Concentration of carbon dioxide in the Late Cretaceous atmosphere

Stable carbon isotope data from Late Cretaceous (Maastrichtian) palaeosols in India are used to estimate the concentration of carbon dioxide in the Late Cretaceous atmosphere. We show that the Maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of CO2. This value agrees with an independently modelled value of CO2 in the Late Cretaceous atmosphere. A low concentration of the greenhouse gas carbon dioxide in the Maastrichtian atmosphere (relative to concentrations in the earlier Cretaceous) is consistent with palaeotemperature information from terrestrial plant and marine fossils, which suggest that the global climate cooled toward the end of the Cretaceous Period.