Let’s start with abundance. Carbon is ten times more abundant than silicon in our solar system. This isn’t to say that silicon isn’t abundant—in fact, there’s more of it in Earth’s crust than there is carbon. And that’s part of the problem. Silicon, while more abundant in the crust, is less accessible than carbon, because it’s tied up in the form of silicates and other rocky materials. What’s more, because carbon is the winner in cosmic abundance, it’s more available to cosmic processes, many of which are now known to create prebiotic molecules. In the clouds of gas and dust between the stars, many organic compounds are formed, including cyanide, carbon monoxide, and even amino acids and benzenes. Of the 75 or so molecules found in interstellar space, only ten are made with silicon.