What is an Ice Age?

Hi, I’m Emerald Robinson. In this “What Is” video we’re going to take a closer look at ice ages.

In 1840, Swiss scientist Louis Agassiz noticed glaciers–huge rivers of ice created by snowfall–occurred throughout northern Europe. As glaciers move they transport rocks and scour the ground beneath them, leaving evidence of their passing. Agassiz theorized glaciers were the remnants of a huge glacial ice field that once covered much of the continent. Geologic evidence of massive glacial activity also occurs in North America.

Agassiz had discovered evidence of the last ice age, a period of time when glacial ice fields extended across large sections of the planet. Geologists have evidence of three ice ages–more properly called glacial ages. The oldest occurred 275 million years ago. The second, which affected parts of Africa, India and Australia, occurred 275 million years ago.

The last glacial age, and the only one to occur since humans appeared, began 1.5 million years ago, and receded 15,000 years ago. During that time the Laurentide ice field covered all of Canada and extended as far south as Indiana.

Glacial ages have enormous effects on the plant’s weather patterns, animals and plant life. Animals that cannot adapt to the colder environments die out. Similarly, animals that adapt to cold environments may not survive the change when glaciers recede.

The Milankovich theory, by astronomer Milutin Milankovich, suggests variations in the earth’s orbit account for glacial ages. Instead of orbiting the sun in a constant pattern, the earth “wobbles.” Over millions of years this “wobbling” affects global temperatures. As glacial ice fields spread, snow and ice reflect sunlight that would otherwise warm the earth, causing further drops in cold temperatures. Low levels of carbon dioxide in the atmosphere can also contribute to a glacial age.