Prokaryotes stimulate mineral H_2 formation for the deep biosphere and subsequent thermogenic activity

摘要

The deep subseafloor biosphere contains two-thirds of Earth's prokaryotic biomass, which may indicate the presence of novel mechanisms of energy generation as temperatures increase in the subsurface. In sediment slurry experiments (0-100 °C) with a range of common minerals and rocks (including basalt and quartz), there is significant H_2 formation at elevated temperatures, but only in the presence of prokaryotes. This stimulates further prokaryotic activity, typical of deep sediments (sulfate reduction, acetogenesis, and CO_2 production, plus continuing methanogenesis), and Bacteria and Archaea representative of many deep sediment types develop. H_2 and acetate formation is particularly stimulated above 70 °C. This prokaryotic activity even enhances reactions when temperatures are raised to thermogenic levels (~125-155 °C), including hydrocarbon generation. Mechanochemistry may be important for mineral H_2 formation; this is enhanced by prokaryotes (biomechanochemistry), and subsurface stress and fracturing, which is widespread on Earth.