New Microbe Discovery: Tiny microbes discovered deep in the earth give scientists new clues on how they might search for life on Mars and answer the question: Did life on Earth begin underground?

Newly discovered microbes were found nearly two miles deep in ancient water seeping through a fracture in a 2.7-million-year-old rock formation. The rock contains radioactive uranium, thorium and potassium, as well as an iron-sulfur compound called pyrite, or fool's gold, among other constituents. A cascade of reactions supplies the microbes with their remarkable if meager diet. First, radioactivity cracks water molecules (H2O) into their components: hydrogen (H2) and oxygen (O). The detached oxygen atoms combine with adjacent water molecules to make hydrogen peroxide (H2O2). The peroxide then reacts with an iron-sulfur compound called pyrite (FeS2), producing sulfate ions (SO42-) that the microbes can "eat." Each sulfate ion is lacking two electrons, which are supplied inside the organisms by the conveniently available leftover hydrogen gas (H2). The microbes use that reaction to store energy.

For more information, visit the National Science Foundation's X-treme Microbes special report.