Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth
- 3 August 2001
- journal article
- other
- Published by American Association for the Advancement of Science (AAAS) in Science
- Vol. 293 (5531) , 839-843
Abstract
The low O 2 content of the Archean atmosphere implies that methane should have been present at levels ∼10 2 to 10 3 parts per million volume (ppmv) (compared with 1.7 ppmv today) given a plausible biogenic source. CH 4 is favored as the greenhouse gas that countered the lower luminosity of the early Sun. But abundant CH 4 implies that hydrogen escapes to space (↑space) orders of magnitude faster than today. Such reductant loss oxidizes the Earth. Photosynthesis splits water into O 2 and H, and methanogenesis transfers the H into CH 4 . Hydrogen escape after CH 4 photolysis, therefore, causes a net gain of oxygen [CO 2 + 2H 2 O → CH 4 + 2O 2 → CO 2 + O 2 + 4H(↑space)]. Expected irreversible oxidation (∼10 12 to 10 13 moles oxygen per year) may help explain how Earth's surface environment became irreversibly oxidized.Keywords
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