An ice age is a period of long-term reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. read more
During the Ice Age, the Earth's average temperature was about 12 degrees Fahrenheit colder than it is today. That was enough to keep snow from melting during the summers in northern regions. As snow fell on snow, thick sheets of ice called glaciers formed. read more