Keywords:Archean, faint young Sun paradox, anaerobic organism, methane greenhouse effect, 1-D atmospheric chemistry - ocean ecosystem - biogeochemical cycle model
In the Archean, the climate of the Earth may have been warmer than that of today in spite of the lower luminosity of the Sun at that period . The greenhouse effect of methane, in addition to that of carbon dioxide, is considered to have maintained the warm climate [2, 3], however, previous studies do not support the methane flux required for the warm climate . In this study, we developed a coupled model of 1-D atmospheric chemistry – ocean ecosystem – biogeochemical cycle in order to investigate the biogenic methane flux in the Archean. We found that the biogenic methane flux could have been high enough to maintain warm climate if we assume ecosystem composed of multiple anoxygenic phototrophs which uses hydrogen and iron, with acetogen and methanogens, because of the H2–CH2O–CH4 and CO–CH3COOH–CH4 biogeochemical cycles driven by Fe-CH2O-CH4 biogeochemical cycle could amplify the methane production nonlinearly through the recycling processes of organic matters.
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