What year did the ice age begin?
While an ice sheet on Antarctica began to grow some 20 million years ago. During the late Pliocene the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacials (glacial advance) and interglacials (glacial retreat). The earth is currently in an interglacial, and the last glacial period ended about 10,000 years ago.
