CO2 drawdown and cooling at the onset of the Great Oxidation Event recorded in 2.45 Ga paleoweathering crust

Abstract

The Archean atmosphere is thought to have been devoid of oxygen but, instead, containing high concentrations of greenhouse gases, such as CO2 and possibly CH4, that were required to keep the Earth surface environments warm enough for maintenance of liquid water under faint-young-Sun conditions. Earlier studies have suggested that the CO2 concentrations must have been as high as over 1000 times present atmospheric levels (PAL) to overcome the effects of weaker solar luminosity. However, more recent studies of Precambrian paleosols imply existence of at least tenfold-lower, but still high pCO2 levels. The appearance of minute amounts of atmospheric O2 at the transition of Archean and Proterozoic is well documented, however, the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated. Different paleoclimate proxies of the ~2.45 Ga Kuksha paleoweathering crust suggest its formation in a cool, temperate climate. Paleoatmospheric pCO2 estimates by geochemical and isotopic mass-balance models suggest remarkably low paleoatmospheric CO2 levels, with the best guess estimates of atmospheric CO2 between 1 and 10 PAL. We speculate that the Kuksha paleoweathering crust either predates, or partly overlaps with, the onset of Huronian glaciation and corresponds to a time interval of low CO2 level during the first recorded large glaciation in Earth history.