Ancient Earth: Permian (Final)
Some of the most wondrous creatures in the history of our planet roamed on land and thrived at sea during the Permian period. Among them were the first saber-toothed carnivore and a 40-foot shark with a circular saw for a mouth. But something terrible happened 252 million years ago, when our world suffered the worst of five major mass extinctions. Just recently, scientists think they have finally identified the smoking gun that nearly wiped out all life on Earth.