The asteroid that ended the dinosaurs

Chicxulub, 66 million years ago: a 10 km asteroid, a crater 180 km wide, a world gone dark, and how we now watch for the next one

Watch it in 3D

Step by step

Into a shallow sea

The asteroid did not stop at the sea floor. The water there was shallow, and below it lay kilometres of limestone and gypsum, rich in carbon and sulfur. In a fraction of a second the asteroid and a far greater mass of that rock turned to vapour and melt. Because the rock was so rich in sulfur, the impact threw an enormous amount of it into the sky, which would matter most of all.

A crater 180 km wide

In a large impact the ground behaves for a few minutes almost like a liquid. The blast dug a bowl many kilometres deep; its floor sprang back up, overshot and collapsed outward, leaving a ring of peaks inside the rim. Computer models say this took about ten minutes. The crater is buried today under hundreds of metres of younger limestone, partly under land and partly under the sea.

In 2016 IODP-ICDP Expedition 364 drilled into the peak ring from a platform off the coast and brought up core from about 506 to 1,335 m below the sea floor. In the peak ring it found granite, shocked and fractured, that normally lies kilometres down in the crust: deep rock thrown upward in minutes (Morgan et al., 2016).

Fire in the sky, waves at sea

Vapour and melt shot up out of the crater, some of it beyond the atmosphere. Over the following hours billions of tonnes of small glassy beads fell back all over the world. Some models find that their fall heated the air enough to set forests alight far from the crater; others find the falling dust shielded the ground. Soot in the boundary clay shows that much did burn.

The long dark winter

About three quarters of the species of plants and animals vanished, among them every dinosaur except the birds, the pterosaurs, the great marine reptiles and the ammonites. Survivors were mostly small: animals that could burrow, live in water, or eat seeds, roots and dead things. The cold did not last; once the dust and sulfur fell out, the carbon dioxide kept the world warmer for about 100,000 years (MacLeod et al., 2018).

The clues in the rocks

The proof is a thin layer of clay found worldwide where the age of the dinosaurs ends, full of iridium, shocked quartz and glassy beads, and a crater buried under Yucatán.

At Tanis, in North Dakota, a river deposit holds fish with impact beads in their gills, buried by a surge of water within hours of the impact (DePalma et al., 2019). Earth here is drawn with today's continents, though 66 million years ago they lay a little differently.

The mammals' turn

At Corral Bluffs in Colorado, fossils from the first million years after the impact show the recovery (Lyson et al., 2019). Within about 100,000 years the number of mammal species had roughly doubled, and within 300,000 years the largest mammals were about three times heavier. By about 700,000 years some were the size of wolves. Plants came back with them: ferns first, then palms, then the first legumes.

Birds, the only dinosaurs that survived, spread into the empty spaces too. The earliest primates, our own branch, appear in rocks laid down within about a million years of the impact. Whether mammals would have risen without the asteroid, no one can know; what is certain is that they did after it.