Silicon-Based Life

All known life on earth uses Carbon as its base, because it is plentiful and can bond with four other atoms. Silicon, in the same column on the periodic table, has been speculated to be the base of some alien life.

Unfortunately, because silicon cannot form double bonds like carbon, silicon-based structures would be too fragile to create large molecules. Additionally, while carbon dioxide is a gas, silicon dioxide is a solid, making it difficult to expel.