Formation of H(2 )and CH(4 )by weathering of olivine at temperatures between 30 and 70°C

Hydrocarbons such as CH(4 )are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH(4 )through its redox lowering and water splitting properties. Knowledge about the CH(4 )and H(2 )formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH(4 )and for CO(2 )sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH(4 )and H(2 )formation potential of forsteritic olivine. The results show low temperature CH(4 )production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH(4 )source trapped in the crystal structure of the olivine showed no signs of incorporated CH(4). Also, the available sources of organic carbon were not enough to support the total amount of CH(4 )detected in our experiments. There was also a linear relationship between silica release into solution and the net CH(4 )accumulation into the incubation bottle headspaces suggesting that CH(4 )formation under these conditions could be a qualitative indicator of olivine dissolution. It is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze the formation of CH(4), because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH(4 )formation both on Earth and on other terrestrial bodies.