… researchers have long speculated that alien life could have a completely different chemical basis than life on Earth. For example, instead of relying on water as the solvent in which biological molecules operate, perhaps aliens might depend on ammonia or methane. And instead of relying on carbon to create the molecules of life, perhaps aliens could use silicon.
Carbon and silicon are chemically very similar in that silicon atoms can also each form bonds with up to four other atoms simultaneously. Moreover, silicon is one of the most common elements in the universe. For example, silicon makes up almost 30 percent of the mass of the Earth’s crust, and is roughly 150 times more abundant than carbon in the Earth’s crust.
Scientists have long known that life on Earth is capable of chemically manipulating silicon. For instance, microscopic particles of silicon dioxide called phytoliths can be found in grasses and other plants, and photosynthetic algae known as diatoms incorporate silicon dioxide into their skeletons. However, there are no known natural instances of life on Earth combining silicon and carbon together into molecules.