There is an entire ecosystem that thrives in dark corners of the ocean, miles below the surface.  Huddled around deep-sea hydrothermal vents, the bacteria, tubeworms, clams, and other animals that live here get their energy not from the sun, but from chemicals like hydrogen sulfide. Humans, and almost every other land and sea animal on this planet, inherit energy originally from the sun. If all of Earth’s animals do not receive energy from the same source, what does unite them? What do astronomers need to find on another planet before searching for life there?

Recorded June 2010; Posted September 2010