Supercritical carbon dioxide likely served as a prebiotic source of methanethiol in primordial ocean hydrothermal systems

Abstract Abiotic synthesis of methanethiol through CO2 reduction is a presumptive initiation reaction of protometabolism in primordial ocean hydrothermal systems. However, reported artificial means of methanethiol production indicate the necessity of gas-phase condition, rather than aqueous-phase setting, for this prebiotic reaction to occur. Here we show that, under supercritical CO2 with a geochemically feasible concentration of hydrogen, up to 7.9% conversion of hydrogen sulfide to methanethiol is attained through a 14-day reaction at 200 °C on molybdenum sulfide catalyst deposited in a carbonate-NaCl solution. On the present ocean floor, discharges of liquid/supercritical CO2 occasionally occur in close vicinity to hydrothermal vents. Geological records of ancient seafloor suggest prevalence of such CO2 fluxes associated with hydrothermal activities. Our experimental results link these facts with the protometabolism scenario, leading to the possibility that the generation and transportation of methanethiol through the subseafloor CO2 fluxes constituted the beginning step of protometabolism in primordial ocean hydrothermal systems. Thus, the supply of supercritical-CO2-derived materials likely assisted the chemical evolution of life in combination with the known geochemical processes at the vent-ocean interface.