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 climates. An ever-growing body of faunal, floral, and geochemical evidence shows that the first half of the Cenozoic Era and earlier parts of Earth History were much warmer than the present. What maintained such a warm climate, and could it be an analog for future global warming? To address such questions, one needs quantitative temperature estimates: one needs to know both magnitudes and rates of change to depict how the Earth’s climate has changed through time. One of the most powerful tools 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 calcium carbonate shells of marine organisms.