Welcome to You Ask Andy

Dan Connero ale 13, of Chula Vista Ca

What started the last cycle of Ice Ages?

We tend to think that the Ice Age climate was .shivering cold, summer and winter. But modern experts tell us that this was most likely not so at a11, Where the ice sheets gathered, the year round climate may have been only 10 or 15 degrees cooler than it is today.

The winters would not have to be very cold, just cold enough to bring ice and snow. A few summer days could have been quite hot. Buts through the centuries, the summers were not long enough or warm enough to melt all of the winter snow and ice, Year by year, century by century, the bulk of ice and snow on the ground grew and grew. When the layers of ice became 150 feet thick.. they began to spread out and behave like glaciers: It was a gradual process and the Ice Age glaciers grew slowly over thousands of years.

No one knows for sure what caused floe climate of the world to cool the few necessary degrees for the glaciers to form. There are several theories: but not enough evidence to prove any one of them. Some experts think that the atmosphere may have screened out some of the sun's heat. Perhaps there were clouds of dust in the air. A rash of volcanic activity could cause this. Perhaps there were extra quotas of carbon dioxide in the air. This too could come from volcanoes. But there is no evidence to prove that either of these factors were preset.

A newer theory suggests that the Ice Ages were caused by the sun. Perhaps there were times when 01d Sol gives off less heat, in which case the Earth would be cooler. But there is no evidence to prove this theory either.

At the present time we are emerging from an Ice Age. Ours is a spring time climate. Many icefields are noticeably shrinking and many experts think that the glaciers and stubborn ice fields of Greenland and Antarctica are also doomed to melt away.

In the last ten million years, four Ice Ages gave gripped the northern land masses. They land masses. They were separated by long periods of warm climate, as warm or warmer than the one we enjoy, The last Ice Age was in full spring about 100,000 years ago. At that time it was estimated that 12 million square miles of land were crushed under the glaciers.  In vast areas the ice was two to three miles thick.

This most recent Ice Age bet an to lose its grip about years ago. About 30,000 years ago, the ice was withdrawing from the region of the Great Lakes. New England was freed frora the icy Trip about 28,000 years ago. The, ice was beginning to melt away from Minnesota about 15,000 years ago.

Experts can trace the story of each Ice Age. Some of them date back to the early ages of earth's history. We have a very good idea of what they did, where they went and how long they lasted, But so far no one can prove what caused them. Perhaps some young person in your geology class will grow up to solve this teasing problem.

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