Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth

摘要: 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 greenhouse gas countered lower luminosity early Sun. But abundant hydrogen escapes space (↑space) orders magnitude faster than today. Such reductant loss oxidizes Earth. Photosynthesis splits water into and H, methanogenesis transfers H CH4. Hydrogen escape after photolysis, therefore, causes net gain oxygen [CO2 + 2H2O → 2O2 CO2 4H(↑space)]. Expected irreversible oxidation (∼1012 1013 moles year) may help explain how Earth9s surface environment became irreversibly oxidized.