Ice age
An ice age is a period of time when decreased temperature of Earth's surface and atmosphere results in the prolonged presence or expansion of continental alpine glaciers and polar ice caps. The term is applied in several different senses to very long and comparatively short periods of cooling. An ice age may consist of numerous sub-periods where the global temperature and glaciation fluctuates, with the colder periods called glacials, and relatively warmer periods called interglacials.
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