In situ high-pressure and high-temperature bubble growth in silicic melts

In the presence of water, olivine of ultramafic rock is oxidized during the process referred to as `serpentinizationʹ. Water in contact with the olivine is reduced to molecular hydrogen (H2) with the concomitant oxidation of Fe(II). The molecular hydrogen formed may be used as an energy source by lithotrophic bacteria, but may, at high temperature, also be combined with CO2 for the abiotic formation of organic compounds such as hydrocarbons and fatty acids through Fischer¯Tropsch type (FTT) synthesis. Our analyses of fluids from the peridotitehosted Rainbow hydrothermal field on the Mid-Atlantic Ridge indicate de novo synthesis of linear saturated hydrocarbons. The chain length of the hydrocarbons is between 16 and 29 carbon atoms. The discovery of FTT reactions in ultramafic hydrothermal systems on Earth provides an alternative pathway for the formation of early membranes and the origin of life.