1. There have been approximately 11 different ice ages that have
occurred during the earth's 4.6 billion years of existence. The
last ice age was called "The Great Ice Age", and it occurred
11,000 years ago. During the "Great Ice Age" over a third of the
earth was covered in ice, and the air had less carbon dioxide in
it. 2. Scientists believe there are two explanations of why the
ice ages might have occurred. They believe temperatures were
much colder so it never rained, only snowed, or the earth
changed its tilt away from the sun. 3. When the earth began
warming up after the last Ice Age, glaciers were left behind.
Glaciers are sheets of ice that cover rivers and valleys. The
ice would begin to melt and then refreeze. This process went on
for millions of years. 4. About 10,000 years ago, the earth
began to warm up and the ice started to melt. As the ice melted
it left lakes and valleys with a mixture of rocks and soil. The
only ice that was left was up high in the mountains. The
glaciers that exist today ar