SUMMARY: Most paleontologist believe that a gigantic asteroid struck Mexico 65 million years ago and killed all the dinosaurs; end of story. But a minority believe that the Earth's environment was already uncomfortable for dinosaurs because of a series of asteroid strikes and volcano eruptions - the asteroid was just the straw that broke the camel's back. By studying the life spans of colonies of one-celled organisms, paleontologist Gerta Keller has uncovered that the Cretaceous period might have lasted 300,000 years after the asteroid impact.


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