Serpentinization and the inorganic synthesis of H2 in planetary surfaces

The near-surface inorganic synthesis of molecular hydrogen (H2) is a fundamental process relevant to the origins and to the sustenance of early life on Earth and potentially other planets. Hydrogen production through the decomposition of water is thought to be a principal reaction that occurs during hydrothermal alteration of olivine, an iron–magnesium silicate abundant near planetary surfaces. We demonstrate that copious amounts of H2 are produced only when the olivine undergoing alteration (serpentinization) contains 1 to 50 mol% iron over a variety of planetary surface P–T conditions. This suggests that extrasolar Earth-like planets that are hosted by a star with iron contents up to two times the solar value could support life provided they are hydrothermally active and fall within the habitable zone around the star.