# Straightdope on Silicon-Based Life... **URL:** \ **Category:** Great Debates\ **Created:** [July 7, 2005, 4:40pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471 "2005-07-07T16:40:32Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [July 7, 2005, 4:40pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/1 "2005-07-07T16:40:32Z")
I first heard this subject when I was in high school: hypothetical life based on silicon instead of carbon. But just how likely is it there is such life somewhere in the universe? Also, does anyone know what such life might look like? Would it be similiar to us or much different? And finally, could such life be intelligent like us? Please feel free to add a link to an article that talks about this subject matter. And thank you in advance to all who take the time to reply 🙂 ---
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [July 7, 2005, 4:41pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/2 "2005-07-07T16:41:34Z")
One more question: In what type of environment would you likely find such life? ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [July 7, 2005, 4:46pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/3 "2005-07-07T16:46:15Z")
Silicon chemistry is very different from cabon chemistry, though, despite their continguity on the periodic table. There seem to be a lot more carbon compounds than silicon, and they’re in mre convenient form at our temperature and pressure. Take, for instance, carbon dioxide, which, along with water, is a common product of oxidation of organic compounds. It is, conveniently, a gas. I don’t think that you have analogous oxidation products for silicon compounds and, worse, silicon dioxide is a solid. In his story “A Martian Odyssey”, written back in the 1930s, Stanley G. Weinbaum posits a silicon-based creature who “exhaled” silicon dioxide blocks. It stacked them in pyramids around itself, until it was completerly covered, then it broke out and moved over to begin the pile again. Doesn’t sound practical. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [July 7, 2005, 6:46pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/4 "2005-07-07T18:46:36Z")
> [@Jim B.](#): > > But just how likely is it there is such life somewhere in the universe? Also, does anyone know what such life might look like? Would it be similiar to us or much different? “Likelihood” isn’t the issue. Carbon-based life is very unlikely, yet \*voici, \*here we are! The fact (?) that silicon-based life is less likely doesn’t eliminate the possibility. And how could anyone predict what it might look like? What does carbon-based life look like? Does a t-rex look like a nematode? ---
**Author:** ![kidchameleon](https://avatars.discourse-cdn.com/v4/letter/k/898d66/32.png) [@kidchameleon](https://boards.straightdope.com/u/kidchameleon)\ **Post date:** [July 7, 2005, 7:08pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/5 "2005-07-07T19:08:24Z")
I think the silicon based life bit is based upon merely looking on the periodic table under carbon. While carbon and silicon share many properties, carbon chemistry is far more diverse and complex. It’s just like in _Evolution_ where David Duchovney’s character looks at the periodic table on Julianne Moore’s shirt and declares that since arsenic is ‘our poison’ and the life forms are nitrogen based (something I find more likely than silicon) that that ‘aliens’ poison’ is selenium. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [July 7, 2005, 8:17pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/6 "2005-07-07T20:17:42Z")
Silicon-based creatures do exist, though, and they’re among the oldest species on Earth. The [radiolarians](http://oceanlink.island.net/oinfo/radiolarians/radiolarian.html) are protozoans that live in the oceans and have a skeleton-like structure made of silicon dioxide. They likely never got beyond a few millimeters in size because silicon dioxide makes a pretty inefficient skeleton. They were out-competed by animals with calcium-based skeletons, which were able to grow much larger, support a wider variety of organs, and eventually leave the oceans entirely. ---
**Author:** ![JThunder](https://avatars.discourse-cdn.com/v4/letter/j/e95f7d/32.png) [@JThunder](https://boards.straightdope.com/u/JThunder)\ **Post date:** [July 7, 2005, 8:38pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/7 "2005-07-07T20:38:59Z")
Don’t forget the Hortas. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [July 7, 2005, 8:40pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/8 "2005-07-07T20:40:25Z")
There are several other single cell organisms that use silica skeletons, including diatoms. But this is using inorganic silica as a structural element, not replacing carbon compounds with silicon compounds. The trouble is that silicon is much less reactive than carbon. I think you’d have to have pretty unusual conditions for silicon to form the long chains and polymers that make carbon chemistry the basis for life on Earth. Of course, you could claim that Earth has some pretty unusual conditions too…liquid water exposed to the atmosphere. We just have sample size of one. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [July 7, 2005, 8:41pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/9 "2005-07-07T20:41:33Z")
The big problem with silicon-based life is that, because silicon’s atomic radius is larger than carbon’s, silicon-silicon bonds are significantly weaker than carbon-carbon bonds. ---
**Author:** ![KlondikeGeoff](https://avatars.discourse-cdn.com/v4/letter/k/3e96dc/32.png) [@KlondikeGeoff](https://boards.straightdope.com/u/KlondikeGeoff)\ **Post date:** [July 7, 2005, 10:37pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/10 "2005-07-07T22:37:05Z")
> [@Jim B.](#): > > I first heard this subject when I was in high school: hypothetical life based on silicon instead of carbon. But just how likely is it there is such life somewhere in the universe? Gee, a highly intelligent silicon-based thing is sitting on my desk right now , my computer. 🙂 It seems alive to me. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 7, 2005, 10:42pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/11 "2005-07-07T22:42:47Z")
Isaac Asimov, PhD biochemist, wrote _Planets Have An Air About Them_ in which he explored possible forms of life. His thesis was that there is a minimum energy requirement in order to move around to get food and to reproduce. He analyzed several bases for the chemistry of life that would meet the energy requirements. Sulphur was one, carbon of course and I don’t remember the others, if any. I don’t think silicon was in the running. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [July 7, 2005, 11:04pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/12 "2005-07-07T23:04:23Z")
> [@David Simmons](#): > > Isaac Asimov, PhD biochemist, wrote _Planets Have An Air About Them_ in which he explored possible forms of life. Asimov also touched on the subject in various essays in _The Relativity of Wrong_ and _The Left Hand of the Electron_, including discussions of what he called “thalassogens”, chemicals that could serve as a medium for life. He concluded that water was by far the best and most likely, because of a number of interesting properties, including expanding while freezing. His nonfiction was actually a lot more interesting than his fiction, what with all those noble robots and whatnot. ---
**Author:** ![Jon\_the\_Geek](https://avatars.discourse-cdn.com/v4/letter/j/bbce88/32.png) [@Jon\_the\_Geek](https://boards.straightdope.com/u/Jon_the_Geek)\ **Post date:** [July 7, 2005, 11:16pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/13 "2005-07-07T23:16:35Z")
> [@ultrafilter](#): > > The big problem with silicon-based life is that, because silicon’s atomic radius is larger than carbon’s, silicon-silicon bonds are significantly weaker than carbon-carbon bonds. Agreed, that’s the big problem. Voet and Voet’s _Biochemistry, Second Edition_ has the best treatment of this subject that I’ve seen: > [@Voet and Voet](#): > > Silicon and carbon, being in the same column of the periodic table, might be expected to have similar chemistries. Silicon’s large atomic radius, however, prevents two Si atoms from approaching each other closely enough to gain much orbital overlap. Consequently Si-Si bonds are weak (177 kJ/mol) and the corresponding multiple bonds are rarely stable. Si-O bonds, in contrast, are so stable (369 kJ/mol) that chains of alternating Si and O atoms are essentially inert (silicate minerals, whose frameworks consist of such bonds, form the Earth’s crust). Indeed, science fiction writers have speculated that **silicones,** which are oily or rubbery organosilicon compounds with backbones of linked Si-O units; for example, **methyl silicones,** [image of methyl silicones, with 2 methyl groups on each Si in a -Si-O-Si-O- chain] could form the chemical basis of extraterrestrial life forms. Yet, the very inertness of the Si-O bond makes this seem unlikely. The same section of that text also goes into the problems with boron- and nitrogen-based life, for anyone who’s interested: > [@Voet and Voet](#): > > Boron, having fewer valence electrons (three) than valence orbitals (four), is electron deficient. This severely limits the types and stabilities of compounds that B can form. Nitrogen has the opposite problem; its five valence electrons make it electron rich. The repulsions between the lone pairs of electrons on covalently bonded N atoms server to greatly reduce the bond energy of an N-N bond (171 kJ/mol vs 348 kJ/mol for a C-C single bond) relative to the unusually stable triple bond of the N2 molecule (946 kJ/mol). Even short chains of covalently bonded N atoms therefore tend to decompose, usually violently, to N2. The part of this argument that’s missing from this text: the one example of life we have (by which I mean all life on Earth, since we’re all related and thus utilize the same general chemistry) requires complex molecules such as DNA and proteins, that require the ability to form long chains. I guess it’s possible that there could be silicon-based life somewhere that doesn’t have anything exactly equivalent to DNA, but if you don’t need long chains you might as well hypothesize iron-based life; both iron-based and silicon-based life seem highly, highly unlikely, but we only have the one example of life to base our hypotheses on. Of course, I don’t see any reason not to throw some complete speculation in here :), so… It might be possible for carbon-based life to evolve into carbon-and-silicon-based life, with the long-chain, complex molecules like DNA, RNA, and proteins (or their alien equivalents) linked to a silicate backbone (similar to the methyl silicones in the Voet and Voet passage). I don’t have any numbers handy to back it up, but it seems like maybe such an arrangement would be able to remain stable at higher temperatures than our standard. In fact, it’s possible that life here on Earth started with something similar to such a system (if I understand the [clay-catalyzed RNA formation](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15570708&query_hl=5) hypotheses correctly). ---
**Author:** ![Evil\_Captor](https://avatars.discourse-cdn.com/v4/letter/e/f17d59/32.png) [@Evil\_Captor](https://boards.straightdope.com/u/Evil_Captor)\ **Post date:** [July 8, 2005, 12:44pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/14 "2005-07-08T12:44:36Z")
I believe scientists recently found some organisms living in the salt pan of a California desert that have a really weird biochemistry. They use arsenic to generate energy in much the same way that most organisms on earth use oxygen to obtain food. I doubt that it’s carbon-based, but it definitely shows there are alternate biochemistries out there: [Linky linky link.](http://web.mit.edu/newsoffice/1994/arsenic-1102.html) ---
**Author:** ![An\_Arky](https://avatars.discourse-cdn.com/v4/letter/a/87869e/32.png) [@An\_Arky](https://boards.straightdope.com/u/An_Arky)\ **Post date:** [July 8, 2005, 12:56pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/15 "2005-07-08T12:56:30Z")
> [@JThunder](#): > > Don’t forget the Hortas. No Kill I 😃 ---
**Author:** ![Jon\_the\_Geek](https://avatars.discourse-cdn.com/v4/letter/j/bbce88/32.png) [@Jon\_the\_Geek](https://boards.straightdope.com/u/Jon_the_Geek)\ **Post date:** [July 8, 2005, 2:17pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/16 "2005-07-08T14:17:53Z")
> [@Evil Captor](#): > > I believe scientists recently found some organisms living in the salt pan of a California desert that have a really weird biochemistry. They use arsenic to generate energy in much the same way that most organisms on earth use oxygen to obtain food. I doubt that it’s carbon-based, but it definitely shows there are alternate biochemistries out there: > > [Linky linky link.](http://web.mit.edu/newsoffice/1994/arsenic-1102.html) It’s carbon-based. It still has DNA and proteins, it just uses arsenic where we’d use oxygen. Oxygen is actually highly toxic to many organisms, we’ve just evolved to survive it. ---
**Author:** ![Evil\_Captor](https://avatars.discourse-cdn.com/v4/letter/e/f17d59/32.png) [@Evil\_Captor](https://boards.straightdope.com/u/Evil_Captor)\ **Post date:** [July 8, 2005, 3:51pm UTC](https://boards.straightdope.com/t/straightdope-on-silicon-based-life/311471/17 "2005-07-08T15:51:49Z")
> [@Jon the Geek](#): > > It’s carbon-based. It still has DNA and proteins, it just uses arsenic where we’d use oxygen. Oxygen is actually highly toxic to many organisms, we’ve just evolved to survive it. I meant to say I doubt that it’s NOT carbon-based. Still, it’s got to be a different kind of chemistry – as I recall, humans generate energy by "burning Trisomethingorother down to Disomethingorother,’ combining it with oxygen and using the energy generated by the reaction. I’m wondering if M-13 uses arsenic on the same chemicals, or does it have a whole 'nother set of chemicals?