Climate Has Varied Drastically in Earth History

The story of Earth’s climate has been a story of massive changes. Earth has been much warmer and much colder than it is today, including times when there were no ice caps and times when the entire planet was nearly frozen over.

Earth during a time when there were no polar ice caps. — **No Ice Caps**

Earth during a time when it was largely covered in ice. — **Nearly Frozen Over**

These changes occur because the chemical composition of the atmosphere has changed over time, varying the strength of the greenhouse effect, and also because the amount of solar radiation has varied over time.