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Abstract

Hydrogen gas, H₂, is generated by alkaline hydrothermal vents through an ancient geochemical process called serpentinization, in which water reacts with iron-containing minerals deep within the Earth’s crust. H₂ is the electron donor for the most ancient and the only energy-releasing route of biological CO₂ fixation, the acetyl-CoA pathway. At the origin of metabolism, CO₂ fixation by hydrothermal H₂ within serpentinizing systems could have preceded and patterned biotic pathways. Here we show that three hydrothermal minerals—greigite (Fe₃S₄), magnetite (Fe₃O₄) and awaruite (Ni₃Fe)—catalyse the fixation of CO₂ with H₂ at 100 °C under alkaline aqueous conditions. The product spectrum includes formate (up to 200 mM), acetate (up to 100 µM), pyruvate (up to 10 µM), methanol (up to 100 µM) and methane. The results shed light on both the geochemical origin of microbial metabolism and the nature of abiotic formate and methane synthesis in modern hydrothermal vents.