Biology

Fossil site is first ever to show deaths from mass extinction asteroid impact

A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a dinosaur, the first victims of Earth’s last mass extinction event
A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a dinosaur, the first victims of Earth’s last mass extinction event
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Walter Alvarez and Robert DePalma at the Tanis outcrop in North Dakota
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Walter Alvarez and Robert DePalma at the Tanis outcrop in North Dakota
Tektites recovered from the Tanis fossil bed
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Tektites recovered from the Tanis fossil bed
Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the seiche withdrew
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Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the seiche withdrew
A perfectly preserved fish tail from Tanis deposit
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A perfectly preserved fish tail from Tanis deposit
A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a dinosaur, the first victims of Earth’s last mass extinction event
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A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects and a dinosaur, the first victims of Earth’s last mass extinction event
Fish carcasses and two logs tossed together by the seiche created by seismic waves from the meteor impact
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Fish carcasses and two logs tossed together by the seiche created by seismic waves from the meteor impact
Jan Smit, Mark Richards and Walter Alvarez at the North Dakota site of dinosaur-killing meteor’s first victims
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Jan Smit, Mark Richards and Walter Alvarez at the North Dakota site of dinosaur-killing meteor’s first victims

A dramatic find in North Dakota has uncovered the first known victims of the asteroid impact that led to the extinction of the dinosaurs 66 million years ago. An international team of paleontologists and geologists has found a massive collection of fossils of fish and other animal that were killed by a seismic sea wave and a shower of burning glass beads less than an hour after the asteroid strike off the shore of what is now Yucatan.

The mass extinction event caused by the impact of an asteroid or perhaps a comet at the end of the Cretaceous age that wiped out 75 percent of life on Earth is widely accepted, but for most people, it has a strangely abstract quality.

It's easy to accept the idea of a giant object hitting the ocean, the massive shock waves and tsunamis and followed, as well as the concept of the sun being blotted out for years afterward, killing off plants and animals in a massive ecological chain of events. But much of it remains very clinical. It involves an ancient meteor crater on the Caribbean seabed, a sudden jump in iridium in the stratigraphy brought by the asteroid that created what is called the K-T boundary in the geological record, and an equally sudden disappearance of the dinosaurs, which had reined supreme on Earth for tens of millions of years.

Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the seiche withdrew
Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the seiche withdrew

It's all very convincing, but what happened at the time of impact? What was it like being in a place where a planet-wide catastrophe took place? It turns out, it wasn't very pleasant.

Thousands of miles away from Mexico, North Dakota may seem like an odd place to find evidence of the Yucatan, or Cretaceous–Tertiary (K–T) extinction event, but 66 million years ago it was part of a massive inland sea called the Westland Interior Seaway. One spot near Bowman, North Dakota, called Tanis by the geologists, was the mouth of a freshwater river teeming with sturgeon and paddlefish while triceratops and duck-billed hadrosaurs roamed the banks.

That all changed in an instant when the asteroid strike happened. According to a team led by Robert DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas, the fossil record uncovered at Tanis indicates a disaster like something out of the Old Testament.

Fish carcasses and two logs tossed together by the seiche created by seismic waves from the meteor impact
Fish carcasses and two logs tossed together by the seiche created by seismic waves from the meteor impact

The asteroid strike took place some 3,000 km (1.865 mi) away and a conventional tsunami would have taken up to 12 hours to reach Tanis – if it didn't die down first. Instead, the team argues that a seismic wave hit 10 minutes after impact with the force of a 10 or 11 magnitude earthquake, generating a standing wave or seiche that created a sloshing wall of water at the mouth of the river 30 ft (10 m) high that reversed the flow of the river and threw fish and other water life onto a sandbar, later to be buried by successive waves of mud and debris.

Meanwhile, the initial Yucatan blast vaporized the asteroid and hurled millions of tonnes of debris into the atmosphere. The superhot remains of the asteroid cooled into burning hot beads of glass called tektites that were about one to five millimeters in diameter.

In about 45 minutes, these rained down on the fish at Tanis at up to 200 mph (322 km/h), filling their mouths and gills. Others left pits in the uncovered mud and those that touched land started fires as they came down in a fiery torrent that lasted for up to 20 minutes. Some landed in resin and were preserved as it turned into amber. It was a scene that must have been common around the planet, but the first evidence is at Tanis.

Tektites recovered from the Tanis fossil bed
Tektites recovered from the Tanis fossil bed

"This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary," says DePalma. "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.

"Tsunamis from the Chicxulub impact are certainly well-documented, but no one knew how far something like that would go into an inland sea. When [Mark Richards, professor of earth and space sciences at the University of Washington] came aboard, he discovered a remarkable artifact – that the incoming seismic waves from the impact site would have arrived at just about the same time as the atmospheric travel time of the ejecta. That was our big breakthrough."

The research will be published in the Proceedings of the National Academy of Sciences.

The video below shows Robert DePalma excavating at the Tanis fossil site in North Dakota.

Source: UC Berkeley

Stunning discovery offers glimpse of minutes following ‘dinosaur-killer’ Chicxulub impact

4 comments
SK Banerjee
Is there any reliable record if earth's rotation about its own axis or around Sun was affected due to this impact ?
MarylandUSA
I was born in 1956. This discovery ranks as one of the 10 most significant discoveries of my lifetime, along with the discovery or verification of the cosmic microwave background, plate tectonics, neutron stars, quantum entanglement, and homo sapiens' interbreeding with Neanderthals and Denisovans.
Thinker
Amazing! All that conjecture based on the finding of a bunch of fossils and glass beads, thousands of miles from the main event no less. Is there no one in the world that is able or willing to challenge all this information?
Gregg Eshelman
Now paleontologists have a definite radius from the impact site to search for more places like this. Other articles have mentioned that some paleontologists are questioning the validity of the find (sounds like sour grapes to me), making complaining noises about how DePalma has yet to get his PhD, and questioning his competency because of one incident years ago when he accidentally included a turtle bone in a reconstruction of a newly discovered raptor species. Then there's the beef some of them have with the site being on private land and the deal DePalma has made with the land owner for controlling access and that DePalma gets to be the man in charge. Some of that stems from when DePalma was in high school and loaned many of his fossils (he started collecting when he was 9 years old) to a museum. When the museum closed they conveniently had "lost" any documentation that the fossils were his. He's not wanting to get screwed over again by museums and other paleontologists. Remember how they tried to take Sue the T-Rex away from the person whose land it was found on? He had to sue to be allowed to sell his own property the government tried to claim.