Rock-crushing derived hydrogen directly supports a methanogenic community: significance for the deep biosphere

Microbial populations exist to great depths on Earth, but with apparently insufficient energy supply. Earthquake rock fracturing produces H₂ from mechanochemical water splitting, however, microbial utilization of this widespread potential energy source has not been directly demonstrated. Here, we show experimentally that mechanochemically generated H₂ from granite can be directly, long-term, utilized by a CH₄ producing microbial community. This is consistent with CH₄ formation in subsurface rock fracturing in the environment. Our results not only support water splitting H₂ generation as a potential deep biosphere energy source, but as an oxidant must also be produced, they suggest that there is also a respiratory oxidant supply in the subsurface which is independent of photosynthesis. This may explain the widespread distribution of facultative aerobes in subsurface environments. A range of common rocks were shown to produce mechanochemical H₂ , and hence, this process should be widespread in the subsurface, with the potential for considerable mineral fuelled CH₄ production.