An ice age is a period of long-term reduction in the temperature of the Earth's surface and atmosphere,resulting in an expansion of continental ice sheets,polar ice sheets and alpine glaciers.Glaciologically,ice age is often used to mean a period of ice sheets in the northern and southern hemispheres.More colloquially,when speaking of the last few million years,ice age is used to refer to colder periods with extensive ice sheets over the North American and Eurasian continents:in this sense,the most recent ice age peaked about 11,000 years ago.
