What is an ice age?
An ice age is a relatively cool period in Earth history, when vast ice sheets cover much of Earth’s land surface. There have been at least five major ice ages during the last billion years. The most recent ice age began 2.5 million years ago.


How do we know that ice ages occurred?
The giant ice sheets that form during ice ages leave behind geological evidence in the surrounding landscape. Evidence for ice ages can also be found by studying natural recorders of climate change, such as fossil pollen, ancient coral reefs, ocean sediments and ice cores


What causes an ice age?

This question can actually be broken down into two separate questions:

1) W hat causes the long-term changes leading to an ice age?
Factors that are thought to play important roles in long-term changes in Earth's climate over millions or tens of millions of years are

    • Changes in the positions of the continents
    • Variations in the energy output of the sun
    • Changes in atmospheric carbon dioxide concentration
    • Changes in volcanic activity
    • Influence of the biosphere

2) What causes the glacial cycles within an ice age?

During an ice age, the shorter-term cycles of advancing and retreating glaciers are thought to be driven by regular, predictable variations in Earth's orbit and orientation relative to the Sun.