Carbon works here, and more specifically our form of carbon-based life works here, because of the proportion and availability of other elements. Change that ratio (e.g. by limiting available nitrogen) and something else might become more ideal for the basic information storage and catalytic functions necessary. Once again this is specific to our environment.
I strongly disagree for three major reasons:
1) The 'specific to our environment' argument is nonsense given that 'our environment' has changed significantly. The 'primordial soup' is a very significantly different environment to what we have now. The very early Earth would've been molten rock bathed in hydrogen and helium. As the crust cooled, volcanism resulted in the spewing of large amounts of amonia (and hence nitrogen) and carbon dioxide into the atmosphere. Photochemical decay of the amonia resulted in free nitrogen. Don't ask me how the archae came around, but they did. These things ate sulphur. Then after a long period of time, we get photosynthesis. Photosynethic activity then liberated oxygen and sequestered carbon. Biochemistry has a direct impact on environment, just as environment determines biochemistry.
2) Carbon is simply more 'interesting'. Yes, Silicon can
form interesting molecules that could carry biologicaly significant information. But Carbon can react to form 'interesting' combinations with a faaar wider range of atoms. To quote an intresting PNAS paper
As the structural basis for life, one of carbonís important features is that unlike silicon it can readily engage in the formation of chemical bonds with many other atoms, thereby allowing for the chemical versatility required to conduct the reactions of biological metabolism and propagation. The various organic functional groups, composed of hydrogen, oxygen, nitrogen, phosphorus, sulfur, and a host of metals, such as iron, magnesium, and zinc, provide the enormous diversity of chemical reactions necessarily atalyzed by a living organism. Silicon, in contrast, interacts with only a few other atoms, and the large silicon molecules are monotonous compared with the combinatorial universe of organic macromolecules
Any idea or suggestion that silicon could
be the basis of biochemistry is a non-scientific claim, based on personal preference, that disregards every single bit of evidence we have about life, biochemistry, and chemistry. Be it deep sea thermophiles or cryptoendolithic cyanobacteria in antarctica
, life irrespective of its environment, is carbon based. This could be because Carbon makes for a real good way of transfering energy (double and triple bonds, which is something that silicon can't do).
The available evidence we have suggests that irrespective of drastically different environments, different metabolic pathways (e.g. sulphur-metabolising bacteria
), we end up with carbon at the core of the system.
Yes, I'm aware that the argument that truly alien biology could be based on something else but it would be so alien that we wouldn't recognise it as being alive. We'd probably regard it as a rock, and they'd probably not actually see us as we'd be moving too quickly.
3) Astronomically speaking, carbon is massively more abundant than silicon, phosphorus-nitrogen (for phosphazene-based biology), and so on.
And here is the fun thing, it is not just specific to our environment now it is specific to the particular path both life and the planet have developed on since the moment of life's advent. This is an extremely path-dependent process
That's not necessarily true. This goes back to the Burgess Shale interpretation. Gould would argue that anything is possible (see "Life's Grandeur"), but Conway Morris (see "Lifeís Solution: Inevitable Humans in a Lonely Universe")would argue that there are systemic constraints on how we could have developed. Gould says that we could have ended up as anything, but Conway Morris says that we could only ever have been human or something like it. I don't know which way I go. Unfortunately, we can really easily falsify either proposition.
... something about the Drake equation...
There is no correct way to caluclate the possibility of alien life. The Drake method is just one way of writing down a long list of imponderable variables.