Methane Greenhouses and Anti-Greenhouses on the Early Earth

Presenter: James Kasting, Pennsylvania State University
When: October 14, 2003 12AM PDT

Methane was probably much more abundant in the low-O2
Archean/early Paleoproterozoic atmosphere, prior to 2.3 Ga, than it is
today. CH4 concentrations of 1000 ppm or more are predicted once
methanogenic bacteria had evolved. Greenhouse warming from this CH4 could
have been a major factor in offsetting reduced solar luminosity at that
time. However, if CH4 became more abundant than CO2, it would have
polymerized to form hydrocarbon smog in the stratosphere. This, in turn,
would have created an anti-greenhouse effect that cooled the surface. The
rise of O2 at 2.3 Ga wiped out most of this methane and may have triggered
the very deep (possibly global) Paleoproterozoic glaciations.

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