This series is based on the big 5 mass extinctions, a smaller one 74,000 years ago, and a future one. The 1st one, "Death Rays" took place in the Ordovician 450 million years ago caused by a gamma ray burst. The 2nd one, "Hell on Earth", took place in the Devonian Period 377 million years ago, which was caused by a super plume volcanic eruption. The 3rd and 4th episodes "Doomsday" and "Panic in the Sky" are about the K-T Extinction, or the death of the dinosaurs by a massive asteroid 6-miles wide. The 5th one "The Great Dying" is about the Permian by a massive volcanic eruption in Siberia 250 million years ago and was the worst one yet. The 6th one during the Triassic Period "Strangled" 200 million years ago was also caused by a massive volcanic province like the Permian one. The 7th one "Fire and Ice" took place 74,000 years ago during the Pleistocene epoch and was caused by a Supervolcano Toba in Sumatra, Indonesia and killed the giant mammals of SE Asia. The last one the 8th episode "The Next Extinction" is about an asteroid hitting New York City.
That was the episode guide, I hope this review helped you?