Some bulk properties of the abiotic Earth as a function of time. (a) The global average surface temperature warms as the star gradually brightens. (b) The ground albedo increases as dark ocean water subducts into the mantle and comparatively brighter land becomes exposed. The total albedo also increases as the warming planet’s atmosphere can hold more water vapor and more clouds form. (c) As the planet warms, the atmosphere can hold more water and the H₂O partial pressure increases. (d) Finally, atmospheric CO₂ spikes early on when the planet is cold, and gradually decreases as weathering becomes more efficient on the warming planet. On all plots, dots represent measurements of PIE (4.5 Gyr) properties with uncertainties.