Throughout the history of life on Earth, there have been at least six major mass extinctions. The one that killed off the dinosaurs occurred about 65 million years ago, and it is thought to have been the result of the impact of a large asteroid. The largest mass extinction of them all, however, was the Ordovican mass extinction, which occurred about 450 million years ago. The cause of this mass extinction is uncertain, but scientists have recently demonstrated how this extinction may have been initiated by an intense burst of gamma rays produced by the explosion of a nearby star. A burst as short as 10 s could have led to the loss of Earth's protective ozone layer, thereby exposing life on Earth to dangerous ultraviolet rays from our Sun. The probability of another nearby star exploding soon is quite low. But take a look around you.Scientists point to the sixth mass extinction as occurring right now. Discuss possible causes of this mass extinction.How long might this mass extinction take? What creatures might survive? Should humans do anything to minimize this mass extinction, or should we just accept it as a natural course of Earth's history? Throughout the history of life on Earth, there have been at least six major mass extinctions. The one that killed off the dinosaurs occurred about 65 million years ago, and it is thought to have been the result of the impact of a large asteroid. The largest mass extinction of them all, however, was the Ordovican mass extinction, which occurred about 450 million years ago. The cause of this mass extinction is uncertain, but scientists have recently demonstrated how this extinction may have been initiated by an intense burst of gamma rays produced by the explosion of a nearby star. A burst as short as 10 s could have led to the loss of Earth's protective ozone layer, thereby exposing life on Earth to dangerous ultraviolet rays from our Sun. The probability of another nearby star exploding soon is quite low. But take a look around you. Scientists point to the sixth mass extinction as occurring right now. Discuss possible causes of this mass extinction. How long might this mass extinction take? What creatures might survive? Should humans do anything to minimize this mass extinction, or should we just accept it as a natural course of Earth's history? Throughout the history of life on Earth, there have been at least six major mass extinctions. The one that killed off the dinosaurs occurred about 65 million years ago, and it is thought to have been the result of the impact of a large asteroid. The largest mass extinction of them all, however, was the Ordovican mass extinction, which occurred about 450 million years ago. The cause of this mass extinction is uncertain, but scientists have recently  demonstrated how this extinction may have been initiated by an intense burst of gamma rays produced by the explosion of a nearby star. A burst as short as 10 s could have led to the loss of Earth's protective ozone layer, thereby exposing life on Earth to dangerous ultraviolet rays from our Sun. The probability of another nearby star exploding soon is quite low. But take a look around you. Scientists point to the sixth mass extinction as occurring right now. Discuss possible causes of this mass extinction. How long might this mass extinction take? What creatures might survive? Should humans do anything to minimize this mass extinction, or should we just accept it as a natural course of Earth's history?