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Dear All, Rod said his chemistry tutor once said something along the lines of: "if live ever developed on another planet, it could well be silicone based (due to the same number of valence electrons as carbon" As a biologist, I often cringe a little when I hear chemists say something like this. Sure, both Silicon and Carbon have valences of four, but the problem with the silicon idea is that it is kind of like comparing Lego bricks and stone-age megaliths. Yes, both can be used for building and stacking up. But the two are very different in size. Carbon is very much smaller, and complexes more readily with itself. Silicon chain compounds are most commonly in alternating Si and oxygen chains. The oxygen atom spaces out the big Si atoms, letting them chain more stably, but reduces the number of sockets to plug things into, since Oxygen can only hold hands with the two Si's on either side...nothing else. So silicon based proteins, DNA, enzymes, the whole gamut, become MUCH larger and less cheap to build. I can't help but feel that if Si and C based proto-life appeared in the "primaeval soup" the C based forms would so quickly out-compete the Si, that only the C based forms would survive. It is probably pretty safe to assume that if "organic life" with cell membranes, enzymes and proteins ever appears, that it will be based on Carbon. Except on Star Trek! Regards, Neale. -------------------------------------------------------------------- >From Neale Monks' Macintosh PowerBook, at... Department of Palaeontology, Natural History Museum, London, SW7 5BD Internet: N.Monks@nhm.ac.uk, Telephone: 0171-938-9007 --------------------------------------------------------------------
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