Abstract
High concentrations of greenhouse gases would have been required to offset low solar luminosity early in Earth9s history. Enhanced CO 2 levels are probably at least part of the solution, but CH 4 may have played a significant role as well, particularly during the Late Archean era, 2.5–3.0 Ga, when methanogenic bacteria were almost certainly present. Indeed, biological CH 4 production should have led to CO 2 drawdown by way of a negative feedback loop involving the carbonate-silicate geochemical cycle. We suggest here that the atmospheric CH 4 /CO 2 ratio approached the value of ∼1 needed to trigger formation of Titan-like organic haze. This haze was strongly depleted in 13 C relative to 12 C and was produced at a rate comparable to the modern rate of organic carbon burial in marine sediments. Therefore, it could provide a novel explanation for the presence of extremely low- 13 C kerogens in Late Archean sediments.
Published Version
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