Use of carbon isotopes in paleosols as an indicator of the P(CO₂) of the paleoatmosphere

Measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo‐P(CO 2 ) content of the paleoatmosphere. Measurements from Tertiary paleosols indicate that the levels of CO 2 in the early Eocene, middle and late Miocene, and Pliocene were less than 1000 ppmV. Early Cretaceous levels of P(CO 2 ) were significantly higher, of the order of 1500 to 3000 ppmV.