Cenozoic Climate ^ Oxygen Isotope Evidence

Discoveries of fossil remains of 50 million year old alligators on Ellesmere Island and 30}40 million year-old forests on Antarctica contrast sharply with our present vision of polar climates. These are not isolated discoveries or quirks of nature. An evergrowing body of faunal, Soral, and geochemical evidence shows that the Rrst half of the Cenozoic Era was much warmer than the present time. What maintained such a warm climate and could it be an analog for future global warming? To address these and other questions, one needs more than a qualitative estimate of planetary temperatures. Quantitative temperature estimates (both magnitudes and rates of change) are required to depict how the Earth’s climate has changed through time. One of the most powerful tools used to reconstruct past climates during the Cenozoic (the last 65 million years of Earth’s history) is the analysis of oxygen isotopes in the fossil shells of marine organisms. The calcium carbonate shells of the protist foraminifera are the most often analyzed organisms because the different species are distributed throughout surface (planktonic) and deep (benthic) marine environments.