The faint young sun problem

Abstract

It is shown that the faint young sun problem was most likely solved by an increase in atmospheric CO2 concentration in the earth's atmosphere brought about by the CO2 geochemical cycle. Because the loss process for atmospheric CO2 requires liquid water, and because the earth is continually resupplying atmospheric CO2 by carbonate metamorphism, the surface temperature should never have fallen below the point at which the ocean would freeze. Indeed, the early earth may have been quite warm if carbonate metamorphism was faster and if the continents were originally smaller, so that silicate weathering was inhibited.