“In the history of life on Earth, we know of five different mass extinctions when a majority of life on Earth at the time disappeared in the blink of a geologic eye,” says biologist and science writer Joe Hanson. The most cited is the Cretaceous-Paleogene Extinction 66 million years ago that wiped out the dinosaurs. But the most deadly was the mother of all extinctions called the End Permian, 250 million years ago, which obliterated 96 percent of Earth’s species. Hanson says we are now in the midst of the sixth mass extinction and we are the perpetrators. Hanson explains why in this edition of It’s OK To Be Smart.