Estimates of atmospheric CO2 in the Neoarchean-Paleoproterozoic from paleosols

The new method was then applied to eight paleosols formed in the Neoarchean-Paleoproterozoic. We made constraints on the local temperatures, at which the paleosols were formed, mainly by the temperature and solute-concentration relationships in the literature, because they should have been different between the paleosols and from the average global surface temperatures. Under the constrained local temperatures, the PCO2 levels were calculated to be 85-510 times the present day atmospheric level (PAL) at ∼2.77 Ga, 78-2500 PAL at ∼2.75 Ga, 160-490 PAL at ∼2.46 Ga, 30-190 PAL at ∼2.15 Ga, 20-620 PAL at ∼2.08 Ga and 23-210 PAL at ∼1.85 Ga. The estimated PCO2 levels are higher than those to maintain the average global surface temperature of the Earth above the freezing point of water only by CO2 itself. The newly estimated PCO2 levels probably imply that atmospheric CO2 decreased gradually in long term in the Neoarchean-Paleoproterozoic and that the glaciations at ∼2.9 and ∼2.4-2.2 Ga were differently triggered.