Formation of H2 and CH4by weathering of olivine at temperatures between 30 and 70°C

Abstract

Hydrocarbons such as CH₄ 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 CH₄ through its redox lowering and water splitting properties. Knowledge about the CH₄ and H₂ formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH₄ and for CO₂ sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH₄ and H₂ formation potential of forsteritic olivine.

The results show low temperature CH₄ production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH₄ source trapped in the crystal structure of the olivine showed no signs of incorporated CH₄. Also, the available sources of organic carbon were not enough to support the total amount of CH₄ detected in our experiments. There was also a linear relationship between silica release into solution and the net CH₄ accumulation into the incubation bottle headspaces suggesting that CH₄ 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 CH₄, because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH₄ formation both on Earth and on other terrestrial bodies.