Mineralogical constraints on Precambrian pCO2.

Arising from M. T. Rosing, D. K. Bird, N. H. Sleep & C. J. Bjerrum 464, 744-747 (2010)Rosing and others recently proposed a new model for the early Earth's atmospheric composition. They suggest, on the basis of mineral assemblages in sedimentary rocks, that atmospheric CO₂ and CH₄ concentrations have been consistently overestimated. This proposal is intriguing, given that high concentrations of these gases are traditionally considered to be the solution to the 'faint young Sun paradox' of why the Earth did not freeze over in our Sun's youth when solar luminosity was greatly decreased. Rosing and others instead invoke a decreased planetary albedo during the Earth's early history. New insights into this problem, which has long captivated those interested in the Earth's early climate and biological history, are welcome. However, we believe that the arguments presented by Rosing and others for roughly modern values of the partial pressure of CO₂ () are not robust. [ABSTRACT FROM AUTHOR]