Climate

Quaternary period:

Temperature dropped, 

Ice sheets spread from the poles, all the way up to Europe and North America and parts 

of Asia and South America,

Sea levels had fallen (too much ice),

When it got warmer the ice melted, creating the Great Lakes.

Tertiary period:

On the beginning of the period, Earth was very warm and moist; tropical, subtropical,

By the middle, earth begun to cool down.