The new study examines geochemical and sea level data retrieved from marine microfossils deposited on the ocean floor 91 million years ago during the Cretaceous Thermal Maximum (also known as the super-greenhouse). This extreme warming event in Earth's history raised tropical ocean temperatures to 35-37°C (95-98.6°F), about 10°C (50°F) warmer than today, thus creating an intense greenhouse climate.
The study found strong evidence that an ice sheet about 50-60 percent the size of the modern Antarctic ice cap existed for about 200,000 years. "Until now it was generally accepted that there were no large glaciers on the poles prior to the development of the Antarctic ice sheet about 33 million years ago," said study co-author Richard Norris. "This study demonstrates that even the super-warm climates of the Cretaceous Thermal Maximum were not warm enough to prevent ice growth."
Paradoxically, past greenhouse climates may have aided ice growth by increasing the amount of moisture in the atmosp
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