• Ice Age – Period of millions of years where continents were repeatedly glaciated

• Glacial period – time within an ice age where glaciers advanced (grew) more then they retreated (shrank)

• Interglacial period – time within an ice age where glaciers retreated more than they advanced

When did they occur?

As recently as 15,000 years ago, much of N. America was covered in ice during the last ice age.

What are some possible reasons for ice ages?

• Plate Tectonics

• Reduction of CO2 in the atmosphere

• Volcanoes

• Milankovitch Theory

Milankovitch Theory• Ice ages occur in cycles• Milutin Milankovitch (Serbian scientist) proposed

that this regular cycle was the result of three things

Orbit Wobble

How do Scientists Know When Ice Ages Occurred??? - Fossils