Serpentinization of olivine with Fe-Ni alloys: Implications for hydrogen(H₂) generation and the early earth atmosphere

erpentinization of ultramafic rocks， particularly olivine-rich peridotite， was a fundamental and globally extensive process on the early Earth that sustained vigorous hydrogen (H₂) generation. Although iron meteorite-delivered Fe-Ni alloys are generally considered volumetrically minor and spatially restricted， their high reactivity in hydrothermal systems may have critically influenced local H₂ and hydrocarbon budgets. Here， we simulate such environments experimentally by reacting mechanical mixtures of olivine and Fe-Ni alloys (FeNi and Fe_1.95Ni) at 300 ℃ and 3.0 kbar. Serpentinization replaces olivine with chrysotile， yielding substantial H₂ （85-230 mmol/kg）. Compared to olivine-only experiments， the alloys enhance H₂ production， indicating alloy consumption during serpentinization. Using the equilibrium between dissolved and gaseous H₂， we quantify oxygen fugacities (fO₂) at ΔFMQ -4.02 to -4.75 （relative to the fayalite-magnetite-quartz buffer）. Alloys were progressively consumed， leaving ～11 wt% of the initial mass. Although alloys slightly retard serpentinization kinetics， their compositions remain nearly constant across the investigated fO₂ range. These findings explain the extreme scarcity of Fe-Ni alloys in natural serpentinites and underscore H₂-mediated control of serpentinization kinetics. More broadly， they demonstrate that even minor， localized meteoritic alloy inputs can generate intense H₂ pulses， substantially contributing to the maintenance of an anoxic early-Earth atmosphere over geological timescales.