A hydrogen-dependent geochemical analogue of primordial carbon and energy metabolism

Hydrogen gas, H-2, 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. H-2 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 H-2 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 H-2 at 100 degrees C under alkaline aqueous conditions. The product spectrum includes formate (up to 200 mM), acetate (up to 100 mu M), pyruvate (up to 10 mu M), methanol (up to 100 mu M) 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. Three iron minerals found in alkaline hydrothermal vents are shown to convert CO2 and H-2 into formate, acetate and pyruvate in water, suggesting that such reactions could have paved the way for early metabolism.