tokens: Earth) for different ocean coverages. Panel B shows how pCO 2 varies with varied solar luminosity for different ocean coverages. Both Panel A and B assume an Earth-like outgassing rate of CO 2 . We did not plot solar luminosities greater than 1.2 S eff as the weathering rate dependence on CO 2 becomes negligible. Panel C shows how the surface temperature varies with varied CO 2 outgassing rates (relative to modern Earth) for different ocean coverages. And Panel D shows how pCO 2 varies with varied outgassing rates for different ocean coverages. Panel C and D assume a modern Earth solar constant. All panels assume a fixed planetary albedo of α = 0.3. Based on the results from Figure 1 , a planet’s buffering capability changes significantly when seafloor weathering becomes the dominant weathering sink, due to the different pCO 2 dependencies of seafloor versus continental weathering. We therefore determine the critical ocean fraction where weathering behavior switches from being dominated by seafloor weathering to being dominated by continental weathering by setting F cw = F sw , and solving for the ocean fraction: We solve for this critical ocean fraction for a range of solar luminosities, setting the rest of the variables equal to the median values that we used for Figure 1 , as a function of pCO 2 (see Figure 2 ). The solid curves in Figure 2 correspond to the at which the weathering fluxes from continental weathering and seafloor weathering are equal. While we calculated over a range of pCO 2 values, only certain pCO 2 pressures would be physical for a given solar luminosity using our weathering model. The dashed curves with the points are from our previous results, where we calculated the actual pCO 2 of a planet given its solar luminosity and ocean fraction (see Figure 1 ). Figure 2. The solid curve represents the ocean fraction at which seafloor weathering and continental weathering are equal, as a function of pCO 2 . We solved this critical ocean fraction curve for different solar luminosities and found that the difference was negligible (the black curve shown is for an S eff of 1.0). If a planet’s ocean coverage is above the curve, then seafloor weathering is the dominant sink of CO 2 , and if a planet’s ocean coverage is below the curve, then continental weathering is the dominant sink of CO 2 . The colored curves and points are data from Figure 1 , allowing us to constrain this parameter space by plotting the actual pCO 2 values that our model converged toward for a given ocean fraction and solar luminosity. We find that for solar luminosities lower than modern Earth’s, an ocean fraction of greater than 90% is needed for seafloor weathering to equal continental weathering. What we find from Figure 2 is that for relative solar luminosities less than or equal to S eff = 1.0, the planet requires an ocean fraction between 90% and 99% for the CO 2 flux from seafloor weathering to equal the CO 2 flux from continental weathering. This is
ner_tags: O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O O O B-EntityOfFutureInterest O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O O O O O O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O B-EntityOfFutureInterest I-EntityOfFutureInterest O O O O O B-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O