Asteroid Aftermath: Stunning Fossils Discovery Details the Day Dinosaurs Were Wiped Out - The Weather Channel

An asteroid impact near what's now the Yucatan Peninsula caused giant waves in an inland sea that sloshed into the mouth of a river, leaving a fossilized record of the day the dinosaurs were wiped off the planet.

(Illustration courtesy of Robert DePalma via UC Berkley)

A site in North Dakota nicknamed Tanis has perfectly preserved fossils of fish, animals and plants.
The fossil layer formed when a killer asteroid struck off what is now the Yucatan Peninsula.
Some of the fossilized fish at the site inhaled tiny glass beads formed by the impact.

Buried for 66 million years, a prehistoric graveyard is revealing what happened in the minutes after a giant asteroid slammed into the Earth and wiped out the dinosaurs, a new study says.

The site, part of the Hell Creek Formation in what is now North Dakota, used to lie along an inland sea that divided North America into two land masses.

“Essentially, what we've got there is the geologic equivalent of high-speed film of the very first moments after the impact,” paleontologist Robert DePalma, the study's lead author, told National Geographic.

Perfectly preserved fossils of fish, animals and plants at the site, which is nicknamed Tanis, offer a detailed recording of what happened immediately after the killer asteroid struck off Mexico's Yucatan Peninsula, according to the study to be published Monday in the Proceedings of the National Academy of Sciences. The impact created a giant crater, called Chicxulub, and it ejected tons and tons of vaporized rock and asteroid dust into the atmosphere. The cloud that enveloped the planet led to the extinction of 75 percent of life on Earth and the end of the Cretaceous period.

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“We’ve understood that bad things happened right after the impact, but nobody’s found this kind of smoking-gun evidence,” study co-author David Burnham of the University of Kansas Biodiversity Institute said in a statement. “People have said, ‘We get that this blast killed the dinosaurs, but why don’t we have dead bodies everywhere?’ Well, now we have bodies. They’re not dinosaurs, but I think those will eventually be found, too.”

Within 45 minutes to an hour, thousands of tiny glass beads formed by the impact began to rain down on the site. Some of these beads, called tektites, were inhaled by the fish in the inland sea, according to a University of California Berkley news release about the study. The tektites would later be found stuck in the fishes' gills. Other tektites, zooming out of the atmosphere at 100 to 200 mph, landed in the mud left by waves from the inland sea. Others are thought to have caused wildfires across the entire continent.

The asteroid's impact also set off shockwaves that caused the inland sea to slosh like water in a bathtub. The waves washed sturgeon, paddlefish and other marine creatures onto a sandbar at the mouth of a river where they were stranded.

Fossilized fish stacked atop each other suggests they were flung ashore and died stranded together on a sand bar after the waves from the inland sea withdrew.

(Courtesy of Robert DePalma via UC Berkley)

The tektites and other debris from the impact fell for another 10 to 20 minutes. Another big wave sloshed out of the sea and covered everything with sand, gravel and fine sediment.

“A tangled mass of freshwater fish, terrestrial vertebrates, trees, branches, logs, marine ammonites and other marine creatures was all packed into this layer by the inland-directed surge,” said DePalma, a University of Kansas doctoral student and a curator at the Palm Beach Museum of Natural History in Florida.

In addition to fish and marine organisms, DePalma, who has worked at the site not far from Bowman, North Dakota, for the past six years, has found parts of a triceratops, a duck-billed hadrosaur, insects, mammals, bones from a marine reptile called a mosasaur, and burned trees and conifer branches. He also found feathers that may have belonged to a dinosaur, according to an extensive article about the find in the New Yorker.

They're all in the sedimentary layer known as the K-T boundary that marks the end of the Cretaceous period and the beginning of the Tertiary period. It's also called the K-Pg boundary.

“This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary,” DePalma said. “At no other K-T boundary section on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day.”

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Mark Richards, a UC Berkeley professor emeritus and professor of earth and space sciences at the University of Washington, said, “It’s like a museum of the end of the Cretaceous in a layer a meter-and-a-half thick."

DePalma said, “It’s difficult not to get choked up and passionate about this topic. We look at moment-by-moment records of one of the most notable impact events in Earth’s history. No other site has a record quite like that. And this particular event is tied directly to all of us — to every mammal on Earth, in fact. Because this is essentially where we inherited the planet. Nothing was the same after that impact. It became a planet of mammals rather than a planet of dinosaurs."

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