Glimpses of the Deep Biosphere

It may be that we shall find a simple general rule to apply: that microbial life exists in all the locations where microbes can survive, that would mean all the locations that have a chemical energy supply and that are at a temperature below the maximum one to which microbes can adapt. There would be no locations on the Earth that have been protected from “infection” for the long periods of geologic time.—Thomas Gold, The Deep Hot Biosphere, 1992If you’re reading this on one of our several fine continents, then the ground beneath your feet for four kilometers or more is full of fractured rock home to a starving, sleeping population of microbes. If you’re on an island or on the Pacific rim, then somewhere below you is a layer cake of microscopic wildlife that has accumulated over millions of years, and in the coolest parts of the crust (subducting tectonic plate edges) may extend down a dozen kilometers or more.These microbes at these great depths are demonstrably alive, but is this…