I imagine CO2 as a kind of a Lego brick. It can be plucked from the air and added one carbon at a time on to other molecules. Silicon oxides in contrast … well, you try building with sand. Silicon or other elements might be amenable to use by a higher intelligence such as ourselves, but it is hard to see how life could have bootstrapped itself from the bottom up using silicon. That’s not to say that silicon-based life couldn’t possibly evolve in an infinite universe, who could say; but as a matter of probability and predictability, which is what this book is about, that seems overwhelmingly
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