Climate Change

Scientists use geologic evidence to study how the Earth’s climate has changed over time. The Earth has experienced several ice ages, which are periods of cooling that last thousands of years.

The most recent ice age occurred about two million years ago. Throughout an ice age there are episodes called glacial and interglacial periods. Glacial periods experience global cooling and massive ice sheets develop and move south. Interglacial periods experience global warming and the edges of glaciers melt and retreat.

Theories that attempt to explain the occurrence of ice ages include the Earth’s changing motion, continental movement due to plate tectonics, volcanic ash in the atmosphere, and the impact of an asteroid hitting the Earth’s surface. A combination of these theories may have influenced climate change over geologic time.