I must have read/watched a dozen science fiction stories with silicon based life forms in them (granted quite a few of these were old Star Trek episodes, but what the hey). I vaguely remember from chemistry at school that carbon and silicon are similar because they can both bond with the same number of other atoms. Science fiction writers seem to be claiming that since life forms based on the chemistry of carbon (i.e everything on the planet Earth) are possible isn’t it also possible that life forms based on silicon chemistry can exist? But then again, surely there’s a whole load of silicon on earth, and if silicon based life forms were possible they’d have happened by now. So, over to you, Dopers. Is silicon based life possible? Who came up with the idea in the first place? If it was possible, what would silicon-based life be like and where it is?
Cheers
Wombat
P.S also, what’s the deal with silicon/silicone? Is it another one of those Brit/US aluminium/aluminum things?
Silicon is the element, silicone is a polymeric organic compound of silicon.
You may be able to make “parallel” compounds that substitute silicon for carbon but they’ll have very different properties. While I’ve seen some silicone objects that are , uh, lifelike in certain ways it’s not quit the same thing.
“You may be able to make “parallel” compounds that substitute silicon for carbon but they’ll have very different properties. While I’ve seen some silicone objects that are , uh, lifelike in certain ways it’s not quit the same thing.”
Gosh, I have no idea what you might be talking about (blinks innocently)
Silicon and Carbon are in the same group in the periodic table; this means they have similar valence orbitals and usually compounds that have similar valence orbitals have similar chemical properties. However Silicon does not polymerize nearly as easily or stably as carbon, and that’s pretty essential to the organic molecules of the types we’re familiar with. Intriguingly, Boron compounds actually have some structural complexities that are impressive and seem to me more reminiscent of the interesting things carbon does than the silicon molecules I’m familiar with.
At any rate, silicon based life is a science fiction idea that is pretty unlikely, IMO. Of course, it all depends, too, on exactly what criteria a chemical system has to meet to satisfy your definition of “life”.
It was believed that because silicon and carbon were chemically similar, there could a life forms based on silicon. However, there are problems. If it was in atmosphere, the byproduct of respiration would be silicon dioxide – sand. That would tend to clog up the lungs. There was one gas that would work, but the entire scenario was very unlikedly.
The only real silicon-based life forms I know of were in the movie Starship Trooper – in the shower scene. Or was that silicone?
bear in mind that this article’s two years old, and I haven’t heard of anything since then (of course his work was mainly hypothesis, so there’s still no evidence.)
I do recall that the the first X-files episode I saw had to do with silicon life inside a volcano; probably the writers were vaguely inspired by this gentleman’s report.
Silicon, by itself, isn’t versatile enough to fill all the same roles as carbon, although a combination of silicon, boron, nitrogen, phosphorus and maybe a few other things might do the trick. The problem is that it’d be almost impossible for life to evolve based on such a combination. Remember all those “irreducible complexity” arguments used by creationists? Well, they all become that much more significant when you’re trying to juggle atoms of a half-dozen different elements.
As to the existance of life-not-as-we-know-it here on Earth: Once the first life evolved, it quickly spread over the planet, and immediately started filling niches. Were anything different to arise, it’d be starting at a disadvantage, and would quickly get eaten by the life that was already here. It’s sort of like other software companies trying to compete with Microsoft: Life as we know it has strong monopoly power.
pj, that’s a rather tantalizing link, but I will remain skeptical until I hear his arguments.
Chronos, it’s not clear to me that carbon based life WOULD be in competition with silicon based life or be ABLE to eat it. There would be no digestive physiology for dealing with it. Competition would only exist for material necessary to both types of life.
One of the classic short stories of science fiction is Stanley G. Weinbaum’s “A Martian Odyssey”, published in the 1930’s. The narrator and his martian companion , while wandering through the martian desert, come upon a series of tiny puramids, each broken open at the top. The chain continues as far as the eye can see, with the broken pyramids getting bigger and bigger, until they become huge. The last one in the chain is UNbroken. as hey watch, a huge Something breaks out of the interior, moves a short distance away, then sits back doen and starts producing blocks out of its own body, which it starts piling around itself, forming a new pyramid. It turns out that i’s a silicon-based life form (eating the sand, apparently), and that the blocks are the waste product it’s “exhaling” – silicon dioxide (quartz) instead of carbon dioxide, you see. It’s forced to pile them up around itself, and eventually move on, or else be buried in its own waste matter.
There are a lot of people that take Weinbaum’s story as an elaborate joke (a lot of others take it at face value). In any case, it sows the bizarre results you get from assuming you can simply switch silicon for carbon, keeping everything else fixed. It’s certainly possible to imagine silicon=based life forms, or life based on chlorine reactions, but they’d probably be VERY different from what we are familiar with, and maybe require vastly different chemical situations. (How about silicon-based life in an ocean of hydrofluoric acid – assuming you could come up with a good reason for an HF ocean to even exist.)
You can’t get silicon life out of a direct one-to-one replacement of silicon atoms for carbon atoms; the chemistry is too different.
On the other hand, silicon does produce extremely large molecules in combination with oxygen. Silicone compounds consist of linear Si-O chains with (usually) organic side molecules.
So the question arises, could some analog of carbon-based life be constructed using Si-O chains and sheets instead of carbon compounds? The answer: who knows? Since we only have the one example of terrestrial life, we have nothing else to compare to. One the one hand, you can take the apparent absence of silicon life here on Earth as evidence that it’s unlikely at best. But since no one can say with any great certainty how organic life started from non-living molecules, no one knows what sort of environment would be necessary to give silicon life a chance.
