Synthesis of H2 on Terrestrial Planetary Surfaces

Details Synthesis of H2 on Terrestrial Planetary Surfaces Synthesis of H2 on Terrestrial Planetary Surfaces

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.v43d..03s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #V43D-03

Other

5215 Origin Of Life, 5220 Hydrothermal Systems And Weathering On Other Planets, 0412 Biogeochemical Kinetics And Reaction Modeling (0414, 0793, 1615, 4805, 4912), 0450 Hydrothermal Systems (1034, 3017, 3616, 4832, 8135, 8424), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008)

Scientific paper

The geochemical formation of molecular hydrogen (H2) is a fundamental process relevant to the inorganic synthesis of organic compounds, the origins of early life, and as an energy source for a broad array of chemosynthetic organisms. Perhaps the most important reaction capable of producing copious amounts of H2 near terrestrial planetary surfaces is the hydration of olivine (sepentinization) observed in hydrothermal systems and laboratory studies. During this reaction, H2 is produced through the reduction of H2O that accompanies oxidation of Fe2+ in olivine. The relationship between olivine composition and H2 production through serpentinization is not well-defined; however, it is generally assumed that more Fe in olivine will produce more H2. Here, we evaluate how the composition of olivine in the forsterite (Mg2SiO4)-fayalite (Fe2SiO4) binary system governs the production of H2 via serpentinization reactions over a range of pressures (1 bar to 5 kbar) and temperatures (0-500 °C). We used SUPCRT92 to model the geochemical thermodynamics of serpentinization reactions at elevated pressures and temperatures. Our results demonstrate that less Fe2+ in olivine will produce more H2. Accordingly, olivine compositions on Earth (~Fo90) are anticipated to promote a fast and thermodynamically favorable route towards elevated levels of H2. In comparison, Martian olivines contain more Fe with compositions between Fo40-Fo70, which would greatly reduce the heat and H2 generated during serpentinzation. If abiotic carbon fixation is a basic step towards origin and sustenance of life and serpentinization is a key reaction, then our calculations suggest that life should have a chance to succeed on rocky, volcanic, wet planets where olivine compositions are greater than Fo50 and less than Fo100 and would require alternative routes when compositions are less than Fo25.

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