A Revised, Hazy Methane Greenhouse for the Archean Earth

Jacob D. Haqq-Misra, Shawn D. Domagal-Goldman, Patrick J. Kasting, James F. Kasting
2008 Astrobiology  
Geological and biological evidence suggests that Earth was warm during most of its early history, despite the fainter young Sun. Upper bounds on the atmospheric CO 2 concentration in the Late Archean/Paleoproterozoic (2.8-2.2 Ga) from paleosol data suggest that additional greenhouse gases must have been present. Methanogenic bacteria, which were arguably extant at that time, may have contributed to a high concentration of atmospheric CH 4 , and previous calculations had indicated that a CH 4
more » ... ated that a CH 4 -CO 2 -H 2 O greenhouse could have produced warm Late Archean surface temperatures while still satisfying the paleosol constraints on pCO 2 . Here, we revisit this conclusion. Correction of an error in the CH 4 absorption coefficients, combined with the predicted early onset of climatically cooling organic haze, suggest that the amount of greenhouse warming by CH 4 was more limited and that pCO 2 must therefore have been Ն0.03 bar, at or above the upper bound of the value obtained from paleosols. Enough warming from CH 4 remained in the Archean, however, to explain why Earth's climate cooled and became glacial when atmospheric O 2 levels rose in the Paleoproterozoic. Our new model also shows that greenhouse warming by higher hydrocarbon gases, especially ethane (C 2 H 6 ), may have helped to keep the Late Archean Earth warm.
doi:10.1089/ast.2007.0197 pmid:19093801 fatcat:aftprz5ezrd5hfpqoejno5zufm