Sunsettommy
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Glaciers
Illinois Glacial History
EXCERPT:
Foreword
In approximately 4.6 billion years of Earth history, there have been three major episodes of glaciation. The Varangian glaciation occurred during the Proterozoic part of the Precambrian period about 700 million years ago (m.y.a.). The next one happened in the late Paleozoic Era around 300 m.y.a. The most recent period of glaciation started approximately 1.6 m.y.a. and ended about 10,000 years ago.
Today, glaciers contain nearly 75% of the world’s fresh water supply in ice that covers about 10% of land area. In contrast, ice covered as much as 30% of total land area during the most recent ice age. The largest concentration of ice today is the Antarctic ice sheet, up to 4,200 meters thick in some areas, and in the Greenland ice sheet. The remainder of glaciers is located in montane regions and in ice caps in polar seas. If climate were to suddenly warm enough to melt all land ice, there would be a eustatic sea level rise of about 70 meters. Sea level has risen about 100 meters since the last glacial maximum 20,000 years ago. Potential causes of Ice Ages and glacial cycles are variations in lithospheric plate configurations, changes in atmospheric and seawater circulation patterns, changes in atmospheric composition, and Milankovitch orbital variations.
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| 03-14-2010 12:41 AM |
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