PBS Eons has a new episode. This one is about Snowball Earth, which is the theory that the whole earth was covered by ice. This happened at least twice in the last 700 million years.
Over 600 million years ago, sheets of ice coated our planet on both land and sea. How did this happen? And most importantly for us, why did the planet eventually thaw again? The evidence for Snowball Earth is written on every continent today.
