Phanerozoic rates of diversification of the marine fauna and modeled levels of atmospheric CO₂ are closely correlated. Macroevolutionary origination rates from Sepkoski's (1998) marine animal database and pCO₂ from Berner and Kothavala's (2001) model of Phanerozoic atmospheric pCO₂ show a statistically significant correlation (p < 0.001). Phanerozoic rates of marine animal extinction are also correlated with atmospheric CO2 (p < 0.01). These strong correlations suggest that one or more environmental variables controlling pCO₂ levels have had a profound impact on evolution throughout the history of metazoan life or that CO₂ directly affects macroevolution. Paleotemperature may be an intermediary between the two; decreased CO₂ may be associated with decreased temperature which may have led to decreases in marine diversification. Yet another hypothesis is that enhanced CO₂ levels may be associated with increased seafloor spreading rates, encouraging biological diversification by isolating faunas. D. H. Rothman (2001) Proc. Natl. Acad. Sci. USA 98:4305-4310 has also described a correspondence between large scale evolutionary trends and geochemical parameters. He showed that for the last 400 million years the diversity of marine animals has a significant (p < 0.001) negative correlation with the stable carbon isotope fractionation between total organic carbon and sedimentary carbonates. The correspondences between geochemical and biological history strongly suggest that the overall controls on most of the macroevolutionary levels are environmental variables rather than intrinsic biotic controls.