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These 10 unsolved mysteries still don’t let scientists sleep at night. And you will probably lose sleep over it, too!
Mass extinction of 90 percent of species on Earth. 252 million years ago, about 90 percent of species were wiped off the face of the earth. Scientists suspect volcanos and asteroids are to blame, but there are also those who think the true culprit can only be seen through a microscope.
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