Biogenic methane, hydrogen escape, and the irreversible oxidation of early Earth

The low O-2 content of the Archean atmosphere implies that methane should have been present at levels similar to 10(2) to 10(3) 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 (up arrow 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 CH4. Hydrogen escape after CH4 photolysis, therefore, causes a net gain of oxygen [CO2 + 2H(2)O CH4 --> 2O(2) --> CO2 + O-2 + 4H(up arrow space)]. Expected irreversible oxidation (similar to 10(12) to 10(13) moles oxygen per year) may help explain how Earth's surface environment became irreversibly oxidized.