Long Summary
Deep underground, far from sunlight, microbes sustain life through energy generated when rocks crack. A recent study identifies hydrogen gas and oxidants produced during fault movements as the key sources of this energy, challenging the long-held belief that all life depends on sunlight. Researchers from the Guangzhou Institute of Geochemistry in China mimicked earthquake conditions in high-pressure lab experiments to understand this phenomenon.
The experiments revealed that free radicals generated from rock fracturing split water molecules, resulting in the production of hydrogen gas and hydrogen peroxide. This hydrogen production triggered by fault slip was found to be up to 100,000 times greater than other known hydrogen-producing pathways, suggesting a significant energy source for subsurface microbial life.
While sunlight only penetrates a few yards beneath the Earth's surface, the deep biosphere below hosts around 15 percent of Earth's biomass, mostly bacteria and archaea. The continual fracturing of silicate-rich crustal rocks due to plate tectonics and frequent microquakes creates reactive radicals that generate hydrogen and peroxide, providing vital chemical energy to these underground microbial communities.
Laboratory fault experiments showed hydrogen production rates that greatly exceed natural processes like serpentinization and radiolysis. Such hydrogen bursts offer millions of times more energy than a single microbe requires for survival, effectively turning fresh rock cracks into temporary but vital oases. Field observations, including hydrogen spikes before earthquakes and presence of oxygen from peroxide breakdown, support these laboratory findings.
However, hydrogen alone is insufficient; microbes also need electron acceptors. The study demonstrated how hydrogen atoms convert ferric iron to ferrous iron and vice versa via hydrogen peroxide, creating a self-sustaining iron redox cycle. Some bacteria harvest energy by cycling iron in rocks, producing rust and supporting carbon cycling underground. This redox interface can persist for years, potentially expanding habitats for subsurface life worldwide.
These findings not only reshape our understanding of Earth's deep biosphere but also provide insights for astrobiology. Rocky planets like Mars, Europa, and Enceladus, with fractured crusts and iron chemistry, may harbor similar habitable environments beneath their surfaces. Detecting hydrogen, methane, or iron transitions on these worlds could guide future searches for extraterrestrial life, narrowing the hunt to rock cracks where chemistry and biology intersect.
