The deep, hot biosphere.

TLDR

Microbial life is likely widespread in Earth's deep crust and possibly on other planetary bodies, as evidenced by ocean vent communities and subsurface conditions that could support life even on inhospitable surfaces. Deep subsurface microbes derive energy from chemical sources supplied by upward‑moving fluids, independent of solar energy or surface conditions. The deep biosphere could rival surface life in biomass and may explain biological molecules in outer crust materials, challenging the assumption that such molecules originate solely from surface deposits.

Abstract

There are strong indications that microbial life is widespread at depth in the crust of the Earth, just as such life has been identified in numerous ocean vents. This life is not dependent on solar energy and photosynthesis for its primary energy supply, and it is essentially independent of the surface circumstances. Its energy supply comes from chemical sources, due to fluids that migrate upward from deeper levels in the Earth. In mass and volume it may be comparable with all surface life. Such microbial life may account for the presence of biological molecules in all carbonaceous materials in the outer crust, and the inference that these materials must have derived from biological deposits accumulated at the surface is therefore not necessarily valid. Subsurface life may be widespread among the planetary bodies of our solar system, since many of them have equally suitable conditions below, while having totally inhospitable surfaces. One may even speculate that such life may be widely disseminated in the universe, since planetary type bodies with similar subsurface conditions may be common as solitary objects in space, as well as in other solar-type systems.