ice ages

Periods in the Earth's history when ice-sheets and glaciers advance to cover areas previously not affected by ice. There is evidence of at least six Ice Ages having occurred throughout the Earth's history, the earliest dating back to 2.3 billion years ago. The best known is the most recent Ice Age, which began c.2 million years ago and lasted until the retreat of the ice to its present extent c.10,000 years ago. The present time may be a warmer period known as an interglacial. The last Ice Age produced many of the landforms seen in northern continents and affected sea level on a global scale.

World Encyclopedia. Philip's, 2005.