9:00 AM - 9:20 AM
[BBG02-01] Primitive microbial ecosystem and the faint young Sun paradox
Keywords:Archean, faint young Sun paradox, methane
Primary productivity in the Archean ocean is important to estimate CH4 flux to the atmosphere, because CH4 was produced from activity of methanogen. Primitive photosynthetic bacteria, which did not produce oxygen, were probably primary producers in the Archean oceans. They probably used H2 and Fe2+ as a electron donor for photosynthesis. We therefore try to estimate CH4 flux and concentration in the atmosphere with a coupled model of primitive microbial ecosystem, photochemical reactions, biogeochemical cycle, and climate.
We found that, the CH4 flux to the atmosphere is too low to form warm climate when only one photosynthesizer (H2-based or Fe-based anoxygenic photoautotroph) is considered in the ecosystem, but the CH4 flux becomes enough to create warm climate when hybrid ecosystem of H2-based and Fe-based anoxygenic photoautotrophs is considered. This is because of a nonlinear amplification of methane cycle due to nonlinear increases of CH4 and H2 concentrations in the atmosphere against increase of CH4 flux.
We conclude that diversity of primitive anoxygenic photoautotrophs was important for stabilization of warm climate in the Archean. It also implies that microbial activity and CH4 are important to understand environment of young Earth-like habitable planets in the exoplanetary systems.