Purdue University (2011, December 1). Drop in carbon dioxide levels led to polar ice sheet, study finds. ScienceDaily Citat: "...For 100 million years prior to the cooling, which occurred at the end of the Eocene epoch, Earth was warm and wet...Then, over a span of about 100,000 years, temperatures fell dramatically, many species of animals became extinct, ice covered Antarctica and sea levels fell as the Oligocene epoch began...What drove the rise and fall in carbon dioxide levels during the Eocene and Oligocene is not known..."
