Forces of Change
The continents had been uplifted during the previous 15 million years. Rising an average of 600 meters (1,965 ft.), they changed oceanic and atmospheric currents that affect climate.
By two million years ago, much of North America and Eurasia was positioned at high latitudes, far from the equator. In the southern hemisphere, Antarctica was centered on the South Pole.
Changes in the Earth's orbit around the sun cause variations in the amount of solar radiation hitting northern latitudes. During times of reduced radiation, a cooler climate caused snow to persist year-round in Canada.
Glaciers depressed the continental crust as they grew and reshaped the landscape as they moved. A large volume of water was trapped in the ice. Sea levels lowered worldwide, exposing more land. At times, the ice sheet advanced into the Atlantic Ocean, releasing many icebergs that changed ocean currents as they melted.
Read more about these forces in the Museum's Ice Ages Web Exhibit.