Direct fossil evidence of the cataclysmic meteor impact that led to the extinction of the dinosaurs 66 million years ago has been found.
The last hours of the Cretaceous Period.
The actual paper in the Proceedings of the National Academy of Sciences USA won’t come out until Monday, but the media was allowed to see it and report on it in advance, and luckily Attorney General William Barr wasn’t the one doing the summary.
I’ve read several intros on this, but the one at UC Berkeley’s news site, I think, does the best job of setting the stage, and you should go read that whole article:
The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota.
Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills.
The heaving sea turned into a 30-foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud. The torrent of rocks, like fine sand, and small glass beads continued for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand and fine sediment, sealing them from the world for 66 million years.
This unique, fossilized graveyard — fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates and snail-like marine cephalopods called ammonites — was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota. The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 — that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth.
Just so you understand the significance of the find, let’s see what some experts have to say about it. There’s this:
“You’re going back to the day that the dinosaurs died,” said Timothy Bralower, a Pennsylvania State University paleoceanographer who is studying the impact crater and was not involved with this work. “That’s what this is. This is the day the dinosaurs died.”
Or this:
Other researchers were impressed by the work. “When I first read it, I kept saying ‘wow, wow, wow,’” H. Jay Melosh, distinguished professor of Earth, atmospheric, and planetary science at Purdue University, told Gizmodo. “I think this is one of the most spectacular paleontological discoveries of the century. It’s a snapshot of the moment at which major deaths were occurring right after the impact.”
Or this:
“Just the idea of fish with impact particles stuck in their gills from 66 million years ago, and trees with amber with impact particles, it’s so extraordinary that you do a double take for sure,” said Matthew Lamanna, a vertebrate paleontologist at the Carnegie Museum of Natural History in Pittsburgh, who was not involved with the research.
The study’s authors weren’t too bashful, either:
“We’ve understood that bad things happened right after the impact, but nobody’s found this kind of smoking-gun evidence,” said David Burnham, a study co-author and geologist at the University of Kansas 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.”
We can identify the K-T boundary by its unusual concentration of iridium:
What is the K-T boundary? K is actually the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period. So the K-T boundary is the point in between the Cretaceous and Tertiary periods. Geologists have dated this period to about 65.5 million years ago.
When physicist Luis Alvarez and geologist Walter Alvarez studied the K-T boundary around the world, they found that it had a much higher concentration of iridium than normal – between 30-130 times the amount of iridium you would expect. Iridium is rare on Earth because it sank down into the center of the planet as it formed, but iridium can still be found in large concentrations in asteroids. When they compared the concentrations of iridium in the K-T boundary, they found it matched the levels found in meteorites.
The researchers were even able to estimate what kind of asteroid must have impacted the Earth 65.5 million years ago to throw up such a consistent layer of debris around the entire planet. They estimated that the impactor must have been about 10 km in diameter, and release the energy equivalent of 100 trillion tons of TNT.
This is all pretty awesome for Walter Alvarez, because he got to go to the North Dakota site and help in the discovery phase that gave direct evidence for his own theory.
This site dates to right on that K-T boundary:
This is what makes the new research, led by Robert DePalma at the University of Kansas, so exciting—the description of a pair of sediment layers at the Tanis site of the The Hell Creek Formation in southwestern North Dakota. Both layers contain an excess of iridium, but only the lower level contains glass pieces that seemed to have been deposited from an inland-moving force. They take this to mean that they’re observing two events: The upper layer is the settling dust from after the impact. The lower is a large deposit of sediment from the hours following the impact.
DePalma is a 37-year-old graduate student at the University of Kansas who has been secretly excavating this site for about six years. I know how exciting and addictive this can be. My family was in Florissant, Colorado in 2017 (on our eclipse trip), and we found, in 3 days of picking apart quarry shale, some very cool sequoia and winged ant fossils that I wrote about before.
If you have any doubt that a meteor impact near the Yucatan Peninsula could cause such devastation in North Dakota, keep in mind that in 2010, a magnitude 9.0 earthquake in Japan (a mere pittance compared to a 10-km meteor impact, which would have up to 100 times the seismic effects) caused standing waves several feet high in fjords in NORWAY.
I’ll let DePalma sum all of this up:
“This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary,” said DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas. “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.”
I suspect he'll successfully complete his Ph.D. 😁