A coupled ecosystem-climate model for predicting the methane concentrationin the archean atmosphere

A simple coupled ecosystem-climate model is described that can predict leve ls of atmospheric CH4, CO2, and H-2 during the Late Archean, given observed constraints on Earth's surface temperature. We find that methanogenic bact eria should have converted most of the available atmospheric H-2 into CH4, and that CH4 may have been equal in importance to CO2 as a greenhouse gas. Photolysis of this CH4 may have produced a hydrocarbon smog layer that woul d have shielded the surface from solar UV radiation. Methanotrophic bacteri a would have consumed some of the atmospheric CH4, but they would have been incapable of reducing CH4 to modern levels. The rise of O-2 around 2.3 Ga would have drastically reduced the atmospheric CH4 concentration and may th ereby have triggered the Huronian glaciation.