Despite a fainter Sun , the surface of the early Earth was mostly ice-free .
Proposed solutions to this so-called ” faint young Sun problem ” have usually involved higher amounts of greenhouse gases than present in the modern-day atmosphere .
However , geological evidence seemed to indicate that the atmospheric CO _ { 2 } concentrations during the Archaean and Proterozoic were far too low to keep the surface from freezing .
With a radiative-convective model including new , updated thermal absorption coefficients , we found that the amount of CO _ { 2 } necessary to obtain 273 K at the surface is reduced up to an order of magnitude compared to previous studies .
For the late Archaean and early Proterozoic period of the Earth , we calculate that CO _ { 2 } partial pressures of only about 2.9 mb are required to keep its surface from freezing which is compatible with the amount inferred from sediment studies .
This conclusion was not significantly changed when we varied model parameters such as relative humidity or surface albedo , obtaining CO _ { 2 } partial pressures for the late Archaean between 1.5 and 5.5 mb .
Thus , the contradiction between sediment data and model results disappears for the late Archaean and early Proterozoic .