THE DAY THE CRETACEOUS ENDED

When the asteroid hit, it sent Cret trillions of tons of molten rock and dust into the atmosphere, much of it hotter than the surface of the sun.

- Jeanne Miller

One day about 66 million years ago, life on our planet changed forever. It happened when an asteroid the size of a mountain tore through the atmosphere and slammed into the Yucatán Peninsula. The collision set off a series of events that killed 75 percent of all animal and plant species, including dinosaurs. Thus ended the Cretaceous geologic period.

Fiery debris from the cataclysm set forests within thousands of miles ablaze. Liquefied rock formed tiny blobs of glass that blasted outward from the site and shot through the atmosphere. Meanwhile, a gigantic earthquake caused by the impact propelled seismic waves through the Earth’s crust, sending water sloshing onto land.

Far Away in North Dakota

Paleontologist Robert DePalma believes he has found evidence of the first minutes to hours of that catastrophic event. But it’s not at the asteroid’s crash site. It’s at a North Dakota cattle ranch, some 2,000 miles (3,220 km) away.

Even as a child, DePalma wondered what the Cretaceous was like. He was fascinated by bones and how they worked together. By age 6 or 7 he was finding fossilized bones from mammals in central Florida. And at age 9 he found his first dinosaur bone on a family trip to Colorado.

In 2004, as a student at the University of Kansas, DePalma excavated layers of an ancient pond in the Hell Creek Formation, a geological region that extends across parts of Montana, Wyoming, North Dakota, and South Dakota. The exposed rock bears fossils from the late Cretaceous. DePalma’s advisor suggested he look for a site close to the dividing line between the Cretaceous Period and the Paleogene Period, which followed. Geologists call the line that separates those two periods the K-Pg boundary.