Models of the carbon cycle, used to calculate atmospheric CO2 levels and mean global surface temperatures over geologic time, rely heavily on estimates of CO2 consumed by chemical wethering. Weathering of calcium and magnesium silicates is the primary sink for atmospheric CO2, yet alkali feldspar dissolution rates of data from carbonate aquifers have generally been used as model inputs instead. The latter causes calculated CO2 levels and temperatures to be anomalously high in the model of Berner et al. (1983) (for example, temperature of 24¿C and 19¿C are calculated for the Cretaceous and Eocene, respectively). When Ca and Mg silicate weathering rates are used as primary inputs instead, ambient temperatures and atmospheric CO2 levels are calculated to be significantly closer to recent preindustrial level (global mean temperatures of ~20.5¿C and 17.5¿C in the Cretaceous and Eocene, respetively), indicating an appreciably tighter coupling between chemical weathering and climate. ¿American Geophysical Union 1991