Fig. 3.

The evolution of surface pressure and temperature and the partial pressure of CO₂ in the model as the solar luminosity evolves in the next 2.8 Ga from present. Before 0.9 Ga (dashed line), the quantities evolve as described in Caldeira and Kasting (8). After 0.9 Ga, the surface temperature and the partial pressure of CO₂ at the surface (P_CO2) are kept constant while the atmospheric pressure is lowered to compensate the temperature increase due to the increase in solar luminosity (see Models and Results). At ≈2.3 Ga (dash-dotted line), runaway greenhouse occurs, signaling the ultimate fate of the biosphere.