Georges Cuvier, working in the early 19th century, was one of the first paleontologists. He believed that geological catastrophes, or "revolutions", drove waves of sudden extinction. In part, his ideas were formed by study of a giant sea lizard, Mosasaurus, that lived and went extinct at the end of the Cretaceous.

Charles Darwin saw the end of the Cretaceous rather differently. He thought extinctions happened gradually, driven by everyday processes working over many millions of years, just as sedimentation and erosion slowly reshaped the land.

The debate continued for over a century, but the idea of catastrophic extinction gained ground as paleontologists collected more fossil species, timing species' appearances and disappearances. Massive numbers of species disappeared near the end of the Cretaceous, rapidly, around the world, both on land and in the sea. These severe, rapid, worldwide extinctions implied a severe, worldwide, rapid cause—a catastrophe.

Finally, in 1980 physicist Luis Alvarez identified a possible driver of the extinctions—a giant asteroid impact, later traced back to an enormous crater beneath the town of Chicxulub, in Mexico. Debris shot into the upper atmosphere by the impact blocked out the sun, causing photosynthesis to stop, and temperatures to plunge.