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Stones crush standard ice history.

Fighting off icebergs and paint-stripping gales, an international drilling expedition off the southeast coast of Greenland has pulled up layers of ocean sediments that rewrite the glacial history of the Arctic region.

Large stones found amid the finegrained, muddy sediment indicate that ice covered sections of Greenland much earlier than scientists had previously suspected.

Climate experts know that the Earth has faded in and out of an extended ice age for the last 2.6 million years. Some times, such as the present, have had relatively warm climates, with giant glaciers surviving only on Greenland and Antarctica. Yet during most of this glacial span, ice sheets have extended across Scandinavia, Canada, and parts of the United States as well.

The new evidence suggests that some of the northern hemisphere's ice sheets began growing as far back as 7 million years, according to Hans Christian Larsen of the Geological Survey of Greenland in Copehagen, Denmark.

Larsen served as one of the chief scientists during the six-week-long drilling effort near Greenland, part of the ongoing, multination Ocean Drilling Program. Last month, ODP announced the results obtained from the voyage.

The large stones discovered in the drill cores provide the clue that Greenland had at least a partial ice cover, Larsen says.

The rocks indicate that icebers must have plied this part of the North Atlantic, because such large stones could not have reached a deep ocean site except by hitching a ride within a floating berg. The ice would have broken off glaciers on Greenland and drifted out to sea, dropping larges stones along the way as it melted.

The crew encountered harsh conditions while drilling in October and November. As if to underscore the glacial evidence found in the sediments, icebergs assaulted the ship several times, forcing the team to abandon its drilling and move the vessel. Winds of up to 80 knots and subfreezing air temperatures combined to strip paint off the boat, says Larsen.

The new findings surprised Larsen and his collegues because earth scientists have long thought that the Arctic was relatively warm up until 3 million years ago.

While the Arctic Ocean today is largely covered by sea ice, evidence suggests that the ocean remained open for at least part of the year prior to 3 million years ago. Scientists have also found evidence of forests existing during this time in Iceland.

Kenneth G. Miller of Rutgers University in Piscataway, N.J., says the new results provide hard evidence that ice sheets started growing in the northern hemisphere much earlier than most scientists had thought. He and Larsen agree, however, that the main buildup of ice on North America did not occur until around 2.6 million years ago -- a time when the climate took a decidedly frosty turn.
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Title Annotation:Greenland's geological history
Author:Monastersky, Richard
Publication:Science News
Date:Jan 1, 1994
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