Fig. 2.

Model steady states at 1,000 Ma as a function of terrestrial weatherability, W. Line type shows choices for the dependency of seafloor weathering rate on atmospheric CO₂ concentration. Rates of silicate and seafloor weathering (A), relative ocean phosphate concentration (B), organic carbon burial rate (C), the fraction of carbon buried organically (D), relative atmospheric oxygen (E), and CO₂ concentrations (F). Weatherability is defined as the global weathering flux that would be expected under present-day conditions, relative (i.e., normalized) to the present-day flux. Gray vertical line denotes best guess for W at 1,000 Ma. We assume a relative spreading rate and solar forcing of 1.83 (37) and 0.923 (38), respectively.