecule could take, and there are some possibilities why this might not be that interesting; also note chlorophyll is somewhat phototoxic like some other pigments of its wider family (I'll come to them later), so having a molecule that is highly absorbing in the most relevant spectral region would put undue stress on the cells.

    Third of, maybe we should not wonder how ill suited chlorophylls are but think of them as the best evolution could get at from a certain starting point, e.g. historical constraints. Chlorophylls are members of a wider family of organic pigments, lets call them the porphyrins, which is not that correct chemically:

    Those include the heme group of hemoglobin, cytochromes etc., cobalamin etc. And it seems like those have been going for quite some time, there is a related molecule in some archaea:

    The retinal of bacteriorhodopsins is derived from another big family of pigments, the carotenoids.

    Now if we look at the absorption spectra of other porphyrins, most of those have a peak high in the blue spectrum, the Soret peak:

    We could move that one into the green spectrum, but that would mean a bigger delocalised electron system, e.g. more double bonds, and even then we might not be able to use the energy. The red peaks in chlorophylls are the Q peaks, and while the Soret peak is related to delocalised pi electrons, the Q peaks are a somewhat different story:

    They are also somewhat specific for chlorophylls, so they are likely quite involved in the actual mechanism of photosynthesis. It might be possible to move the Q peaks into the green area, but it also might be not. If we look at different chlorophylls

    some bacteriochlorophylls seem somewhat better suited for the green area. It might be interesting to look how bacteria with those differ from the usual chloroplasts, sine endosymbiosis happening is not that rare:


    Para 1 - Colour me interested.

    Para 2 - Oh yes, and in this too. Have a good trip, and trains are another of my many many interests.


    Thank you, Trottelreiner! I like to think I can make reasonable guesses from a superficial knowledge, but it's awesome to see a master at work.

    "First of, little oxygen on an early earth means also no ozone; this would lead to quite some photolysis of water to hydrogen and oxygen (see LITTLE oxygen, not none), second of life might only be possible somewhat lower in the oceans, so we might need to take water absorption into this."

    Without a thorough lit search, I have a prejudice that people have probably assumed early atmosphere content more than measured it. There's proof there was very little O2, not so much proof about what was there instead. The assumption is that it was like what comes out of volcanoes, after the most soluble parts equilibrate in the ocean. If you asked me for a better assumption I'd have trouble finding one single alternative I'd argue was better, but I don't have much faith in this one. If there was a lot of life affecting things, the actual atmosphere could be some witches brew that would be hard to predict.

    So we'd have absorption of visible light and UV not just by water, CO2, maybe NH3, CH4, etc but also by whatever else was there. Some of that might be predicted by the insolubles that precipitated out, but that wouldn't be a trivial task.


    So far as I know, there are three main sources of information on early Earth:

    One is geology. Most or all of the rocks that are a billion years old or older are heavily metamorphosed, which means that samples of primordial chemistry are stuck in the center of diamonds, zircons, and the like, or are have been cooked for a billion years or more (which is what metamorphic rocks are).

    The second source are experiments like the Miller-Urey Experiment, which attempt to replicate the conditions on early Earth in an attempt to understand how life started.

    The third source is basic chemistry, which inspired James Lovelock. For instance, we're pretty sure that molecules like CH4 are unstable under UV light, and so forth, so postulating an atmosphere rich in CH4 is unlikely. Similarly, Lovelock noted that life seems to promote far from equilibrium chemistry, such as the oxygen currently in our air. It's reasonable to guess that Earth's atmosphere before life started messing with it was a lot closer to chemical equilibrium than it is now. This would suggest that the predominant gases in that atmosphere were stable things like N2 and CO2.


    The compounds produced by the Miller-Urey experiment were a veritable gloopfest, and it wouldn't surprise me if at their peak they strongly affected the available spectrum.

    On the other hand, the operative term there is 'at their peak'. I'm under the impression that chlorophyll came along a lot later, in which case those free compounds would long since have been metabolised by the first forms of life before those had to find other sources of energy.

    But it's difficult. If that first energy source was the metabolisation of HS from undersea smokers, we might well be looking at deep water spectra.


    "Most or all of the rocks that are a billion years old or older are heavily metamorphosed"

    Yes, you can draw some conclusions from them but it takes a lot of care.

    "The second source are experiments like the Miller-Urey Experiment"

    That gives you an idea whether life could have started here if your assumptions about pre-life conditions are right. If it showed that life could not form here under those conditions then it would mean that the assumptions are wrong or that life arrived here from elsewhere. Since it implies that life could have happened under those conditions, the assumptions could be right but it isn't evidence that they're right.And it says nothing about the changes that abundant life would have made to the atmosphere.

    "The third source is basic chemistry"

    Yes, but that takes a lot of interpretation too.

    "For instance, we're pretty sure that molecules like CH4 are unstable under UV light, and so forth, so postulating an atmosphere rich in CH4 is unlikely."

    This assumes that oxygen was rare in the upper atmosphere in which oxygen was formed by UV, and also that no other UV-blocking compounds were present in high enough concentrations. This was probably true before life. After there was enough bacterial anoxic photosynthesis to convert a whole lot of the ocean's carbon to biomass, would that still be true? Maybe. I doubt there's much evidence either way.

    "It's reasonable to guess that Earth's atmosphere before life started messing with it was a lot closer to chemical equilibrium than it is now."

    Yes, but how would it be after hundreds of millions of years of anaerobic photosynthesis? I figure that's harder to predict.

    It might be interesting to do sort of the opposite of Miller-Urey. Set up conditions that presumably approximate those of ancient oceans -- probably more iron and sulfur and various other things, maybe high UV or maybe not -- and introduce a large variety of anaerobic bacteria trying to avoid modern photosynthetic ones. Give them light and see what kind of atmosphere they create.

    Somebody at a Dupont lab told me about someone who grew E coli anaerobicly in continuous culture, and arranged to extract the ethanol but recycled all the other volatile waste products. He got a mutant E coli that produced only ethanol. Usually E coli is smelly because it produces a wide variety of wastes, but when ethanol was the one waste product in lowest concentration, there was selection to produce more of that and less of anything else. So I would imagine that in the old days they would produce every volatile waste product that they could make a profit on, up to the point too much of it stayed in surface waters.


    So all/most of our oxygen came from meteors/ice comets?

    If so, then to find other 'advanced' life, or where advanced life might come to be, or where the human race could potentially move to, we'll have to look for planets about our size that are directly in the path of large comets. (Or figure out a way to lob large comets at suitable rocky planets.)


    An obvious problem with that idea for Sol system is the "goalkeeper" role that Jupiter particularly and also Saturn take in catching Oort cloud objects heading in-system.

    As for firing comets into rocky (but low atmosphere) planets, as long as we can get the generator plants aboard suitable comets, there's plenty of comet to supply reaction mass for an ion engine.


    I think we're still coming to grips with typical population profiles of solar systems, but my expectation is that Oort clouds and cometary belts are to be expected during planetary formation, and that it's not a case of whether planets are in cometary bombardment zones, it's more one of whether there's anything else like Jupiter to catch them first.

    Or in other words, Jupiter is why we're not a water world. (Hey, we're mostly covered in water.)


    That led me to ask a question. Using the simplifying assumptions that the Earth is a sphere and that the water depth is small relative to the radius I calculated the volume of water needed to be supplied by the planetary bombardment theory at 1_530 million km^3 based on something I've seen claimed that if the planet was perfectly smooth we'd be 2 miles deep in water. That's a lot of comets!


    Regarding humanoid aliens: Convergent evolution is a damned strange thing. What I find remarkable is that the same designs keep popping up in nature. Icthyosaurs, dolphins, sharks, all have a very similar morphology. I find it particularly striking that dolphins have evolved the dorsal fin. That's not simply an adaptation of an existing structure, it's a whole new outgrowth. And the recurrence of certain adaptations removes chance from being the only explanation. Eyes have evolved numerous times, though the count I see varies from source to source.

    What's also suggestive is how there's constant evolution to fill biological niches. We have flying reptiles, mammals, birds, all with adapted forelimbs. We have placental and marsupial wolves. (well, had.) Giant filter feeders have evolved in whales, sharks, and some other giant extinct sea creatures.

    What also kind of bakes my noodle is that mammals aren't the only animals with placenta. There's even a viviparous shark that has something akin to a primitive placenta!

    There's talk that the genetic hardware is all there in the basic kit that all living things share. Every single living thing on this planet we know of is all descended from one original living cell. So if we're not talking panspermia, then aliens would be starting from a different kit, period.

    So I have wondered about there being a great filter about what sort of critters get into space. Being able to control fire seems like a good shorthand. A longer definition might be "physically manipulate the world in order to create technology." I had a set of alien species I'd invented back in high school that consisted of highly intelligent and social filter feeders and bright but sub-intelligent monkey-like companion species. They had a mutualist system where the whale provided a convenient floating home to move from island to island and the monkeys would defend it from predators, remove parasites, etc. Audio communication happened to encode a lot of situational information so a monkey describing something could be in enough detail for a whale to properly appreciate it, painting pictures with words. So the monkeys could essentially operate as telepresence waldoes on land.

    A friend came up with a species, he called it the Schlingpflanze or creeper-vine. They were mobile plants that moved about on tripods. The vine itself was the muscular structure to articulate the legs. The conscious mind worked at a very slow rate so humans walking about were fantastic blurs. The reactive mind was fast and could react in what we would call real-time. If a human attacked a creeper, it would retaliate and the flow of events would percolate down into the vine's awareness. I can't recall if the tripods were woody growths that came from the creeper's own body or if they were constructed from material in the environment. The vines themselves looked like green spaghetti and there was no central part of the body, just a tangle with the vines going every which way. I think they fed by sucking sap from trees and they developed the walking system because trees could be rather far apart. So I think the evolutionary history was that they were a tropical creature that adapted to crossing empty expanses.

    For something like precision manipulation, fire-making, etc, the vine would decide what it needed to do and essentially program those steps into the reactive mind, then things would play out from there. Needless to say, the creepers weren't great at handling surprises so they were very cautious about how they proceeded. Anything beyond obvious stimulus/reaction would be too much for the reactive mind to handle.

    The creepers could encode their thoughts and memories into nectar and transfer it from creeper to creeper. They find the human way of exchanging thoughts to be horrifically inefficient and laborious and feel very sorry for us. They do envy the speed of our conscious minds but feel that there's just too many drawbacks that go along with it.

    Both of these examples provide counters to the humanoid example. But I wonder just how many times random evolution would come up with the humanoid body plan. That depends on developing tetrapods and how likely was that? With those flying creatures I mentioned, they're all tetrapods. Flying fish and flying squid have hit upon the same strategy while looking nothing alike. Flying squirrels and sugar gilders do look alike. However, both being tree-dwelling mammals, of course they would.


    I've not seen a good alien biosphere described in SF for a while — perhaps the most recent one was from China Mieville. I'm wondering if it's a fashion that is currently out.

    Perhaps we need a new Jack Cohen.


    Pretty interesting aliens you've come up with ... Have you ever tried to figure out how evolution might come up with a flame-breathing critter? The general idea seems that controlling fire is fundamental to developing technology ... but if that fire-making ability is inherent (a no brainer), I doubt that such a species would use it as the basis of their technology. In other words, that species would need some other (fundamental) problem to solve to spur them on to develop any technology.


    It's a lot of comets by today's standards, yes. But in terms of the volume of the Earth as a whole it's almost lost in the noise.

    (I shall carefully not mention Velikovsky — damn, I just did — and his 'theory' of historical era cometary activity. Batshit insane, enough so to make the Scientologists look boring. Did you know Venus is a wayward comet?)


    Well, I spent a lot of time on the biosphere in Scion of the Zodiac, but the story is merely okay, which is why it's self-published. There are three issues there: one is that biosphere construction takes a lot of time, even when you know what you're doing. For example, I was writing about life on the moon of a really big gas giant, and one of the things I had to figure out was what the sky looked like. After all, if you've got a gas giant taking up 17 degrees of sky, the phases of said giant are going to be the major feature that everything sees. I got it right, but it took a couple of days with the trigonometry and geometry and a reasonably large excel file.

    The second issue is that there's a bit of a tradeoff between biosphere complexity and the rest of the story. It's hard to keep the story from devolving into scenery porn, for example, and every word spent on the biosphere is a word that's not put to developing characters or plot. I'm pretty sure this is why writers generally create the plot and the paper over the spaces with whatever comes to hand from recent popular science magazines.

    Third issue is that a good, working ecosystem doesn't really look that alien. When I went back and looked at what I thought of as the great works of worldbuilding (Dune say, or A Door into Ocean), they don't functionally work. For example, sandworms fail in multiple ways (anyone ever seen a drilling machine that big? No? There's a reason for that. Anyone ever seen a giant worm exhaling oxygen? No? There's a reason for that. Anyone wonder why something the size of a decent skyscraper would actively pursue a human for food, even though it's expending more resources catching the human than it would possibly get back? You get the idea), and so it goes. Often, things that are the epitome of cool aren't physically possible.

    Most authors, very sensibly in my opinion, spend their time crafting works that are fun to read, because that's what sells. Someone who spent the effort crafting a really good alien world would have trouble making that effort back in increased sales. The audience for authenticity isn't that big, and unfortunately for everyone, it's hard to make it as cool as a flight of fancy. People will happily read about Pernese dragons flying after thread, but it's a lot harder to sell a story about amphibious dragons who garden swamps, attempt to tame or domesticate everything they come across, think humans make great pets, and help their tame humans survive in what would otherwise be a hostile alien biosphere. Where's the drama and charm in the latter story?


    What's the problem with a dorsal fin? Basically everything that swims fast has one. It's sufficiently advantageous that any evolution towards one would be selected for.

    As for placentae, there are similar structures in caecilians and some reptiles, if I remember right, including all those aquatic mesozoic species (there are fossils of females who died in childbirth). Basically, it's end-point of evolution for retaining eggs internally. In a couple of lineages, there's a pretty good developmental sequence from species laying eggs to species retaining the eggs internally to species figuring out a way to nourish the internally retained eggs internally, which is (crudely) what a placenta is. Heck, even some plants are considered viviparous, in that the baby plants sprout from the seeds while the fruit containing the seeds is still attached to the parent.

    As for things like DNA, RNA and porphyrins, I suspect they're pretty widespread on other worlds, because they're really useful chemicals for life. There's a difference, though. While DNA may be a widespread data recording molecule, there's no reason (AFAIK) to assume that our genetic code, the assignment of amino acids to particular triplets of DNA, is anything other than random. Alien genetic codes probably won't look anything like ours, which means that things that exploit DNA sequences, like viruses, won't be able to jump from aliens to us.

    As for evolution of the human form, that's not to awkward either. It goes something like this: --Nature seems to favor fewer limbs for terrestrial existence. This is best seen in arthropods, where there is tremendous variation in the number of legs, but the most common groups (animals and insects) went in for fewer limbs. Four to ten limbs seems optimal, and the largest animals all had four limbs. It's not clear why, but it makes me think that four limbs is functional, rather than being a random artifact of our evolutionary history. --five fingers: early land vertebrates played with all sorts of finger numbers, but five won out very early on. Later animals reduced that number to one (as in horses), but five is still the most common number. While I don't think all aliens would have five fingers, it would take special pleading to give them, say, seventeen. --bipedalism: there's a neat and poorly known rule called Carrier's Constraint. Basically, quadrupedal animals that run are kind of stuck, due to their musculature for breathing. If they're built like lizards without a diaphragm, they either have to hold their breath while they run (which is what most lizards do) or employ a gular pump (which is what monitors do) to pump air down into their lungs. Animals with a diaphragm and the right musculature can gallop, but when galloping they are limited to taking one breath per stride, which imposes limits on their endurance. One of the best ways around this problem is bipedality. If the animal is only running on its hind legs, Carrier's constraint no longer applies, and it can breathe however fast it needs to while running, although it may run at a slower speed than a quadrupedal gallop. Dinosaurs figured this out a very long time ago, which is one reason why they've hung around so long. Not a lot of mammals have picked up on bipedality (humans and kangaroos come to mind), but it does have some substantial advantages that favor can its evolution. --Fire: fire does have a bunch of adaptive advantages, but there's an argument out there that it promotes brain size. The argument goes that organs take a lot of food. This particularly goes for things like brains and digestive systems, and if you're going to grow one, the other has to shrink. Fire short-circuits this, because you can use fire to effectively externally digest your food. If you have cooking, you can get away with a smaller internal digestive system, and that allows for the reallocation of resources to a bigger brain. One could argue that cooking is a per-requisite for large brains.

    Note that none of this precludes an intelligent alien that looks nothing like a human. My point here (as above) is that a roughly human-shaped alien isn't stupid. Note that roughly human-shaped means bipedal, four-limbed, and able to make a fire. This could as easily be something that looks like a bird or a dinosaur as something that looks like a rubber-forehead alien.


    "But I wonder just how many times random evolution would come up with the humanoid body plan,"

    Nobody knows. But here's something I think might be plausible.

    If a being goes forward, then it makes sense it should have a front and a back. And if it's in an environment where it has an up and down, it makes sense it might have bilateral symmetry.

    If it does things fast, it makes sense to shorten the distance between sensory organs at the front and the reactive circuits that decide what to do with that information. So you could have a brain near the front.

    If it needs a high motabolism rate to do things fast, then it makes sense to minimize the number of appendages since they all metabolize. The minimum number of appendages might tend to be two, though things like tongues can matter. Four is a good number too, that allows a little bit of specialization.

    If it's an environment where you need more specialized appendages then that approach fails. So I'd expect it to evolve in relatively small biomes, where there arten't so many species that anything you try to do with adaptable appendages gets outcompeted by something that has specialized appendages which do it better. If the oceans are too big you might get 4-appendage organisms evolving in big estuaries or shallow seas or someplace that's the right size for them.

    So there you've got it. Bilateral symmetry, sensory organs and brain at the front, minimize the number of appendages and give them generalized abilities, and you're almost narrowed down to humanoid right there.


    I realise about the noise; I actually ignored the fact that it's a delta volume calculation and just did nominal area * depth!

    Still being serious, there's also the points of having not 2 but 4 goalkeepers, 3 other inner rocks to share the bombardment (but between the 3 of them they'd maybe absorb half the total?) and which theory do we use for the asteroid belt this time?


    If it does things fast, it makes sense to shorten the distance between sensory organs at the front and the reactive circuits that decide what to do with that information.

    Generally, sensory organs on Earth developed from signal processing cells (nerves, in Earth animals) that happened to be exposed to a useful signal; the rest of the organ developed under the selective pressure to maximize the useful inormation. This implies that generally most of the sensory organs are going to develop near the creatures largest density of signal processing cells (its brain-analogue), more often than not.


    "While DNA may be a widespread data recording molecule, there's no reason (AFAIK) to assume that our genetic code, the assignment of amino acids to particular triplets of DNA, is anything other than random."

    Our genetic code is a gray code. Most single-base mutations result in either the same amino acid or a closely related one. Mostly hydrophilic amino acids are replaced by hydrophilic ones, and hydrophobic with hydrophobic, etc. I'm not clear how you'd get natural selection among genetic codes to result in a good one, but if ours is pretty good that way then maybe others would be too.

    I read a claim that some amino acids tend to be attracted to some 2-base nucleotide sequences. The author wanted to believe that this allowed production of proteins before we had a complicated transcription system evolved to handle that. Reading his claims I felt skeptical but I have no better suggestion.

    [...] it's a lot harder to sell a story about amphibious dragons who garden swamps, attempt to tame or domesticate everything they come across, think humans make great pets, and help their tame humans survive in what would otherwise be a hostile alien biosphere. Where's the drama and charm in the latter story?

    I'd read that. It's a pretty interesting premise, especially if you aren't wedded to the idea of dragons as big scaly boss fights. As for the drama, PvE stories are a perfectly acceptable form: witness disaster movies, some kinds of post-apocalyptic stories, and indeed Pern itself.

    (aside: Smaug is an interesting thing: I'd argue (based on lack of further data points) that he's kind of the tipping point between the "big scaly allegory" thing and "big scaly character". He's still a boss fight, but he has a personality (albeit a flat one), and his body has physical details like being soft on the underside.)

    But yes, being fun to read is the primary qualifier. Some people find worldbuilding fun even sans much of a story, others are just here for the character drama. There are stories where I skip past the character development because it's simply not as interesting as what's going on in the other parts.


    I think I referenced the title in the post you replied to, and it's should be still for sale.


    It's on Bezos' Book Emporium here. And the dragons are very good.


    What's the problem with a dorsal fin? Basically everything that swims fast has one. It's sufficiently advantageous that any evolution towards one would be selected for.

    Evolution usually adapts structures, it doesn't tend to create new ones. Most classic example, if an animal is going to develop the ability to fly, it's not going to sprout wings on its back. Pegasus is technically a hexapod. A flying horse arrived at by evolution would be adapting existing limbs, just like birds.

    So, it's amazing to me how this entire new fin structure sprung from nothing. The flippers are adapted hands, got it. Legs atrophied and are now vestigial bones inside the body. The fluke is a modified tail structure. Got it. But the fin?

    There's some talk on it here. The best takeaway: this is a thing! Sonic Hedgehog Function In Chondrichthyan Fins And The Evolution Of Appendage Patterning

    The hedgehog gene (hh) was first identified in the fruit-fly Drosophila melanogaster in the classic Heidelberg screens of Christiane Nusslein-Volhard and Eric Wieschaus, as published in 1980.[2] These screens, which led to them winning the Nobel Prize in 1995 along with developmental geneticist Edward B. Lewis, identified genes that control the segmentation pattern of the Drosophila embryos. The hh loss of function mutant phenotype causes the embryos to be covered with denticles (small pointy projections), resembling a hedgehog. Investigations aimed at finding a hedgehog equivalent in vertebrates by Philip Ingham, Andrew P. McMahon, and Clifford J. Tabin, revealed three homologous genes.[3][4][5][6] Two of these, Desert hedgehog and Indian hedgehog, were named for species of hedgehogs, while sonic hedgehog was named after Sega's video game character Sonic the Hedgehog.[7][8] In the zebrafish, two of the three vertebrate hh genes are duplicated: shh a,[9] shh b,[10] (formerly described as tiggywinkle hedgehog named for Mrs. Tiggy-Winkle, a character from Beatrix Potter's books for children), ihha and ihhb[11] (formerly described as echidna hedgehog, named for the spiny anteater and not for the Sonic character).


    Third issue is that a good, working ecosystem doesn't really look that alien.

    Which is odd, because it's easy to find human cultures that seem much too alienating to work. Imagine trying to write a piece of fiction where the protagonist is a legit samurai who has no concept of "human rights", "equality", or "freedom". Or a modern Saudi policeman, dutifully chopping off the heads of accused sorcerers every Friday afternoon outside the police station. It's hard to write a likeable protagonist in these situations without making that person the one enlightened individual who's basically a 21st century westerner at heart.


    Personally, I suspect the fans of Game of Thrones would disagree with you, but I get the point. What I was getting at are fire-breathing dragons, sandworms, and other things that generate a "sense of wonder." In reference to the Game of Thrones, I'm talking about that improbable ice wall and the dragons, not the politics. Both can be alienating, but in different ways.

    Once we're in the literal weeds of figuring out what type of photosynthetic pigment a planet's plants have, while their flower-equivalents may be weird, they look just like plants, if we're trying to be realistic. At that point, reader boredom is an issue. A planet with black-pigmented leaves growing under a red dwarf may be cool and fun to describe, but absent some bizarre special pleading, said planet is probably going to be more of a food desert for humans than the Sahara is. If the vegetation in such a story becomes important, the story will tend to veer towards survival. If it isn't, then noting the black-leaved forest that the skimmer zips through on its way to the collect the next plot ticket may be all a writer needs to do. The pilot could even admire the "glittering silver sporophytic sprays on the tips of the maroon feather-oaks" as she zipped by. What more do you need?


    "So, it's amazing to me how this entire new fin structure sprung from nothing."

    Well, but it's a lump of cartilage. It doesn't do anything but sit there and be cartilage. So it seems to me no more amazing than a pointy-ear human. Or maybe a bit less.

    It isn't like a new organ or a new appendage. It's just a change in distribution of cartilage.


    Four to ten limbs seems optimal, and the largest animals all had four limbs. It's not clear why, but it makes me think that four limbs is functional, rather than being a random artifact of our evolutionary history.

    I don't think this argument works. Terrestrial animals have number of limbs ranging from >100 (millipedes) to zero (snakes, etc). Terrestrial vertebrates do have a maximum of 4 limbs (sometimes 2 or 0), but that is because their limbs evolved from the paired pectoral and pelvic fins of fish. If there is an adaptive reason for having four limbs, you need to look for it in the water, not on land. But given the range of limb numbers among aquatic organisms, it looks to me like an accident of history, not a functional constraint.


    "Third issue is that a good, working ecosystem doesn't really look that alien."

    There are lots of good working ecosystems here on earth that look extremely alien. But that might not be the point.

    I think it might be more that science fiction readers tend not to be all that interested in ecosystems. If you have very important details of the local ecosystem built into your story, they won't understand unless they followed those details, and there isn't much cultural background in SF for that.

    So, say you have a world where the atmosphere is about 60% xenon. O2 is lighter than air, CO2 is lighter than air, N2 is lighter than air. H2 is a whole lot lighter than air. Land plants don't need woody trunks to get the first sunlight, they just need CO2 and H2 bladders to float. They have to come down for minerals, though. Sea plants can also float where they are safer from herbivores, except for the ones that can float too....

    You could build something very strange from that. People on the ground surface might build far different structures when at any time a lot of some plant or animal's waste might fall on them. Transportation would be different. Farming might be more like herding. Local people might develop some fundamentally different attitudes, and there would be various tricks they could play on hostile people who weren't from round there, who didn't know how things worked.

    But if you display the different attitudes they're likely to put people off. Characters who don't act human -- meaning 21st century western -- tend not to be sympathetic. It's a great big effort to understand a story like that. An acquired taste. Probably a small market.

    Jack Vance had a lot of peculiar ecosystems and usually the hero passed quickly through them. There would be something interesting, a quick story, maybe the details would matter to the plot briefly, and then he was off to somewhere else. Lots of local color that didn't get in the way much.


    It migt depend somewhat on the Saudi definition of sorcery...

    Also note that you don't have to go to Saudi Arabia for "unenlightened" attitudes; I actually know of one guy whose teaching another was blocked by said pupil's relatives objecting to him teaching witchcraft. The offence? Teaching Wicca? Evolution to Muslims? Doing a seance? Hardly that, just teaching East Asian Martial arts to a kid from an Fundamentalist Protestant community. Make one even more scared of Dominionism...


    Personally, I don't think actively mobile photosynthetic organisms are not that unlikely to evolve; all you need is either a seperation of some resources, e.g. nutrient-poor surface waters and nutrients at a depth not suitable for the usual physiological transport systems, or an extreme environment where the areas suitable for photosynthesis are periodically subjugated to conditions not survivable even with thick exoskeletons and like, e.g. a nearly tidally locked planet where photosynthesis is only possible at dawn, later the water getting either too hot or subjecto to hard radiation.

    Another possibility might be high herbivore pressure, of course.

    One could find precedents for both in terran ecosystems, BTW; a situations of scarce nutrients is at the core of the evolution of "carnivorous" plants, while daily migration is known from phytoplancton:

    Maybe Elysia et al. might be an evolutionary starting point for that:


    Ice walls and dragons have the advantage of a sense of wonder having greater tensile strength than a sense of realism. At least when keeping one's disbelief off the floor.

    And I suppose if you put the black plants under more earthlike light, they'd be blueish, simply because there's less reason to absorb blue light when there isn't much.

    (aside: Ringworld's Children had black plants at one point, but they were clearly artificial)

    (and Scion of the Zodiac is pretty neat so far)


    You hit the nail on the head. The biggest mobile photosynthesizer that I know of is that Palauan jellyfish in Jellyfish Lake, where the jellyfish move to track the sun. I'm not sure how big they get. Bowling ball sized? They're a lot lighter than a bowling ball, of course, and most of the jelly is metabolically inert (that's the jellyfish killer app).

    The ultimate problem for moving photosynthesizers is surface area to volume. If an organism is tiny enough (as with plankton), then it has a high SA/V and it's easy to have the energy surplus to move. It may also be necessary, given that the plankton's local nutrient supply area will be tiny without movement.

    For something that's, say, human-sized and -shaped, it's not possible. We've got around 2 square meters of skin, and (dividing it half because only half can be illuminated), that means we'd generate (fiddling with the math), a maximum at noon in the tropics of around 200 watts at 20% peak photosynthesis, and you can divide that by four approximately to figure out how much you'd get on a daily average basis, just lying flat naked in the sun. You also need about 200 watts to stay alive (2000 kilocalories per day). If you're going to stand up, the amount of light you receive drops off dramatically. This is why a tree that ways as much as a human tends to be taller, thinner, and have a lot more surface area. And to be immobile.

    It might be easier to think of this in terms of solar-powered cars. A solar-powered car a few centimeters across will zip around, possibly even in indoor lighting. A car big enough to carry one person needs to be lightly built and highly aerodynamic if it's going to go any distance, and a solar-powered lorry isn't possible.

    As for high predator pressure, plants are great with that. They go for poisons more than movement, although a few move. They also have a variety of other ways of protecting themselves from harsh environments. The upshot is that running away takes a lot of energy, while adjusting the shape and chemistry of the body does not. Plants generally have bigger genomes than do animals for precisely that reason. They try to survive wherever they're planted, and instead of moving, they grow to where they want to be.


    I went to a fundamentalist middle school. Several of the teachers were worried about my fondness for D&D, thinking that black magic was somehow involved.

    In their defense, if I'd actually had any black magic available to me, they would have had a lot to be worried about.


    The jellyfish don't photosynthesize; they instead have a symbiotic relationship with algae, which themselves photosynthesize. There multiple animal animal species that do this. (There are also some species which eat algae or other plants, and then incorporate the chloroplasts into their skin. This is freaky.)


    Actually, we might argue plants don't photosynthesize either, they are just in a symbiotic relationship with some cyanobacteria usually called "chloroplasts". ;)

    Endosymbiosis happened multiple times, while usual chloroplasts have a double membrane, in some cases there are four membranes or more, indicating a secondary endosymbiosis.

    I'm somewhat with Richard Dawkins on the turning point on symbiosis being reproduction of both partners becoming combined, after that you are already halfway towards organelles...


    What he said :D

    The thing that's interesting is that, even though coral reefs are the largest living structures outside the forests (if you want to call those structures), mobile photosynthetic animals don't get that large. I'm pretty sure that's the ol' SA/V ratio limiting them.


    Thanks! Glad you're enjoying it.


    Coral reefs are mostly comprised of dead bodies; the living ones are at the surface, and are very, very small. And immobile.


    Well, surface area is also important to gas exchange and filtration, so using some of the tricks animal use might help; an example might be some annelid worms:


    Actually, SA/V for capturing light tends to be a little simpler.

    Here, for example, is a picture of the sea slug Elysia chlorotica, spread out so that it can photosynthesize with its incredibly cool stolen chloroplasts (which are in its gut diverticula, which means this mollusc has turned extreme diverticulitis into a profitable symbiosis). This species grows 20-30 mm long and lives near the surface in tidal marshes.

    Still, a complex surface might matter if the organism is running short on carbon to fix. I wouldn't expect an animal to have this problem, but it could happen. Some aquatic plants have feathery leaves for just this reason, and hard-core aquatic plant enthusiasts (they do exist) spike their aquaria with extra CO2 to keep their plants green and happy.


    It's hard to write a likeable protagonist in these situations without making that person the one enlightened individual who's basically a 21st century westerner at heart.

    This tells us more about 21st century westerners than it does about other cultures.

    I have speculated that one reason my near future Scottish police SF novels sold well in the US is because 21st century Scotland is alien enough to feel really alien to American readers, while being just familiar enough for them to be comfortable with it. (Scotland: predominantly white European culture, historically predominantly Christian religious background tending towards atheist, relatively politically left-wing without being (gasp) Communists, relatively liberal, and speak a dialect of "English" so alien that my editors made me neuter the Scottishisms in "Halting State". In other words, it's about as alien as a typical American SF novel set on board a space station orbiting an alien planet. Say, "Downbelow Station".)


    I wouldn't say it feels really alien; I'd say that it feels different enough to be any near-future SF.

    That is, it's just as alien as, say, Blade Runner.

    We Americans are an ignorant lot.


    Shouldn't someone have that little discussion about editors and courage? After all, Sir PTerry got away with a fair amount of dialect in The Wee Free Men and its cohorts, and I suspect he made even more money (at a guess) and didn't scrub the language.


    Terry writes first for the British market, whereas I believe that Charlie's publishers are in the first instance US. I suspect that makes a difference — British readers and viewers are used to dealing with our own regional dialects.


    I've generally found that places like Canada or Britain are more disorienting than truly foreign places. Unexpected behavior is more surprising when you thought you knew what was going on.


    Err, many thanks for the flowers, to translate the German "vielen Dank für die Blumen", but I guess in this area heteromeles is the "master" in question, it has been some years since I saw a biology lab from the inside. Damn, have to hone my skill again some of these days...

    As for early atmospheres, most of my knowledge about this stems from discussions about abiogenesis, well, and some passing interest into exotic critters, AKA archaea. Oh, and the UV-VIS spectroscopy part in chemistry for biologists. So take this with some caution.

    Actually, it seems likely the atmosphere was changed by organisms even before oxygenic photosynthesis, namely by methanogen archaea; actually, there is some talk about the major oxygenation event being not so much a case of the "invention" of photosynthesis but of geological chances dragging those buggers down, google for "nickel famine".

    BTW, I'm not that sure "far from chemical equilibrium" is a necessary indicator of biology screwing with geochemistry, first of, biology is just applied chemistry,

    so for every fact, there might be a somewhat complicated "non-biological" explanation (actually, that was one of the ideas in Lem's "Solaris", the "ocean" was quite actively changing the environment, but biologists explained it as somewhat complicated "chemistry"; the chemists differed...). At the moment, we have an atmosphere far from equilibrium, so it might not be really "stable". Thing is, even without life it might be slow to change, since it's metastable:

    Actually, in one of the examples mentioned on wiki, it's life that's pushing the state to a really stable configuration, which might not be that unusual, just look at destruents and chemoautotrophs.

    Going back to chlorophylls, according to a pdf linked to on

    there are two chlorophylls with one more double bond, chlorophyll c1 and c2, and according to


    the corresponding spectrum shows a redshift for the Soret peak and a blueshift for the Q peaks; also, the Q peaks are smaller than chlorophyll a and b, so that might really be a constraint on chlorophyll-like molecules.

    In the last days, I've been looking for articles on porphyrin spectrums somewhat; an introduction is given in this article:

    Please note that contrary to my first guess, both the Soret peak and the Q peaks are due to the delocalised pi electron system and are found to some degree in all porphyrins; in free base porphyrins there are 4 Q peaks, but if a metal ion, e.g. magnesium is bound, those become two. Binding of an ion also changes the energy of the peaks somewhat. In the zinc porphyrins in this study, the higher energy state peak has a life time some orders of magnitude lower than the lower energy states, if the high energy state is connected with the Soret peak and the other states with the Q states, that might also factor somewhat into the mechanics of photosynthesis.

    As for what happens when we change the central ion, there is a paper about changing magnesium for iron:

    Might be interesting to try this one out with different ions, wavelength of absorption becomes shorter while the peaks stay about the same.

    As for modification of the ring by substituents, e.g. the different chlorophylls, this might also change redox potential somewhat,

    which might be another factor to look at. According to the same paper, blueshifting the Q peak also lessens its intensity compared to the Soret peak somewhat, which might also be a constraint.

    Problem is, we might look at the absorption spectrum of chlorophyll and think it's ill adapted, but there are quite some other factors to look at; absorbing high energies might mean the enrgy can't be used directly but only after passing some transition states, the high energy states might lead to photobleaching etc.

    Interestingly, there is a paper arguing chlorophyll is quite finetuned for actual conditions on earth, namely the absorption spectra is just before an oxygen spectral absorption peak, which would indicate it evolved somewhat after the oxygenation event, the bacteriochlorophylls are somewhat into the oxygen peak, indicating it is them stuck in the evolutionary past:

    Second part here:

    BTW, the group has a database of biological pigments:

    A for the search for extraterrestial life, somebody mentioned polarisation by chiral molecules, seems this is already researched,

    the used CD spectroscopy is somewhat more powerful though:

    Last but not least, a paper about some constraints on absorption spectra of photosynthetic molecules

    somewhat like synthetic biology

    and a paper on the evolution of photosynthesis:

    TLDR, sorry for the link collection, but I guess the evolution of photosynthesis is somewhat complicated, it might not necessarily be an evolutionary lock-in, but there are likely some constraints at work; I guess a green photosynthetic molecule is not necessary, given bacteriorhodopsin, but it seems there are other factors at work, given Haloarchaea not more common, and rhodopsins in general are not that rare for somebody else to reinvent this. BTW, hm, a photosynthetic organ derived from eyes... (guess of mumbling)


    And some people like learning about different cultures (whether because they respect them, or because they like to feel superior to outsiders and their strange ways). They read history or anthropology or old literature or watch TV shows about subcultures. I can't help but think of Jared Diamond's observation that some New Guineans wanted nothing to do with his flying metal bird, and some immediately started to think what they could do if they could just persuade him to let them use it.

    It might be interesting to know if technological neophilia and social sophistication correlate, and how people who like one kind of strangeness but not the other think.


    "Err, many thanks for the flowers, to translate the German "vielen Dank für die Blumen", but I guess in this area heteromeles is the "master" in question, it has been some years since I saw a biology lab from the inside."

    Yes, heteromeles knows far more than I do about botany, from plant physiology through ecology. I'm impressed there too.

    I'm good at evolutionary thinking which requires subtle application of simple concepts, but it can only go so far. I imagined that photosynthesis from green light might be useful enough for some plants to be selected if it could get started, since additional energy is likely to be not a nonlimiting resource. (Liebig's Barrel says that sometimes only the most limiting resource matters. But say the most limiting resource is a mineral that must be extracted. Having extra energy might aid that extraction. Etc.)

    So I reasoned from there.

    Then you started discussing actual pigments and the chemistry of how they might change to absorb those wavelengths. I can sort of follow what you're saying, but I couldn't begin to develop your intuition about what's likely to work.

    I can wave my hands and say I don't know whether it can happen. You reach the same conclusion with impressive detail.

    Heteromeles points out that plants which get full sunlight need adaptations to avoid damage. They probably get as much energy as they can handle already. So I figured that if this other thing has evolved, it would tend to be in plants that specialize in living in the shade of other plants, particularly in such deep shade that most of the available light is green. It could evolve multiple times and still not spread far out of that limited niche.

    To test whether they photosynthesize green light, probably what you'd do is to expose them to monochromatic green light and measure their photosynthesis.

    When I looked for that I got this.

    They tested photosynthesis for red, green, and blue LED colors, adjusting the intensity level to match the absorption. They found the same amount of photosynthesis from all three, proportional to absorption.

    The popular literature talked like only red and blue light could be used for photosynthesis, and I fell for it. But if these guys are right the issue is only that the green light is not absorbed as well. Plants photosynthesize just fine with green light already, they just don't absorb it as well as red and blue.

    So the advantage of photosynthesizing green light better, is only a fractional thing. Meanwhile the far-red light is not absorbed as much by other plants so there's more of it after they take their share. A bigger advantage, as heteromeles suggested.


    Actually, this kind of research into photosynthetically active radiation has been going for quite some time; German wiki has anice graphic about an early experiment on

    English wiki sadly has no picture of the experiment, but an article about the guy:

    Basically, you put a filamentous algae into water, project a spectrum on it and wait for some oxygen searching bacteria to show up; problem is the spectrum is somewhat unevenly distributed, but in a first approximation, it worked out. As visible from the absorption spectra, the "green gap" is partly filled with carotenes, which absorb some radiation and siphon it into the chlorophy systems; this still doesn't really explain the actual chlorophyll spectra, of course.


    I'm a plant ecologist by training, but I certainly had the coursework in plant physiology and plant physiological ecology. There are definitely limits on my knowledge of photosynthesis, especially since I'm trying not to spend hours answering these posts to make sure everything is up to date. Hopefully this has provided more help than confusion.

    The general way I think of the light capturing part of the photosynthetic apparatus is that there are the chlorophylls, which are physiologically expensive both because they have metal atoms in them and because they take metals (notably iron) to manufacture them. Then there are the carotenoids, which are fairly complex pigments that are made from C,H, and O, or in other words, "cheap" atoms that the plant fixes through photosynthesis. IIRC, the plants try to shift as much of the light gathering and protection-from-surplus-light activities onto the carotenoids as possible, because they're physiologically cheaper, so it's easier to make them or remake them as necessary. One theory for why we see fall colors in leaves is that the plants are taking out the metals, N, and P from the photosynthetic apparatus for use elsewhere in the plants, and leaving behind a lot of brightly colored carotenoids as sunscreen to keep the cells from being damaged while the plant clears everything more valuable out of them. If they became sunburned during recycling, they couldn't be salvaged.


    OK, on closer look that paper doesn't say what I hoped it did.

    They used arabidopsis leaves. Their green diodes were centered at 522 so about half of their output would be in the range the carotenoids would absorb. But the minimum absorption was only down to around 50%. On their graphs they measure the absorbed light, ignoring the light that isn't absorbed, so their green lines never extend as far because their equipment doesn't produce enough green light to get as much of it absorbed.

    I wanted it to mean that the frequencies of light that are not used much do get used for photosynthesis to the extent that they're absorbed, so that for example a yellow-green laser could suffice for photosynthesis if its intensity was high enough (provided that intensity didn't make too much heat).

    But instead this is compatible with the idea that the part of the green LED light which is absorbed by carotenoids is just about as efficient at photosynthesis as the red and blue light, while the rest does not get absorbed much at all.

    Englemann's work is certainly suggestive but there could still be a loophole. Like, if his bacteria are affected by a 3X concentration gradient, they might leave a gap even if photosynthesis in the yellow-green area was 30% as high as either side. Now we have the technology to test it more directly without a whole lot of trouble, and it would be interesting if there is some photosynthesis in that area. But it likely wouldn't be publishable if it only confirmed what everybody already believes.


    "IIRC, the plants try to shift as much of the light gathering and protection-from-surplus-light activities onto the carotenoids as possible, because they're physiologically cheaper[...]"

    Thank you! Very clear as usual.


    They found the same amount of photosynthesis from all three, proportional to absorption.

    That paper shows that an absorbed green or blue photon enables photosynthesis better than a red photon, which isn't really surprising. The surprising things about photosynthesis on Earth are (1) green photons, despite being more numerous than red photons, are more likely to be rejected (reflected) by leaves, which is why leaves look green, and (2) green and blue photons have more energy apiece than red photons, and the fact that each absorbed green or blue photon counts only as much as a red photon is actually pretty disappointing.


    It sounds like the photoelectric effect.

    If there's enough light energy in the quanta to catalyze the reaction, then the reaction happens. If there's extra energy the reaction still happens and does not happen more often or harder, it just happens.


    It's similar to the photoelectric effect, in that the absorption bands of the chlorophyll limit the useful energy of an incoming photon. To get more energy out of a photon, the plant would need a different absorber with a shorter cutoff wavelength.

    I used to make photovoltaic cells (more or less, it's complicated) and the more efficient ones would have several layers. The top layer strips out high - energy photons (for a simplified example, let's say 500 nm and below in wavelength); the next layer strips out the medium energy photons (say 600 nm and below) and the last layer takes the red photons (say 700 nm and below). There are a lot of engineering tradeoffs involved in optimizing the design of the multilayered semiconductor structure; the best cells are in the 35-40% of total incoming energy range (and are tens of dollars per square cm).



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