The series begins with an exploration of the most violent event in the history of the Earth when, four and half billion years ago, it collided with another planet, Thea. In the second episode, it explores the evidence behind the controversial theory of Snowball Earth - the greatest climate disaster happened 650 million years ago. Then it investigates the Permian extinction, the largest ever when, 250 million years ago, 95% of life was destroyed. The fourth episode explores the trail of clues that lead to what extinguished the dinosaurs 65 million years ago. And finally it maps out key events over the last 75,000 years that had a malign effect on the development of the human race.