America's Ice Age

Why do we have ice ages and when is the next one due? Chart the progress of different ice ages through the history of our planet, from Snowball Earth hundreds of millions of years ago to the recent ice ages. As the Earth circles the sun, its orbit changes slightly and so does it angle of rotation. When the right wobble in our rotation combines with the right orbit, the Earth is, and will again be, plunged into an ice age--but maybe not for a few thousand years.