A massive asteroid struck Earth 66 million years ago and profoundly changed our planet. More than three-quarters of plant and animal species went extinct. When the world finally recovered, the only dinosaurs left were birds. Mammals took over most of the roles dinosaurs once filled.
Without that catastrophe, humans wouldn’t be here today. But it also took many other changes to produce the world we now live in. Major shifts in climate, land, and oceans unfolded over tens of millions of years. A warm greenhouse environment, with high levels of gases like carbon dioxide in the atmosphere, became a cooler, drier, icehouse world.
