Fig. 3.

Model steady states at 1,000 Ma as a function of relative seafloor spreading rate. 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). Gray vertical line denotes assumed spreading rate at 1,000 Ma (37). We assume a terrestrial weatherability and solar forcing of 1/4 (12) and 0.923 (38), respectively.