Silicon-based Life with Chlorine

[J'Dona]

I was going to post this on the thread below this one in the Biochemistry section, but I thought I'd make a new thread for it, since it's (I believe) a different approach.

 

I'm planning on writing something big, a science fiction novel based in the future where a few alien races have been discovered (the storyline doesn't matter). One of the races is supposed to be silicon-based. Since I know this is a problem - some scientists go so far as to say silicon-based life itself is impossible - I have to fully consider the biology making them possible. Since this is fiction, I can invent whatever conditions I want, so long as they could possibly exist. Anyway, here's what I've thought of so far, and I was hoping some of you guys could take a look and make some suggestions or tear it apart as appropriate.

 

Silicon-based life has the problem that, in biology, it'll tend to form Si02. How, I'm not sure, as I don't know much about biology or the necessary conditions. I thought that one way around the problem of SiO2 crystals in the bloodstream for this species might be for - in the particular biologies on this planet - the life-forms to breathe in and use Cl2, to react with the SiO2 as so:

 

SiO2 + 2Cl2 ---> SiCl4

 

Since SiCl4 is a liquid at the temperatures in the human body (although possibly a gas in the greater temperatures needed for reactions in silicon-based life), it could be transported easily.

 

However, this introduces more problems, such as that this species could not ingest water without exploding, due to the violent reaction between H20 and SiCl4, and thus the need for a second, independant circulatory system, assuming that internally the two could be separated (since this species will probably be in contact with or use water). Also, this planet on which they form would necessarily be covered in chlorine clouds, which would react with any surface or gaseous water, forming things like HCl (perhaps the species could convert HCl with O2 in the body to form the needed Cl2, of which the amount that does not immediately react with water in the body may be used?) Or perhaps there is a way to isolate SiCl4 in water and prevent it from reacting, or another more inert fluid reaction product between SiO2 and another reactant all together?

 

Another thing I was wondering (probably just wishful thinking, but it would be quite cool) was if this species could incorporate silicon carbide somehow. Such as for bones, or scales (provided the joints are highly lubricated, of course). It would certainly be an evolutionary advantage, but whether the species could ever accompany carbon as well, since carbon would have the habit of reacting on its own, is a major problem here. It would be interesting if they could, but obviously realism is more important than cool factor, despite what Hollywood films might portray.

 

Bear in mind that conditions are pretty flexible... it may not be likely to form, but artistic license allows anything that's at least possible. The star type, mineral composition of the planet, atmosphere, gravity, history, etc., are all changeable.

 

By the way, does anyone know of any protien or amino acid type molecules based on silicon? I can see that the intermolecular forces would be higher, but how else would they be different to organic molecules?

 

If anyone can offer some suggestions, they would be much appreciated. There is still the pressing problem of rigidity (it's necessary for this species to be reasonably flexible in my story), and whereas reactions to remove SiO2, if possible, would help, it's still only a part of the way there. If nobody here has a degree in Chemistry (I sure don't, I've only done A-Level Chemistry in the UK), I could ask my professor, but I'm not sure which questions to ask without sounding like a complete newbie.

[-Demosthenes-]

However, this introduces more problems, such as that this species could not ingest water without exploding, due to the violent reaction between H20 and SiCl4, and thus the need for a second, independant circulatory system, assuming that internally the two could be separated (since this species will probably be in contact with or use water). Also, this planet on which they form would necessarily be covered in chlorine clouds, which would react with any surface or gaseous water, forming things like HCl (perhaps the species could convert HCl with O2 in the body to form the needed Cl2, of which the amount that does not immediately react with water in the body may be used?) Or perhaps there is a way to isolate SiCl4 in water and prevent it from reacting, or another more inert fluid reaction product between SiO2 and another reactant all together?

Maybe it doesn't ingest water. Maybe it lives off some other chemical. I don't know much but I thought I would say something.

[J'Dona]

Thanks for the reply. Maybe more people will post... please guys, if my ideas are pure bolognium, let me know, I don't want to build story history over science that doesn't work.

 

I'm not sure what else this species could use other than water though... I'm looking at this from a chemistry perspective (I know nothing about biology) but I would imagine that if this species were to remain flexible in terms of movement, it would need a large amount of liquid in the body, just like humans are something like 90% water, and H20 seems like one of the only liquids likely to be plentiful enough at this temperature range. I can imagine a species with two circulatory systems (water and SiCl4), but it would be pretty dangerous for them. Those scales I was talking about before would reduce the number of cuts and therefore possible reactions between them, but whether those scales are even possible is something else entirely.

 

Oh, another thing I realised... if this planet really did have chlorine clouds, it would have no ozone layer whatsoever (since Cl2 reacts with O3), so radiation would be higher, thus affecting the entire evolutionary history. Maybe Sayonara can give some suggestions here, since he knows something about evolution.

[-Demosthenes-]

I don't know much about science, I'm only in high school, but I think you are thinking of this as some life similar to our own, but I don't think it will be anything like us. I think you need to think completely indipendently from our species.

I hope to read your book one day. see ya

[NavajoEverclear]

How old are you? Where did you get your education? May I borrow your brain for a few years?

[J'Dona]

Heh, thanks NavajoEverclear, but I wont part with it for any less than a couple trillion dollars, at least. I'm Canadian though. That might be worth something! (another half trillion I'd say?)

 

Yeah, that's a major concern of mine -Demosthenes-. I know life would be much, much different on another planet, and its the single greatest concern I have about creating any alien species. I mean, take Star Trek for example. It's a great series for morals, but you've got hundreds of intelligent species... and every single one either looks like a human, or a human with makeup (Species 8472 excused), and even if this weren't the case... they all THINK like humans. I mean, if humans really discovered aliens there would be some serious communication difficulties, simply because our psychologies would be so fundamentally different (evolving and living on different planets with different histories), that I think calling a Klingon a plausible alien would be an affront to nature. Klingons are humans who uphold honor and war, basically, and you get races like that on Earth even. The formula for species in Star Trek is as follows: Human + useless spot on forehead above nose + outstanding social quirk = Alien! So again, making realistic aliens is a priority for me.

 

The only problem is that humans really couldn't comprehend real aliens at first glance, let alone invent them. I'm more concerned about he biology at the moment, and yes, I am thinking of it in terms of carbon-based life. This is mostly because I haven't any experience with real silicon-based life (nobody does) and I'm trying to set up a new biology from there. I'm trying to imagine how this species would evolve, or even survive, but it's difficult because I know so little about biology (but then, since all biology is carbon-based on Earth, perhaps this is a plus. I do know something about chemistry, at least).

 

I know this sounds naff, and probably evolutionarily unsound, but this species was supposed to have developed in a way that they are naturally altruistic. As in, due to scarcity of resources and the different environments they are in, only a coordinated effort could help them survive (some chemicals are underground, so only certain ground species can reach them and bring them out, and certain chemicals are in the atmosphere or are very erratic and difficult to locate, so airborne species would search for them and alert the other animals). How a species could even evolve this way is unclear... perhaps resources became scarcer gradually and the instincts developed. This isn't really an issue of biochemistry though, and more of psychology.

 

Gah, I'm rambling again, sorry. Anyway, since I want the science in this to be totally accurate, I have to give it some more thought. I asked about any other fluid reaction products between SiO2 and something else, and she says that SiCl4 is the only one. I could work with this... but I've still no idea how anything resembling proteins (assuming they do have anything resembling proteins) could form, and if not, what else?

[greg1917]

Although its an interesting idea, I dont really see it going anywhere because reactions involving silicon aren't at all similar to the massive range of reactions involving carbon compounds. I dont see how you could have a protein or nucleic acid substitue for silicon, or one of the many organic building blocks like isoprene or ribose (for that matter a carbohydrate substitute as well). Some sort of range of membrane systems is absolutely fundemental and life absolutely will not exist without it; proteins or something similar are needed here.

 

I think youll have to employ quite a bit of artistic licence...

[J'Dona]

Hmm... well, 'artistic license' is a bit of a euphmism for wishful thinking (or laziness, in some cases), which is understandable, but I'm not going to have silicon-based life if it's impossible. You make a good point... but I can't help but wonder, exactly how are the reactions of silicon and carbon different, and what conditions might be needed for silicon to form, say, an animo acid? (if it's even possible, which I doubt, and even assuming that other life would need amino acids as such)

 

Maybe they could be carbon-based, but incorporate silicon as well, for skeletal structure or even just to produce energy? I certainly don't believe though that I can only resort to carbon-based life... they've found sulphur-based life on Earth, deep underground.

 

EDIT: Ah, I've just looked it up online. I should have realised, really, that silicon's got a lower electronegativity. I'm not exactly sure how that makes the bonds weaker, but it certainly makes them more polar, so that's why SiO2 is a solid and CO2 is a gas... and the closest silicon equivalent to an amino acid would probably be a crystal. :/

[Skye]

I'd say take advantage of the crystal and semiconductor properties of silicon compounds. Mainly because this is more interesting than an organism that basically has silicon where we have carbon (to me), plus you have alot more information here to use.

[J'Dona]

Thanks for the idea Skye. Well, I've thought about that, and then some... and this is going to be a long post. I think I've thought of a solution that solves both problems (oh the pain!). I'm probably taking this from far too much of a chemist's perspective, so if any/all of this does not work or is even just difficult, please let me know and I'll try to fix it somehow. I repeat again: I DO NOT know very much about biology, and it matters now that this species will use carbon. I think it's acceptable to allow some fuzziness over certain areas, since some areas are simply not know to people now, and can be assumed to be sorted out later, but not anything glaring. Anyway, for those who really want to read it, here we go:

 

 

Imagine the species really does incorporate both silicon and carbon... but the emphasis is on the carbon. That is, they're pretty much carbon-based on the inside, except for their extrenal scales, which are composed of small, lubricated (somehow, probably carbon oils) silicon-based crystals, like SiO2 or, if possible, SiC (that would just be so cool ).

 

Food sources: Their main food sources would probably be a few particular types of complex molecules, containing mostly carbon but some silicon (as their source of silicon), chlorine to assist in the breakdown of SiO2, oxygen, and the water that carbon-based life needs. Their mouth has a windpipe of sorts and a mostly sealed throat. It can hold some of this mixture at the back and filter the needed chemicals through a layer of mucus, similar to that in the Human stomach (which can resist HCl - which these aliens would have in their 'throat' due to the presence of water and chlorine - thus protecting carbon-based tissue below).

 

Complex carbon molecules: The complex molecules would have been formed by the action of a sort of carbon-silicon transitional bacteria in caves underground (carbon-based bacteria, but silicon tolerant), where they are more protected from the chlorine filled atmosphere due to geothermal vents, which flush out any chlorine. These molecules would be similar to protiens on Earth, as they are carbon-based, but would have to incorporate a very small amount of silicon in some way (the silicon would remain in the alien's body permanently once in the form of crystals, unlike organic carbon which needs replacement, so the amount needed is lower). I don't actually know what sort of chemicals these need to be, as I know nothing of boilogy, but they must be similar to those on Earth and therefore feasible. The chlorine would mainly be in the form of clouds high in the atmosphere, and in any surface water.

 

Surface water: Surface water itself would be scarce, however. as this planet is close to its sun and average temperatures are around the 90 degrees Celsius (or 363 Kelvin) mark. Since any ponds or rivers that might form would be erratic at best, the aliens have to (or had to, before they developed advanced technology over millenia) keep moving to keep up with the water, and have to rely on other species to guide them to the next acid rainfall. This brings in the altruism I mentioned before, but whether it's evolutionarily sound I've still got to sort out. I hope it is.

 

The mouth: Anyway, back to the alien's mouth. At the back, they can suck oxygen and Cl2 through another layer of mucus, but this is more of a membrane, and can draw the oxygen and chlorine into their lungs for use (since this is suited for hydrous conditions, the alien is, incidentally, capable of breathing underwater... though I'm not sure if the pressure difference is quite safe). However, they will not always have enough chlorine gas to live off of (since the clouds will be high up), so they need to be able to use HCl as a substitute for at least short periods if they need to, even if it is, in terms of energy used, an expensive procedure. The solution they're 'drinking' at the back will be filled with HCl acid, and the alien is able to secrete a strong organic oxidising agent of some sort (I would imagine this difficult to product... maybe safe within the body but only oxidises in the presence of a catalyst in the mouth?), to liberate Cl2 gas from the HCl. Any gas which does not immmediately dissolve in the surrounding water will bubble out of it and be taken in through the wind pipe, and any H2 gas produce by the oxidation would, I assume, form water with the oxidising agent. The original complex molecules would need to be soluble, but since the mucus itself would prevent H20 from passing through (as in the Human stomach, I'm sure), I'm not sure how they'd get into the stomach. Ummm... perhaps the oxidation reactions, where the HCl concentration would be lowest, simultaneously thin the mucus at the point where the chemials enter the throat, allowing water and these chemicals in, but a minimum of acid. Maybe the whole process could be simplified if someone could explain to me how chemicals like these are separated in humans, like in the intestines or something. I'm totally just making this up right now.

 

Finally, the paragraph ends. I mean... finally, the chemicals reach the stomach, or stomachs, or 'reactors' if you wish. *Sigh*... the squeaking of my mouse is really starting to annoy me (computer mouse, that is). Round two...

 

First stomach: The first stomach is large, and deals with the main digestion. Since this is mostly similar to humans, I won't explain anything here, except that the stomach, instead of containing acid to dissolve the molecules, instead contains a small amount of base to neutralise what's left of the acid from the throat. There's no need for acids to break down the large pieces of food, because they're all in the form of unconnected molecules already. Thus, this stomach is also quite small. The rate at which chemicals come in is slow, and matches the rate out, so the needed storage capacity is very little. At least this means they'll never get obese. Their mouth can hold a lot though (for their size, about as much as their stomachs) so they have some backup.

 

Second stomach: But, this is where the silicon comes in again. During the digestion in the stomach above, SiO2 will be produced, and now it settles at the bottom. The larger stomach is funnel shaped, and the heat and pressure in it forces the solid grit slowly into the much smaller stomach below. I forgot to mention that these aliens are quite small themselves (about a metre tall, though slightly hunched forward and, regrettably, bipedal so as not to disrupt chemical digestoin while walking), so it's only about 5 cm (2 in) across in our terms. Anyway, once the SiO2 filters in, the chlorine that the alien breathed in all those five seconds ago is put in, and viola: SiCl4 is formed! Since a very small amount of water will have gotten in, and water reacts quite vigorously with SiCl4 (hence all the trouble), the stomach itself will be quite hot as the odd reactions occur, but acceptably so (only 450K or so?). Otherwise, conditions in here are anhydrous, and hot. The reaction between any water and SiCl4 wil produce Si(OH)4 and HCl, which after a time are flushed out when the stomach is not digesting and empties (there will be large, mucus-lined arteries to carry the small amounts of solid Si(OH)4 and HCl - which would otherwise be impractical - to come out somewhere down the side of the legs). Si(OH)4 will build up very slowly over time in the stomach, however, and eventually lead to digestive failure and death, this being the leading cause of death before the invention of... surgery.

 

Ok, what else? Hmm... oh yes, excretion. Dang...

Excretion: Waste from the 'hot' stomach is sorted, but what about that from the SiCl4, waste respiration (CO2... they do produce this, don't forget!), or solid/liquid waste? Well, they won't be producing any solid waste (it's all in the form of soluble chemicals, and they're quite hot as well). Liquid waste from the larger stomach is easy to remove... perhaps it can be funneled down the same channel or a parallel one to the other stomach's. Waste gases... they could be removed through gills on the neck or shoulders (this alien will have arms), since it's easy to expel without letting any liquids/acids in. In fact this might solve the pressure problem when breathing underwater; if the alien does 'circular breathing', like some people can, then the pressure will remain constant, so a balance can be found that lets the most air in without sucking too hard.

 

You know what... I think I'm done. Or at least, that's all I'm doing for now. I just spent about three whole hours on this. I'll bet it's all wrong. If anyone's read the entire thing... then wow, I'm impressed. I'm not even doing that after typing it!

 

Given that this jargonic leviathan purports to be scientific, maybe I should have done it in formal style, but then it would have been death to write (and read).

 

Flip. Why do I need to write a book now? I just wrote one!

 

EDIT: This post takes over two screens. I have no life. At least I'm only a college student; I'm not expected to have one.

 

EDIT2: I've just realised that I haven't even looked at what happens to the SiCl4 after... grrr, I don't want to get back into this again after all that. Can anyone think of how the SiCl4 could be used to produce the silicon compundbones or scales, and then the chlorine removed? The SiO2 would likely collect right under the scales, where they are slowly removed as the layer of oil sort of 'bleeds' out. Thus, if they don't get enough of their food the oil flow will stop, and the SiCl4 in the blood will eventually deposit more and more SiO2 under the scales, which is very painful when the crystals get larger. Also, if there was suddenly a wound or tear in the scales, the SiO2 would crystallise around it, 'clotting' it, but then it would take months to fully heal and be fall out.

[J'Dona]

Erf... I hope I didn't scare you guys off. You don't have to leave feedback or anything, of course; I'm really just putting this down for my own record. I promise that my posts will never be this big again (not for a while, anyway).

[budullewraagh]

hmm, what about a respiratory cycle? there's nothing like good ol' adenosine triphosphate. however, a phosphate, sulfate or even borate could work. as for reducing it...try an acid. as for transporting and using that energy.....i have no idea. godspeed.

[NavajoEverclear]

Dude i read in my AP Bio Cliff Notes that Diatoms shells are made of some silicon compound, justa sec let me go look it up . . . . Si02- that'd be Silicon Dioxide right? Maybe the cells of your aliens evolved from something like diatoms. The problem would be i think that would be tougher than plant cell walls, and the reason animals are mobile is cause they don't have any cell wall. But then again theres the venus flytrap and a few responsive plants like that, so maybe the real reason plants don't move is just cause photosynthesis couldn't create enough energy for mobility.

[J'Dona]

That's interesting... so some lifeforms on Earth even use silicon like that? I wonder how they transport it in the body. That's quite helpful as it brings in evolution, thanks NavajoEverclear.

 

Hopefully I'll have more answers tomorrow... I typed up the important notes from this thread (took an hour to edit) for the biology teacher at my college, and she's goign to look through it and get back to me tomorrow. She might be able to help me out on the biochemical side of things... I'll just have to wait and see. Thanks for all the feedback so far guys!