About 66 million years ago an asteroid the size of Mount Everest traveling at 45,000 miles per hour hit what is now the Yucatan Peninsula in Mexico. We can’t change the past, but still: what if that asteroid had missed? What would the Earth look like today if dinosaurs were still alive?

Some scientists say that the dinosaurs’ numbers had already been steadily declining for thousands of years before the asteroid hit, so they may have died out on their own without a mass extinction event. Still, the environment might not have suited early mammal populations, and they might not have been able to adapt quickly enough.

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