Ice age is a period in Earth's history when ice sheets cover vast regions of land. Ice ages alternate with interglacial periods, when the ice sheets mostly disappear. An ice age generally lasts about 100,000 years; an interglacial period, from 10,000 to 20,000 years. The most recent ice age ended about 11,500 years ago. Most earth scientists expect that another ice age will follow the interglacial period in which we now live.