Silicon/Silicone based life

quote:

---

Finally, you have yet to address my question as to why we have no evidence whatsoever of silicon-based life here on Earth.

---

quote:

---

And you have yet to explain why you'd expect to find multiple types of life competing with each other...

---

quote:

---

And you have yet to explain why two fundamentally distinct life forms one based on carbon and the other (hypothetical one) based on silicon would be in any kind of direct competition with each other that would drive one to extinction.

---

Does the fact that carbon-based life has created a reductive atmosphere mean anything to you, as just a single example?------------------
"Illuminant light,
illuminate me."

quote:

---

Oh, don't you just love that last part! This author agrees that absence of evidence is evidence of absence!!! :-)

---

How many times does it have to be pointed out to you that finding random people who assert absence is evidence without looking at a measurable percentage of the whole is irrelevant, without a statistical base to show that most scientists believe it? Anecdotal cases are utterly irrelevant, and I wish you would stop asserting them. I can find random people if you would like who assert that the world is flat. Does that make the world flat?Let's do a quick search, just to get a rough idea of what people on the net as a whole are asserting:Not Evidence: 5540
http://www.google.com/search 1Evidence: 359
http://www.google.com/search 2And yes, there can be plenty of valid complaints to the validity of *those* numbers - but its far better than your selective picking of cases.Responding to this individual person's viewpoints:

quote:

---

Conceivably, some strange life-forms might be built from silicone-like substances were it not for an apparently fatal flaw in silicon's biological credentials. This is its powerful affinity for oxygen. When carbon is oxidized during the respiratory process of a terrestrial organism (see respiration), it becomes the gas carbon dioxide-a waste material that is easy for a creature to remove from its body. The oxidation of silicon, however, yields a solid because, immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens. Disposing of such a substance would pose a major respiratory challenge.

---

Carbon also has a strong affinity for oxygen (CO2 takes plenty of energy to split - in fact, if you heat silica and coke, you end up with CO2), but that hasn't stopped carbon-based life. Amorphous silica (SiO2) - which is what raw combustion of silicon produces, for the most part - is soluable in a number of substances (that's what most fluid silicon-based products are made from), including water. We know that hydrated amorphous silica occurs in nature even on Earth; opal is the natural slow deposition of it.This person's statement, "The oxidation of silicon, however, yields a solid because, immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens", is patently false. Yes, if you have steady deposition of SiO2, you can a crystaline silicone lattice, but that is just one of many possible outcomes."

quote:

---

The absence of silicon-based biology, or even silicon-based prebiotic chemicals, is also suggested by astronomical evidence. Wherever astronomers have looked - in meteorites, in comets, in the atmospheres of the giant planets, in the interstellar medium, and in the outer layers of cool stars-they have found molecules of oxidized silicon (silicon dioxide and silicates) but no substances such as silanes or silicones which might be the precursors of a silicon biochemistry.

---

While I've already covered this, I'll harp on it further: why would one expect to find any sort of life "in meteorites, in comets, in the atmospheres of the giant planets, in the interstellar medium, and in the outer layers of cool stars"? We've done only slightly better with carbon, finding only some basic amino acids in asteroids and comets. What percentage of the universe have we looked at? How many other sources of carbon-based life have we found? How on earth can we feel even the slightest bit justified using an "absence of evidence" argument with such a miniscule sample size?------------------
"Illuminant light,
illuminate me."{Shortened display forms of URLs, to restore page width to normal - Adminnemooseus}[This message has been edited by Adminnemooseus, 11-11-2003]

What she has presented is intermediate between the two ludicrous extremes that you have proposed.Review her messages, read for comprehension, and address what she did post rather than your favourite strawman.

quote:

---

Finally, you have yet to address my question as to why we have no evidence whatsoever of silicon-based life here on Earth.

---

quote:

---

And you have yet to explain why you'd expect to find multiple types of life competing with each other...

---

quote:

---

And you have yet to explain why two fundamentally distinct life forms one based on carbon and the other (hypothetical one) based on silicon would be in any kind of direct competition with each other that would drive one to extinction.

---

quote:

---

Does the fact that carbon-based life has created a reductive atmosphere mean anything to you, as just a single example?

---

1) I guess that could be considered competition, somehow, in some very weak sense. However, biological competition typically implies competition between two or more organisms for a shared resource; not the killing of one organism indirectly by a by-product of another.2) I assume when you say a "reductive atmosphere" you mean an oxidized one, as in, "Does the fact that carbon-based life has created [an oxidized] atmosphere mean anything to you, as just a single example?" Under that assumption I ask....so what?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.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).So if carbon-based life could have arisen and then surived despite increases in atmospheric oxygen, why couldn't putative silicon-based life?[This message has been edited by DNAunion, 11-09-2003]

quote:

---

1) I guess that could be considered competition, somehow, in some very weak sense. However, biological competition typically implies competition between two or more organisms for a shared resource; not the killing of one organism indirectly by a by-product of another.

---

The actions of one are killing another. That's competition.

quote:

---

2) I assume when you say a "reductive atmosphere" you mean an oxidized one, as in, "Does the fact that carbon-based life has created [an oxidized] atmosphere mean anything to you, as just a single example?" Under that assumption I ask....so what?

---

A reductive atmosphere is one filled with a reducing agent; in our case, oxygen. Any atmosphere filled with such gasses is reductive, be they oxygen, fluorine, or even xenon hexafluoride (ok, that would be a pretty bizarre world ). Oxygen is the most common example, because it's what we're most familiar with. Reductive atmospheres are a natural anomaly, because the reducing agent tends to get locked up in the rocks. You can get incredibly slightly oxygenated atmospheres from collisions of the solar wind with the surface of icy planets, for example, but to get an atmosphere with as much of a corrosive gas as ours essentially requires life. This is why scientists are trying so hard to be able to find and be able to directly image extrasolar planets; finding such gasses in the atmosphere (especially oxygen) in sizable quantities is a good indication that there is life on it.

quote:

---

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.

---

Ah, so you expect multiple kinds of life forms to evolve at the same rate on the same planet. And why, perchance, would you expect that?

quote:

---

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).

---

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

quote:

---

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

---

Even ignoring the rate issues, why on Earth as well would you expect the same planet to be equally suitable to multiple, highly different forms of life?------------------
"Illuminant light,
illuminate me."

Rei,
I'm pretty sure that oxygen doesn't qualify as a reductive agent. Oxygen itself is reduced in most reactions.. Classical examples of reductive agents would be hydrogen etc.
(Electron donors are reducing agents and would be found in the first few groups of the periodic table, electron acceptors, such as oxygen, are oxidative agents)
regards,
Alex

My apologies, Alex - just checked, and you are correct. I accidentally used the terms oxidatation and reduction backwards. The early atmosphere was a reductive atmosphere, and what we have now is an oxidizing atmosphere; the search is for the latter.------------------
"Illuminant light,
illuminate me."

Hmmm... I'm confused. I was under the impression that silicone was a lubricant, plastic, etc. Am I simply unaware of a new definition of silicone?

Silicone has many forms and uses, depending on its internal structure. It becomes even more varied in properties as you replace the silicon with various metal ions.Silicone is polymeric chains of alternating Si/O; in 3d, this typically means 2 oxygens per silicon. Random, irregular chains (amorphous) are easily produced by oxidation of SiO2. A lattice of SiO2 is hard and crystalline; one form is quartz.Silanes are hydrogenated silicon compounds. The hydrogens are easily stripped in the right environment (such as the presence of oxygen), making it an easily reactable compound.Zeolites are silicates which have a sizable quantity of the silicon replaced with various metal ions, creating ion channels that make them very useful as catylists and filters.Hmm... anything more I should define?------------------
"Illuminant light,
illuminate me."

quote:

---

Rei, I'm pretty sure that oxygen doesn't qualify as a reductive agent. Oxygen itself is reduced in most reactions.. Classical examples of reductive agents would be hydrogen etc.
(Electron donors are reducing agents and would be found in the first few groups of the periodic table, electron acceptors, such as oxygen, are oxidative agents)

---

Trying to avoid criss-crossing terms is why I try to use the terms REDUCED or OXIDIZED myself. It is less error prone to talk about the state of the compounds (for example, in the atmosphere) themselves rather than adding an additional mental step of electron/hydrogen transfers that can reverse the root terms and potentially lead to use of the wrong term. For example, methane by itself is reduced. That's pretty straightforward. But when involved in a redox reaction, methane is a reducing agent because it gets oxidized.[This message has been edited by DNAunion, 11-12-2003]

quote:

---

Hmm... anything more I should define?

---

I have a question. Silicone is made by people for use in many products; is it also a natural product?

It's an element.[This message has been edited by AdminNosy, 11-12-2003]

Someone tell me if I'm wrong, but are any of the silicone/silane derivatives water soluble? The nice thing about carbon based molecules is there ability to be hydrophylic and hydrophobic and these properties are used to life's advantage. It's hard for me to imagine life in solid state without depending on water soluble moeties. At best, silanes could be used for storing genetic information, but enzymatic activity and coenzymes with enough specificity and differentiation seem much less likely.Could it happen? Maybe, but I think it the extent of silicon based life might resemble hypercycles seen in proto-life here on Earth. I wouldn't expect anything approaching multicellular life, or even what we would term unicellular life. I could see self-replicating chemical reactions resembling surface catalyst reactions seen in catalytic converters for example, but I wouldn't be comfortable hypothesising beyond that.

I think the real issue isn't how well silicon chemistry fits in place of carbon. It is "Is there an environment where some element (maybe silicon) can support a chemistry complex enough to support the processes needed for life?"Is there something which silicon compounds can disolve in?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?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?

quote:

---

I have a question. Silicone is made by people for use in many products; is it also a natural product?

---

I'm not sure how long of chains we find occurring on earth, I've never looked into it - it's commercially easier anyway to just make some because the process is so simple. The big problem with earth is an oxygen-rich atmosphere. As I mentioned earlier, amorphous silicon (which is easily polymerized, unlike crystaline silicon) can be produced simply by heating SiO2 in an environment with a chemical that has a stronger affinity for oxygen; for example, if you heat SiO2 in the presence of coke (a heavily bonded form of carbon) in an oxygen-poor atmosphere, the carbon will capture the oxygens from the silicon. In fact, that's exactly how we produce silicon - we heat quartz sand with coke. In an oxygen-poor but energy rich planet, one would expect reactions such as this quite often. On earth, an oxygen-rich atmosphere decreases the odds of such a thing - just like an oxygen-rich atmosphere would have made it harder for early carbon-based organic compounds to form. There are several ways the amorphous silicon can then polymerize; it can form into an acid (such as silicilic acid) and then react with a variety of substances; it can form silanes in the presence of a hydrogen donor (which later, when encountering an oxygen donor can polymerize; you just don't want too fast of a reaction, or it will crystalize); etc. I'd have to read up more to get you specifics, however, it's been a while since I looked into this.Also worthy of note is that often silicone is not just silicon and oxygen; in fact, every monomer can have two R groups attached, which need not be silicon or oxygen.------------------
"Illuminant light,
illuminate me."