In their search for environments that might mimic extraterrestrial ones, scientists have tended to go deep. Traditional sites for such exploration have been hydrothermal vents at mid-ocean ridges, populated by microbes that love methane and high temperatures. Researchers recently reported the discovery of such methanogens thriving in the depths of gold mines in South Africa, several miles deep in Earth's crust. Ice cores from Antarctic lakes have even uncovered dormant photosynthesizing cyanobac...