3. Late Cretaceous, 100 million to 66 million years ago

Boom! You saw this one coming, right? As the story goes, Tyrannosaurus rex, ankylosaurs, pterosaurs the size of planes, and all the other Cretaceous creatures were minding their own business when a huge asteroid collided with Earth. The non-avian dinosaurs were done. On the bright side, it gave mammals an opportunity to flourish and begin their own heyday on the planet. The Late Cretaceous was truly a pivotal moment in Earth’s evolutionary history, and humans would not exist without the mass extinction of 66 million years ago.