Tectonically-driven oxidant production in the hot biosphere

Genomic reconstructions of the common ancestor to all life have identified genes involved in H 2 O 2 and O 2 cycling. Commonly dismissed as an artefact of lateral gene transfer after oxygenic photosynthesis evolved, an alternative is a geological source of H 2 O 2 and O 2 on the early Earth. Here, we show that under oxygen-free conditions high concentrations of H 2 O 2 can be released from defects on crushed silicate rocks when water is added and heated to temperatures close to boiling point, but little is released at temperatures <80 °C. This temperature window overlaps the growth ranges of evolutionary ancient heat-loving and oxygen-respiring Bacteria and Archaea near the root of the Universal Tree of Life. We propose that the thermal activation of mineral surface defects during geological fault movements and associated stresses in the Earth’s crust was a source of oxidants that helped drive the (bio)geochemistry of hot fractures where life first evolved.