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| Ice
sheets form on top of glaciers and icebergs. They are made up
of hundreds or maybe thousands of years of snowfall. As the
layers of snow piles up on top of each other the bottom layers
are squashed into sheets of ice. Snow is formed into ice because
the weight of the layers on top squishes out the air that is
between the snow crystals. The bottom layers are thinner and
icier than the layers on top. These ice sheets may pile up to
about 10,000 feet high. Sometimes ice sheets are white as snow
and sometimes not. Sometimes ice sheets are clear like ice,
or they have a blue color. About 5,200,000 square miles of the
earth are covered in ice sheets. |
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| About 65 million years ago the earth started cooling off and
ice sheets spread from the north and south poles onto the land.
Ice sheets also formed down mountainsides and met the ice sheets
at the bottom. In some places the mountains were almost covered
up by the glaciers. In Antarctica there are some mountains still
burried by glaciers with only the peaks
of the moutains sticking out.. About 65 percent of the earth
was covered in ice sheets then. |
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