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What Started the Ice Age?
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# : |
16700 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
10 / 1989 |
2,979 Words |
| Author
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Marc J. Defant
Marc J. Defant is professor of geology at the University of
South Florida. He specializes in the study of volcanoes and is
the author of Voyage of Discovery: From the Big Bang to the
Ice Ages, a panoramic history of the universe, including our
galaxy, solar system, and planet. |
Woolly mammoths preserved by conditions during the last glacial era have long been surrounded in legend. Their ivory, particularly from the frozen wastelands of Siberia, is considered sacred and has been a commodity of trade throughout the world. Folklore even has it that many people throughout the centuries have tried to feast on preserved mammoth meat.
The intrigue surrounding preserved mammoths is merely part of man's deeper fascination with the glacial age and its mysteries. Since the realization that such glacial periods have occurred regularly in the past, scientists have tried to discover their cause. Evidence has mounted that glacial ages result from periodic changes in the way the earth orbits the sun. In addition, recent data suggest that the Ice Age began around 2.5 million years ago due to the uplift of two large plateaus on nearly opposite sides of the earth.
A Unique Time on Earth
Geologists know that the earth's climate has been colder than it is today at many times in the past because evidence of extensive glaciation exists in the geologic record. Both the woolly mammoth and the Alaskan steppe bison were frozen during the time of the last Neanderthals in Europe, when both Eurasia and North America were in the throes of the Ice Age. However, the ice receded during a warming trend that began approximately 17,000 years ago, so that by 7,000 years ago the glaciers had retreated to their present positions.
Massive ice sheets have advanced and retreated dozens of times during the last 2.5 million years. Many scientists believe that
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