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Eyebrow-raising extinction study goes public, but co-author says it’s just the start

Alan Boyle
Geophysicists Walter Alvarez (at left) and Mark Richards (background) examine a piece of impact ejecta at the North Dakota fossil site. (Jackson Leibach Photo via University of Kansas)

After days of puzzling over secondhand reports, anyone with an internet connection can now read a research paper about a fossil graveyard in North Dakota that appears to document the day nearly 66 million years ago when an asteroid pushed the dinosaurs and many other species into extinction.

Even scientists who criticized the way the news about the site came out on Friday acknowledged that the discovery, as described in the Proceedings of the National Academy of Sciences, was astounding.

“I am very much looking forward to the crowd-sourced opinions of everyone,” University of Edinburgh paleontologist Steve Brusatte said in a tweet. “There is a real thrill and a real mystery around this discovery, and it is EXCITING! Let’s see where the evidence leads.”

The study documents fossil evidence for a catastrophic fish kill that did in many other organisms as well. Intermixed with the fossilized remains were tiny beads of glass that had turned to clay. Some of those beads were found embedded in the gills of the fish.

The evidence led the research team, headed by paleontologist Robert DePalma, to conclude that the Cretaceous creatures were washed up onto a sandbar by a giant wave of water. Then they were pelted by hot droplets of molten rock, known as tektites, which were thrown up into the stratosphere by an asteroid impact thousands of miles away.

In the paper, the research team lays out a scenario suggesting that the impact produced a magnitude 10 to 11 earthquake, which sparked a standing wave in the body of water where the fish had lived. Such a wave, known more scientifically as a seiche (pronounced like “saysh”), could have done as much damage as a tsunami within an hour after the asteroid hit. That scenario would leave enough time for the tektites to deliver the coup de grace.

One of the study authors who came up with that scenario is Mark Richards, a geophysicist who left the University of California at Berkeley last July to become the University of Washington’s provost and executive vice president for academic affairs.

Today, Richards said the seiche scenario isn’t the only possibility for explaining what happened in North Dakota during what’s known as the Cretaceous-Paleogene or Cretaceous-Tertiary extinction.

“I think that the surge, unless it was some freak coincidence with something else, was likely seismically induced,” Richards told GeekWire. “Now, it could have been from a seiche. Also, for example, you could have had a local landslide that was triggered by seismic waves. We have to be pretty cautious.”

Researchers Jan Smit, Robert DePalma, Walter Alvarez and David Burnham collect a box core sample of the Cretaceous-Paleogene boundary layer at the Tanis site in North Dakota. (Jackson Leibach Photo via University of Kansas)

A leading theme of the criticism on Friday had to do with the way DePalma’s findings were portrayed in a detailed report published by The New Yorker. Some felt that DePalma was portrayed as an incautious, publicity-grabbing Indiana Jones wannabe, dwelling on the dinosaur angle and talking up finds that didn’t end up being mentioned in the peer-reviewed paper.

Richards, however, said he’s had “nothing but good relations with Robert.” DePalma is still working on his Ph.D. at University of Kansas, but has been doing field work for years and currently serves as a curator of paleontology at the Palm Beach Museum of Natural History in Florida.

“I’ve found him to be very spirited, very generous,” Richards said. “Obviously, it’s somewhat unusual for somebody who hasn’t received their Ph.D. to be thrust into the limelight like this, but let’s keep the story about the science.”

Richards suspects that the newly published findings “will make a lot of people more attracted” to the killer-asteroid hypothesis as an explanation for the dinosaurs’ doom. One of Richards’ co-authors, Berkeley geologist Walter Alvarez, laid out that explanation nearly 40 years ago in league with his Nobel-winning father, Luis Alvarez. But Richards — and Walter Alvarez, for that matter — don’t rule out the possibility that other factors, such as an upswing in volcanic eruptions, could have played a part.

Now that the paper is out, Richards suspects that other scientists will take a closer look at the more than 200 other sites around the world that show the signs of the Cretaceous-Paleogene boundary. “At least two of those of which I’m aware involve deposits have been interpreted as being tsunamis,” Richards said.

“If you take Robert’s paper and findings at face value, this is a truly sensational finding from a paleontological standpoint,” he said. “My guess is that people are going to go all over the world looking for things that are similar. To which I would say, ‘Good luck.’ Obviously this is a pretty unique circumstance.”

Bottom line? Richards says paleontologists, and the people who follow their work, “really need to keep a pretty strong sense of humility at this point.”

“This is apparently a really significant discovery — and yet I’m guessing that five years from now, we’re going to be seeing things at this particular site, and perhaps at other sites, that are going to go far beyond what we understand right now,” he said. “I would say this is the beginning of a process, and certainly not the end.”

In addition to DePalma, Richards and Alvarez, the authors of the PNAS paper, “A Seismically Induced Onshore Surge Deposit at the KPg Boundary, North Dakota,” include Jan Smit, David Burnham, Klaudia Kuiper, Phillip Manning, Anton Oleinik, Peter Larson, Florentin Maurrasse, Johan Vellekoop and Loren Gurche.

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