Which microbes thrive below us in darkness -- in gold mines, in aquifers, in deep boreholes in the seafloor -- and how do they compare to the microbiomes that envelop the Earth's surfaces, on land and sea? The first global study to embrace this huge question reveals astonishingly high microbial diversity in some subsurface environments, pointing to vast, untapped, subsurface reservoirs of diversity for bioprospecting new compounds and medicinals, for understanding how cells adapt to extremely low-energy environments, and for illuminating the search for extraterrestrial life.
