Ice age

The ice age is a very long period of time when most of the Earth's surface was covered in enormous sheets of ice. It happened many thousands of years ago and lasted for a long time - thousands of years too. During this time, everything got colder and colder, and the ice sheets spread over land in many places. Some animal species had to find new places to live since their old homes were now too cold, or even covered in ice. Eventually, the planet got warmer and the ice melted away, just like it does when you leave an ice cube out in the sun. This time of coldness is called an ice age.