Throughout the history of life on Earth, there have beenat

Chapter 17, Problem 82

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Throughout the history of life on Earth, there have beenat least six major mass extinctions. The one that killedoff the dinosaurs occurred about 65 million years ago,and it is thought to have been the result of the impactof a large asteroid. The largest mass extinction of themall, however, was the Ordovican mass extinction, whichoccurred about 450 million years ago. The cause of thismass extinction is uncertain, but scientists have recently demonstrated how this extinction may have been initiatedby an intense burst of gamma rays produced by theexplosion of a nearby star. A burst as short as 10 s couldhave led to the loss of Earths protective ozone layer,thereby exposing life on Earth to dangerous ultravioletrays from our Sun. The probability of another nearby starexploding soon is quite low. But take a look around you.Scientists point to the sixth mass extinction as occurringright now. Discuss possible causes of this mass extinction.How long might this mass extinction take? Whatcreatures might survive? Should humans do anything tominimize this mass extinction, or should we just accept itas a natural course of Earths history?

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