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Physical Environment > Ice Ages |
This site tells the story of the history of the universe. Click Earlier and Later to follow the story. Note: Many facts have been simplified to make them easier to understand. |
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During most of history the climate was warm (much warmer than today), the continents were flat and mostly covered by warm shallow seas, and there was no ice anywhere on Earth. But every 250 million years or so an ice age begins.
During an ice age, ice forms on the mountains and flows down in frozen rivers called glaciers. They wear away the mountains, grinding out valleys and carrying bits of rock down to the lower land. There the ice spreads out in sheets. Some of it reaches the sea and breaks off as icebergs. Remember that ice expands when it freezes into ice. That is why icebergs float. This is very lucky. If ice sank then all the oceans would freeze solid and life would be impossible. Sometimes the ice is thick and covers a lot of land. This is a glacial period and it lasts about ten thousand years. At other times most of the ice melts, covering only the tops of mountains and the poles. This is an inter-glacial, and it lasts about twenty thousand years or more. We are in one of these now. Each ice age is made up of several glacials and interglacials. The changes from glacial to interglacial and back again are probably caused by changes in the way the Earth moves round the Sun. This changes the amount of sunlight reaching the Earth. After a few million years the ice age ends, all the ice melts, and the weather goes back to its normal warm state. What causes an ice age? |
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Physical Environment > Ice Ages |
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Basic Information |
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