"One of the most fundamental climate shifts that this planet has undergone since the events that precipitated the extinction of the dinosaurs is the so-called 'greenhouse to icehouse transition' - the time when Earth went from having virtually no ice on it at all to one with a more or less permanent ice sheet covering Antarctica," says Linda C. Ivany, professor of earth science in The College of Arts and Sciences at Syracuse University and principal investigator of a project aiming at understanding about how the ice sheet covering most of Antarctica really began.

"This happened about 34 million years ago, and is marked by dramatic changes in the chemistry of the oceans and the appearance of 'ice rafted debris' in ocean sediments around Antarctica, carried there by icebergs from land that floated out and melted far from the continent, releasing the sand and rock that had been frozen into them."

Scientists believe that the growth of the Antarctic ice sheet was initiated by a drop in greenhouse gas concentrations in the atmosphere in combination with a change in ocean circulation caused by South America pulling away from Antarctica. Researchers have now shown that these gradual changes caused faster changes than previously thought. Apparently, the Earth cooled fast enough to allow the growth of ice on the entire continent almost all at once.

Ivany's research team studied sediments on Seymour Island, off the northern tip of the Antarctic Peninsula, and found features characteristic of deposition by glacial ice. This is surprising because this island is at the far northern reaches of the Peninsula, in western Antarctica. These findings suggest that glaciations grew far more extensively and faster than originally suspected.

The scientists remarked that this discovery shows how dramatically Earth's climate system can shift in a short amount of time and said that their discovery may provide an insight into how things could change in the future if we continue to alter our environment.

Photo: sediments characteristic of deposition by glacial ice near the Eocene-Oligocene boundary on Seymour Island. Credit: Linda C. Ivany