NARRATOR: Just because a planet can support life, does that mean it will? Here on Earth, the chemistry of life relies heavily on the element carbon. Carbon is one of the most versatile elements. Each carbon atom can hook up with one, two or three or four other atoms. It can even link up with other carbon atoms, creating long chains or rings. Throw in a few other elements and you've got amino acids-- the ingredients of proteins, the building blocks of life as we know it.

JACK COHEN: Carbon is a very useful element to sit at the center of life's chemistry. There's a lot of it in the universe. It's made very easily in stars. It makes very complicated meshed-together compounds, which have the possibility of changing each other's properties. You can have a really complicated, complex setup with carbon. I'd expect that very nearly all life forms we come across that are matter-based are going to be carbon-based.

NARRATOR: If carbon helps make life happen then there might be a lot of life out there. Carbon is one of the most common elements in the universe. Accessibility provided by the U.S. Department of Education.