this post was submitted on 24 Sep 2023
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I've always wondered why we should assume that life that evolved separately from us for some reason had to be carbon based. We know (as far as I know) next to nothing about how life arises from non-living chemicals, so as far as I can tell, there's no reason to believe that carbon based life is more common than other life forms (except for the fact that 100% of observed life is carbon based of course).
There's good reason to presume carbon is required. Carbon has some nice, and totally unique properties that allow it to facilitate life.
The most important features to carbon in this context are:
Stable catenation of atoms. Carbon atoms can bond to other carbon atoms in a long chain, and that chain does not become appreciably more reactive. This allows for the construction of very large molecules with specialized mechanical functions.
Ability to form stable multiple bonds. Carbon can form single, double, or triple bonds with itself (and oxygen and nitrogen), which allows carbon-based molecules to have ridgid shapes. Double bonds are found all over the place in life because they allow molecules to have sections that aren't just wiggly noodles of atoms.
Bond stabilities that fall in a kind of "goldilocks zone" where carbon bonds to other atoms are strong enough to resist falling apart, but weak enough to be broken later.
Nearly identical electronegativity to hydrogen. Carbon pulls on the electrons in its bonds about the same amount as hydrogen. This allows it to make stable bonds that are non-polar, which, when used in conjuction with other, more electronegative atoms (particularly oxygen and phosphorus) allow Carbon-containing molecules to be hydrophobic, hydrophilic, or both simultaneously. This property is what allows for complex structures like Lipid bilayers and proteins to be formed.
No other atom, not even silicon, has this set of properties, and it's very hard to imagine how you would make all but the most simplistic verson of life without these.
Oh wow, carbon is why our cells are a thing
It's been a long time since I took a biology course, but I think the reason why we believe carbon-based life is more likely is because carbon is far more likely to bond with other elements to form the complex structures nessecary for life at a molecular scale. The only other element that comes close is silicon and it's no where near as good as carbon.
I think it has something to do with the number of electrons in it's outer shell, and how reactive the chemical is. A biochemist could tell you more than me.
There's also silicon.