Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth
Abstract
The low O2 content of the Archean atmosphere implies that methane should have been present at levels ~102 to 103 parts per million volume (ppmv) (compared with 1.7 ppmv today) given a plausible biogenic source. CH4 is favored as the greenhouse gas that countered the lower luminosity of the early Sun. But abundant CH4 implies that hydrogen escapes to space (↑space) orders of magnitude faster than today. Such reductant loss oxidizes the Earth. Photosynthesis splits water into O2 and H, and methanogenesis transfers the H into CH4. Hydrogen escape after CH4 photolysis, therefore, causes a net gain of oxygen [CO2 + 2H2O --> CH4 + 2O2 --> CO2 + O2 + 4H(↑space)]. Expected irreversible oxidation (~1012 to 1013 moles oxygen per year) may help explain how Earth's surface environment became irreversibly oxidized.
- Publication:
-
Science
- Pub Date:
- August 2001
- DOI:
- 10.1126/science.1061976
- Bibcode:
- 2001Sci...293..839C
- Keywords:
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- GEOCHEM PHYS