The report, published in the journal Science, said the finding challenges the generally accepted belief that substantial ice sheets could not have existed on Earth during major climate warming periods.

Researchers at Scripps Institution of Oceanography at the University of California, San Diego, examined geochemical and sea level data from marine microfossils deposited on the ocean floor 91 million years ago during the Cretaceous Thermal Maximum, which raised tropical ocean temperatures as high as 98.6 degrees Fahrenheit -- about 50 degrees warmer than today.

The research team found strong evidence to conclude that an ice sheet about half the size of the modern Antarctic ice cap existed for about 200,000 years, the university said Thursday in a release.

"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," co-author Richard Norris said. "This study demonstrates that even the super-warm climates of the Cretaceous Thermal Maximum were not warm enough to prevent ice growth."