SERPENTINIZATION AND THE INORGANIC SYNTHESIS OF H2 ON 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 (serpentinization). Here, we evaluate how the composition of olivine in the forsterite (Mg₂SiO₄)-fayalite (Fe₂SiO₄) binary system governs the production of H₂ via serpentinization reactions over a range of pressures (1 bar to 5 kbar) and temperatures (0-500^oC) using the geochemical modeling program SUPCRT92. Our results demonstrate that less Fe²⁺ in olivine will produce more H₂ where copious amounts of H₂ are produced only when the olivine undergoing alteration (serpentinization) contains 1 to 50 mole percent Fe. In general, life should have a chance to succeed on rocky, volcanic planets where olivine compositions are greater than Fo₅₀ and less than Fo₁₀₀ and would require alternative routes when compositions are less than Fo₂₅.