Is carbon preferable to silicon for life? If a planet would be very rich in silicon and only have traces of carbon, all other things being the same as on earth, would life evolve? Would it be as successful and efficient as on earth? What would the differences be?
Is carbon preferable to silicon for life?
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The earth is rich in silicon n but we have oxygen and oxygen and silicon have very strong bonds. I suppose it all depends what is the temperature if the environment. Life depends on many other compounds then carbon and oxygen , so if you make a substitution silicon for carbon , I think we will be out of luck
Could silicon be the basis for alien life forms, just as carbon is on Earth? (Ask the Experts - Space, Scientific American)
. . . . must be so . . . if conditions were more favorable for silicon-based life . . . I guess we'd have it preferentially over carbon.
(Tongue-in-cheek humor-->) I guess That's why I became a geologist . . . . I found myself walking around . . . head down most of my life . . . and lo and behold I began observing sand grains and rocks . . . my interest was thus tweaked and as a geologist, silicon became one of my favorite materials . . . I also favor silicon solar cells . . . and properly-placed silicon rubber inserts!
You were doing fine until the third word from the last - that's silicone.
So the short answer is that respiration in a Si-based critter produces silica, a solid. Valence alone is not the linchpin.
Yes carbon is preferable to silicon. Like carbon, silicon has 4 valence electrons in its outer shell which are important for chemical reactions, so on the surface it looks like a viable alternative. But there is also electronegativity, the measure of the atom to attract electrons, which is also a determinant of its chemical reaction properties. Carbon has an electronegativity of 2.55 while silicon is 1.9, a sizable difference. What this ultimately means for bio molecules is that they'll be less stable as they cannot attract the other atom's electrons as well, which is the bases of covalent bonding used in many bio molecules.
Another thing to consider is chirality/enantiomers, or handedness. If you're unfamiliar with it, it is when two molecules with the same number and type of atoms are arranged slightly differently so that they are mirror images of each other, a specific type of isomer. Sort of like how your left and right hand are slightly different. Carbon molecules often form with chirality, while few silicon molecules do. What chirality gives organisms is a much larger range of chemical reactions available through an increase in possible substrate structures, or the parts of the molecule that are responsible for starting chemical reactions, so more complex organisms.
With silicon life you're looking at weaker, unstable structures at the molecular level with much less variability. It is unlikely that silicon is the basis for life beyond the most simple lifeforms, carbon is much better and much more abundant.
Carbon builds a good number of strong bonds with many other chemicals, think carbon fibre, cellulose, fats, oils and a host of useful organic chemicals. It will react with metals and non-metals and many of these compounds are benign to living things too. If you were gonna choose a chemical to use for creating life, you could hardly choose better than carbon.
Yes. Enzymes catalyze reactions by having a specific structure as their active site, where the substrate(s)/reactants bind to the active site and then are catalyzed into whatever products the enzyme specifies. There are also things like cofactors that can change the structure of enzymes that the body uses to turn specific reactions on and off. Other proteins use active sites to transport molecules and atoms across the cell membrane and structures within the cell, a very important feature. A lot of this is determined by the geometric structure of the enzyme (which is why denaturation is so bad), which is derived by the way various molecules that make up the enzyme interact, and different base atoms in a molecule like carbon vs. silicon can yield different structures.
What chirality offers is a much wider range of geometric possibilities that allows things like enzymes to be more substrate/reactant specific, so more specific reactions are possible - (I'm making up numbers here) so instead of 2 or 3 possible reactions you now have a dozen. All else being equal, I don't think chirality absent molecules makes it harder for reactions to happen, but it can severely limit the number of possible reactions as in the case of carbon vs. silicon. And that is a limiting factor on what type of life is possible.
Since silicon compared to carbon makes unstable structures, and silicon is not known to produce long chains of hundreds of atoms like carbon, that is a further impediment on the structures silicon-based molecules can produce.
. . . and DIAMONDS!!!
I'm not saying they don't exist, only that silicon isn't known to have long chains of hundreds of silicon atoms in contrast to carbon, which is important for complex life. I'm not sure if the largest silicon molecules found in nature even reaches a dozen silicon atoms.
Not necessarily, never looked into SiO2 specifically compared to CO2, but that's besides the point (my guess is that the oxygen isn't as strongly bonded to silicon as carbon given that carbon has a higher electronegativity than silicon).
Biological molecules form biological structures composed of many molecules, and the analogous structures of silicon compared to carbon are less stable. That is what I'm saying. So a group of carbon based molecules in a ring structure is more stable than a group of silicon based molecules in a ring structure. And stuff like that is very important for the development of life.