Silicon/Silicone based life

Just for example, CO2 is a gas and SiO2 can be an amorphous liquid (glass) or a solid crystal (quartz). Just from this example, I would have to say no it can't replace carbon straightaway. Silicilic acid, which sounds hopefully like a liquid or at least water soluble is in fact neither. The closest carbon equivalent to silicilic acid is performic acid (CH2O3), which is readily water soluble. Silicon containing molecules seem quite different than their carbon analogues in almost every sense.Silicon could, however, create long polymers like carbon. But as previous posts have stated, double bonds seem to be a problem as are ring structures. Nitrogen or phosphate, if anything, would seem to be a better bet than silicon in this respect. Just looking through the Merck Index (old 8th edition, 1968) silicon dioxide can be dissolved in hydroflouric acid to produce silicon tetraflouride, a gas. It also says that glass can be "slowly attacked" by heating with concetrated phosphoric acid. The crystal form (quartz) seems impervious to the latter. So, we would probably be looking at crystaline life, if any. I think the problem with heavier metals would be polymerization. But you could argue that polymerization is not necessary as well, just like saying a lack of complex molecules with ring structures are not a problem with silicon. If we start throwing out ALL assumed pre-requisites for molecules involved in life anything is possible. We should be careful not to fall in the trap of personal incredulity, but I think carbon, hydrogen, nitrogen, oxygen, and phosphorous would be universal in the building of life. To me, silicon seems to have too much going against it, even without competition. It is a fun exercise in thought, however.

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Just for example, CO2 is a gas and SiO2 can be an amorphous liquid (glass) or a solid crystal (quartz). Just from this example, I would have to say no it can't replace carbon straightaway. Silicilic acid, which sounds hopefully like a liquid or at least water soluble is in fact neither. The closest carbon equivalent to silicilic acid is performic acid (CH2O3), which is readily water soluble. Silicon containing molecules seem quite different than their carbon analogues in almost every sense.

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Agreed, 100% - you can't just substitute silicone for carbon in chains.

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Silicon could, however, create long polymers like carbon. But as previous posts have stated, double bonds seem to be a problem as are ring structures. Nitrogen or phosphate, if anything, would seem to be a better bet than silicon in this respect.

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Can you name a single long, stable nitrogen or phosphate-based chain?Also, can you explain why double bonds and rings are necessary for life?

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Just looking through the Merck Index (old 8th edition, 1968) silicon dioxide can be dissolved in hydroflouric acid to produce silicon tetraflouride, a gas. It also says that glass can be "slowly attacked" by heating with concetrated phosphoric acid. The crystal form (quartz) seems impervious to the latter. So, we would probably be looking at crystaline life, if any.

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Many forms of silicone are soluable and are fluids - of course analyzing merely simple mineral forms are going to find you a lot of solids that don't dissolve well. You'd find the same thing if you attacked simple forms of carbon (graphite, diamond, etc).Silicones can take on an incredible diversity of forms, because just like a single-bond carbon chain, a silicone chain can have two R-groups per central monomer and three for each end - dramatically altering its own property if you have functional groups attached.

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Based on the periodic table (I'm not a chemist) (and that is the only reason we are discussing silicon) lead and tin may have a similar chemistry to carbon. Could a lead and tin sea on a planet like Mercury support a life chemistry?

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I think the problem with heavier metals would be polymerization. But you could argue that polymerization is not necessary as well, just like saying a lack of complex molecules with ring structures are not a problem with silicon. If we start throwing out ALL assumed pre-requisites for molecules involved in life anything is possible.

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However, without polymerization, you're not going to be able to have complex state information, and probably not complex catalysts. I fail to see what requirement of life is being met by "rings" and "double bonds". And, once again, silicon *can* double bond and form rings, just not as readily as carbon - you just probably can't get any benzene-style rings going, though.

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I'm inclined to think that life is such a surprising emergent property of the basic chemistry that we should be pretty careful about ruling it out. However, it is very clear we don't know enough to settle the question either way?

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I'd agree to that. It's idle speculation, but fun idle speculation.

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We should be careful not to fall in the trap of personal incredulity, but I think carbon, hydrogen, nitrogen, oxygen, and phosphorous would be universal in the building of life.

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I wouldn't For example, defend why you think phosphorus is necessary for life.Also, if you're going down the "LAWKI-only" route, you might as well add sodium... and potassium... (etc) ------------------
"Illuminant light,
illuminate me."[This message has been edited by Rei, 11-12-2003]

Just for your reading, here is an interesting article on the chemistry of silanols - which are commonly found in low concentrations all over earth. It's one again another example of how complex silicon-based chemistry can be.http://www.ch.ic.ac.uk/ectoc/ectoc-3/pub/010/------------------
"Illuminant light,
illuminate me."

Sorry, I guess I'm still confused.As DNA already mentioned, I also was under the impression that silicone (with an 'e') was a man-made substance.Silicon (no 'e') is the element and silicates are minerals containing Si and O.To me, it almost looks like you all are talking about silica (with an 'a' )- SiO2. Of which quartz (crystalline structure), agate (cryptocrystalline structure), and opal (amorphous; SiO2+H2O) are examples rather than silicone or silicon.As far as I know, there are no natural occurrences of pure silicon (Si), so I am confused by your saying "amorphous silicon" and "silicone is not just silicon and oxygen."Sorry if I'm not catching on and if you are having to repeat yourself. And thanks for your earlier response.[This message has been edited by roxrkool, 11-12-2003]

Silicon: The element. When pure, it can take two forms: amorphous, and crystalline. Crystalline has an orderly bonding pattern, and is not nearly as reactive as amorphous. Amorphous silicon can be made from SiO2 by heating in an oxygen-poor environment with a chemical that wants the oxygen more than the silicon (such as carbon).Silicates: Chemicals based on silicon. The most common natural form is SiO2 in a crystaline lattice, although this is anything but the only natural form. For example, check out my paper on silanols, which are common in nature also, and read about how, depending on the form, they can form sheets, chains, and perform all sorts of catalytic reactions.Silicone: A polyermization of silicon and oxygen, with alternating Si/O/Si/O... (etc) bonds. Each central monomer has two R groups, and the ends have three. Do you know what an R group is?There are many ways to make silicones (such as reacting silanes with an oxygen donor), and there is no reason why it has to only be made in the laboratory.Silanes: Silicates with most bonds filled with hydrogenThere are natural occurances of pure silicon - however, just like carbon, it tends not to last too long on earth in a completely pure state. Do you know what amorphous molecules are? Lastly, silicone is not just silicon and oxygen, because of the R groups.Did I miss anything?------------------
"Illuminant light,
illuminate me."

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Just looking through the Merck Index (old 8th edition, 1968) silicon dioxide can be dissolved in hydroflouric acid to produce silicon tetraflouride, a gas. It also says that glass can be "slowly attacked" by heating with concetrated phosphoric acid. The crystal form (quartz) seems impervious to the latter. So, we would probably be looking at crystaline life, if any.

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I don't think you have an argument there:
(a) HF (hydrofluoric acid) is an extremely strong acid. It will dissolve human skin, tissue, muscles (not bones IIRC). It will strongly wet glass ("crawl" out of beakers on its own), therefore you need plastic beakers and storage vessels.
(b) HF is (fortunately) not a very abundant compound.
(c) Your conclusion of "crystalline life" does not follow the premises. Many carbon containing compounds are soluble, many are not (graphite or diamond - both crystalline species of carbon) are not readily soluble.

Thanks for answering my questions. I have a few more.I think my problem stems from my minerals background where I use terms differently. You are a chemist???

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Rei:

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Silicon: The element. When pure, it can take two forms: amorphous, and crystalline. Crystalline has an orderly bonding pattern, and is not nearly as reactive as amorphous. Amorphous silicon can be made from SiO2 by heating in an oxygen-poor environment with a chemical that wants the oxygen more than the silicon (such as carbon).

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Okay, I think I am inderstanding what you are saying about silicon. You are basically referring to how elemental silicon can be separated from silica (SiO2) by smelting sand (or another form of silica) in the presence of carbon. And the resulting man-made elemental silicon takes an amorphous form.What then causes elemental silicon to take a crystalline form and from what or how is it derived?

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Silicates: Chemicals based on silicon. The most common natural form is SiO2 in a crystaline lattice, although this is anything but the only natural form. For example, check out my paper on silanols, which are common in nature also, and read about how, depending on the form, they can form sheets, chains, and perform all sorts of catalytic reactions.

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In my neck of the woods, silicates are minerals containing the SiO4 (-4 charge) tetrahedron so would not include SiO2 (silica) - I think that's one of the reasons I was getting confused. It sounds like silanols are similar in form to silicates.You don't use the term 'silica?'

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Silicone: A polyermization of silicon and oxygen, with alternating Si/O/Si/O... (etc) bonds. Each central monomer has two R groups, and the ends have three. Do you know what an R group is?

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I think I was initially confused because I have not seen any mention of silicone being a non-natural product. It does not occur in nature, does it? I understand that it is a polymer and that R groups are (I THINK!!) groups of [bonded?] chemical elements that do not change the properties(?) of the main molecule to which they are attached.

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There are many ways to make silicones (such as reacting silanes with an oxygen donor), and there is no reason why it has to only be made in the laboratory.

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Oh, so silicone IS found in nature? Or at least you see no reason why it should not. And I think I understand now that silicone is NOT only used as a lubricant, etc., but has other properties [and forms?] that make it an interesting product.

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Do you know what amorphous molecules are? Lastly, silicone is not just silicon and oxygen, because of the R groups.

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Well I know what amorphous minerals/structures are - irregular chains of molecules (i.e., no internal structure). As opposed to crystalline forms where molecules are arranged in an orderly fashion.

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Did I miss anything?

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Nope, I think I am beginning to understand now - am I? I am going to go back and re-read this thread now that I have a better understanding of the terminology you're using. Thanks again.[geekspeak]I'm off to a talk about the Earth's Interior - yahoo!!! [/geekspeak]

Just going by what the Merck Index says. But you are right, Flouride on its own is a VERY reactive substance. Triflouroacetic acid is probably the nastiest stuff I've worked with in the past few years. Trichloroacetic acid by comparison is much less reactive. Outside of a lab, HF is not that abundant and probably reacts with something as soon as its formed. What I was trying to show was that Silicon Dioxide, or silica, is very non-reactive except with very strong acids (perhaps the strongest acid). What I was trying to say is that if silicon dioxide was the basis for life it would be more crystaline in nature, or at least less pliable than the life we know here on Earth.As Rei pointed out in a previous post, silanols can dissolve in water (I think) so maybe this could be the base for genetic polymers, who knows.[This message has been edited by Loudmouth, 11-13-2003]

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I think my problem stems from my minerals background where I use terms differently. You are a chemist???

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No, but my partner majored in Chemistry and I find the topic really interesting, so we often discuss it I myself am still learning, so any input is greatly appreciated.

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Okay, I think I am inderstanding what you are saying about silicon. You are basically referring to how elemental silicon can be separated from silica (SiO2) by smelting sand (or another form of silica) in the presence of carbon. And the resulting man-made elemental silicon takes an amorphous form.

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Correct, although there's no reason it has to be man-made. Any heat source and compound that wants the oxygen more than the silicon will do.

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What then causes elemental silicon to take a crystalline form and from what or how is it derived?

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It's not easy, and it's not something you'd expect to find much in nature. Here's an article on the subject - they can make it from deposition from silanes (which can also produce amorphous silicon). Most of the research on this front is for computer chip manufacture. In nature, you'd expect to find notably more amorphous silicon.

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It sounds like silanols are similar in form to silicates.

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Silanols are compounds that contain one or more SiOH groups; the most basic form is silicic acid. Also, I apologize, I wasn't specific enough in my definition of silicates. Silicates are only the salts and esters of silicon; I was using it more generally than I should have.

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You don't use the term 'silica?'

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SiO2. It can be in a number of forms.

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I think I was initially confused because I have not seen any mention of silicone being a non-natural product. It does not occur in nature, does it?

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Certainly not in bulk; however, I've seen a number of reference to how silicon polymers do exist in nature, on Earth, but never any specifics. If you can find any specifics either to the affirmative or the negative, I would greatly appreciate it.

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I understand that it is a polymer and that R groups are (I THINK!!) groups of [bonded?] chemical elements that do not change the properties(?) of the main molecule to which they are attached.

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Not quite. R groups mean the same thing with silicon-based chemistry that they do with carbon based: "Stick Something Here". It can be a chlorine, a hydrogen, a phosphate, a carbonate, another silicon chain, a carbon chain - whatever you want that will bond. Depending on what you pick, you can radically alter the properties of the chain. For example, "Silly Putty" is a silicone in which all of the R groups are CH3.

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Oh, so silicone IS found in nature? Or at least you see no reason why it should not.

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Right. I've seen allusions to "silicon polymers" occuring in nature, but haven't found specifics. I see no reason why even on earth we wouldn't expect to find some silicon polymers, but earth has the additional hindrance of an oxygen-rich atmosphere. I've not run into a single silicon polymerization method which is conducted in an atmosphere that contains oxygen.

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And I think I understand now that silicone is NOT only used as a lubricant, etc., but has other properties [and forms?] that make it an interesting product.

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Yes. They can range in physical properties from liquids of varying fluidity, to plastics of all kinds, to molecules that form thin sheets, to resins that further polymerize when water is removed, to all sorts or rubberlike and elastic materials. I'm not aware of how much work has been done with the incorporation of metallic ions into silicone polymers, but metallic ions in other forms of silicon (replacing silicon molecules in a silica lattice), such as zeolites, are incredibly valuable for their shape-selective catalytic properties, and much more. There's currently a lot of research going on into making chiral zeolites, which would be incredibly useful in separating chiral compounds of drugs. If you can find any more information on this subject, I'd be greatly appreciative.I really think that, given how much humans have been able to achieve with silicon without having life-created compounds to start with, they actually have a shot at life on other, albeit rather different, planets. It's a rather interesting set of chemistry; the d-orbital allows for more complex chemistry than carbon in some manners, but it is up to the R groups to prevent, in the absence of double bonds, the polymer from rotating around any axis. The more I read about it, the more interested I am - for example, over the course of this discussion, I've ran into how cyclic silicon polymers (cyclic oligosiloxanes) do in fact form quite readily, which my opponent initially claimed doesn't happen.I, myself, am still just learning as well. ------------------
"Illuminant light,
illuminate me."(edit: whoops, sorry about the unclosed HREF!)[This message has been edited by Rei, 11-13-2003][This message has been edited by Rei, 11-13-2003]

Ack! Rei! Edit! Include a [/URL]!

That's one big honkin' link!!!Thanks again for your response. I'm going to go back now and try to understand things a bit better.

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2a) The atmosphere is considered by most scientists to have been neutral or weakly reduced when life appeared on Earth, and to have stayed that way for something like one billion years. So the hypothetical silicon-based life could have appeared 4 or so billion years ago and free oxygen in the atmosphere shouldn't have been a problem.

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Ah, so you expect multiple kinds of life forms to evolve at the same rate on the same planet.

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You do know the difference between abiogenesis and evolution, don’t you?

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And why, perchance, would you expect that?

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I wouldn’t...I don’t think silicon-based life is plausible.But, as I am sure you are well aware, arguments are often times formulated by accepting the opposing party’s position as true, for the sake of argument, and then seeing what one would expect. If it were true that life based on silicon was plausible, then I would suspect that many people would expect such life to arise on a planet where both silicon and oxygen were abundant and the atmosphere lacked molecular oxygen.

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2b) Molecular oxygen was a poisonous gas for the first carbon-based life forms too. But over the roughly billion years that the oxygen levels climbed, they evolved methods of dealing with the problem (and some even evolved methods of utilizing the oxygen).

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Again, you're assuming the same rate. Why on Earth would you assume that?

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Why on Earth would you assume that something like a billion years is insufficient time for your hypothetical silicon-based life to arise and evolve methods of dealing with supposed problems involving molecular oxygen?

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So if carbon-based life could have arisen and then surived despite increases in atmospheric oxygen, why couldn't putative silicon-based life?

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why on Earth as well would you expect the same planet to be equally suitable to multiple, highly different forms of life?

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Because of what you’ve said.Your hypothetical life form is based on silicon, which is the second most abundant element in the Earth’s crust. That isn’t suitable for supposed silicon-based life?Carbon-based life has little need for silicon, so there would be no direct competition between known life and your hypothetical life for the primary element of your putative life formthat isn’t suitable for silicon-based life?In fact, as you point out, the fact that the life forms would be highly different would suggest little competition for shared resources...that isn’t suitable for silicon-based life?Your hypothetical life form also has oxygen as a primary component: oxygen is THE most abundant element in the Earth’s crust. That isn’t suitable for supposed silicon-based life?And exactly where do you suggest IS suitable for silicon-based life?

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Ah, so you expect multiple kinds of life forms to evolve at the same rate on the same planet.

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You do know the difference between abiogenesis and evolution, dont you?

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Yes, I know - from your viewpoint, abiogenesis is a point event, right? It's certainly not the ToE, but virtually all conventional views of abiogenesis involve it occurring over time, involving various sorts of selective processes.

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And why, perchance, would you expect that?

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I wouldnt...I dont think silicon-based life is plausible.

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But, as I am sure you are well aware, arguments are often times formulated by accepting the opposing partys position as true, for the sake of argument, and then seeing what one would expect. If it were true that life based on silicon was plausible, then I would suspect that many people would expect such life to arise on a planet where both silicon and oxygen were abundant and the atmosphere lacked molecular oxygen.

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And you would expect the same temperature constraints, the same ratios of different elements, the same levels of geothermal activity, the same atmospheric pressure, same surface area covered in water (or other liquids), etc, to be ideal for each? What on earth would lead a person to such a conclusion? They have different chemistries, so they're going to have different optimal situations.

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Again, you're assuming the same rate. Why on Earth would you assume that?

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Why on Earth would you assume that something like a billion years is insufficient time for your hypothetical silicon-based life to arise and evolve methods of dealing with supposed problems involving molecular oxygen?

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It took a billion for carbon, so don't act like it's some sort of "easy, fast" period of time. I don't expect that the same planet would be equally compatable for carbon based life as with silicon; quit painting me into supposedly believing that.

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why on Earth as well would you expect the same planet to be equally suitable to multiple, highly different forms of life?

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Because of what youve said.

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Your hypothetical life form is based on silicon, which is the second most abundant element in the Earths crust. That isnt suitable for supposed silicon-based life?

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Ah. So if you had a ball of pure carbon sitting a few degrees above absolute zero with no geothermal activity, no water, an an atmosphere of sulphuric acid, would you expect life? How about a ball of pure carbon at 800K with intense tectonic activity and an atmosphere of H2 and He? (I could go on). The point is, the total concentration is probably one of the least relevant issues to whether life will occur.

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carbon-based life has little need for silicon, so there would be no direct competition between known life and your hypothetical life for the primary element of your putative life formthat isnt suitable for silicon-based life?

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1) Once again, I'll state it, hopefully for the last time. I see no reason at all why the same planet should be equally suitable for multiple different kinds of life; each would have their own optimal environments.2) If carbon based life established more quickly, and created an oxygen-rich atmosphere, it makes it all the harder for silicon-based life to establish.

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And exactly where do you suggest IS suitable for silicon-based life?

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Notice how you put "where", as if we've already detected a measurable percentage of solid planets in the universe. This goes back to your assumption that the miniscule percentage of the universe we've looked at is enough to tell that Earth has the only life on it, right?It would be a planet with ample "hot spots", with an oxygen-poor atmosphere, overall lower temperature, possibly a non-water solvent (I haven't looked into other solvents for silicon enough to know whether water or another solvent would be ideal - there are believed to be liquids on the surfaces of other bodies even in our solar system that aren't water, such as on Titan). Oxygen would be locked up in minerals, including around the hot spots, but there wouldn't be enough oxygen on the planet for everything that would preferentially bond with it. There would be a diversity of concentrations of different chemicals on the planet. Hmm... what else would make it ideal for silicon polymerization... I would ask you: How readily, had you been some sort of etheral entity with no knowledge of or connection to Earth, would you have been able to predict that a planet matching Earth's description would be ideal for carbon-based life?------------------
"Illuminant light,
illuminate me."

So your hypothetical silicon-based life, which would be unlike any life known, would exist on some hypothetical planet, unlike any planet known.To repeat a point I made at this forum a while ago; when putting forth arguments that rely upon "life as we don't know it", one leaves the empirically based and enters the realm of unsupported speculation. This goes double for those putting forth arguments that rely upon BOTH "life as we don't know it" AND "planets as we don't know them".Hey, I have no problem with people putting forth unsupported speculation (as I said, I have done so many times), as long as the one doing the speculating doesn't try to pretend that others must accept his/her position as correct.[This message has been edited by DNAunion, 11-15-2003]

Uh-huh. And the problem is, you enter the very same realm when you try to counter the argument.Yes, we're speculating. But so are you. Now that we're all on the same page, can we continue this very interesting speculation?