An asteriod which fell on the Yucatan peninsula 65 million years ago is credited with wiping out the dinosaurs and many other life forms as part of a huge mass extinction. The cause then was the heavy blanket of particles from the impact that blocked out the sunlight. Now, another mass extinction some 250 million years ago has been linked to global warming caused by volcanic eruptions. Marine species declined by 75 percent while animal and plant species on land declined by 90 percent.
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