Organic haze in Earth's early atmosphere: Source of low-C-13 Late Archean kerogens?

High concentrations of greenhouse gases would haven been required to offset low solar luminosity early in Earth's history. Enhanced CO2 levels are pro bably at least part of the solution, but CH4 may have played a significant role as well, particularly during the Late Archean era, 2.5-3.0 Ga, when me thanogenic bacteria were almost certainly present. Indeed, biological CH4 p roduction should have led to CO2 drawdown by way of a negative feedback loo p involving the carbonate-silicate geochemical cycle. We suggest here that the atmospheric CH4/CO2 ratio approached the value of similar to1 needed to trigger formation of Titan-like organic haze. This haze was strongly deple ted in C-13 relative to C-12 and was produced at a rate comparable to the m odern rate of organic carbon burial in marine sediments. Therefore, it coul d provide a novel explanation for the presence of extremely low-C-13 keroge ns in Late Archean sediments.