-- Triceratops horridus The cause of this disaster was identified decades ago. An asteroid some seven miles across slammed into the Earth, leaving a geologic wound over 50 miles in diameter. In the terrible mass extinction that followed, more than half of known species vanished seemingly overnight. But this worst single day in the history of life on Earth was as critical for us as it was for the dinosaurs, as it allowed for evolutionary opportunities that were closed for the previous 100 million years.
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