6. Why Carbon?

Recently a scientist friend of mine read a story I’d written about the exploration of Europa’s biosphere. He liked the story, but he thought he’d found a huge scientific flaw. He was dismayed that I’d based my Europan lifeforms on carbon—worse, that I’d built them with amino acids, phospholipids and other molecules found in Earthly organisms. Wouldn’t alien creatures have a completely, well, alien biochemistry? Wouldn’t they most likely be based on a different chemistry altogether, eschewing carbon for some other element with similar chemical properties?

Possibly. But not probably. Now, it’s not unreasonable to speculate about such things. Remember the periodic law—elements in a particular column of the table will have similar chemical properties. If you refer to the table, you’ll see that silicon, Si, lives right under carbon. Silicon, like carbon, can form chains and lattices, and it binds to the same family of elements as carbon does. And silicon, as we’ve already seen, is one of the ten most abundant elements in the universe. So why not base life on silicon, instead of carbon?