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Fish fossils and triceratops skin are displayed during a display at the Goddard Space Flight Center in Greenbelt, Md., on Wednesday, April 6, 2022. (Kenneth Chang/The New York Times)
GREENBELT, Maryland — Perfectly intact remains of the asteroid that wiped out the dinosaurs have been discovered, say scientists studying a site in North Dakota that is a time capsule from that calamitous day 66 million years ago.
Scientists believe that the object that hit the Yucatán Peninsula, in what is now Mexico, was regarding 10 kilometers wide, but there has been a debate to identify what exactly it was. Was it an asteroid or a comet? If it was an asteroid, what kind was it: a solid, metallic one, or a bunch of rocks and dust held together by gravity?
“If we can identify it, and we’re on track to do so, then we can say, ‘Amazing, we know what it was,'” Robert DePalma, a paleontologist leading the excavation of the site, said Wednesday during a talk at the Goddard Space Flight Center. of NASA in Greenbelt.
A video of the talk and subsequent discussion between DePalma and leading NASA scientists will be posted online in a week or two, a Goddard spokesman said. Many of these discoveries will be covered in “Dinosaurs: The Final Day”, a BBC documentary narrated by David Attenborough, due to air in the UK this month. In the United States, “Nova,” a PBS program, will air a version of the documentary next month.
An article in The New Yorker magazine from 2019 described the site in southwestern North Dakota, called Tanis, as a prodigious place full of fossils that were buried following the impact that occurred some 3,000 kilometers away. Many paleontologists were intrigued, but they weren’t sure how far-reaching DePalma’s claims were; a research paper published that year by DePalma and his collaborators described above all the geological environment of the site, which once stood on the banks of a river.
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Robert DePalma, a paleontologist, gives a presentation on his finds of fossil remains, at the Goddard Space Flight Center in Greenbelt, Md., on Wednesday, April 6, 2022. (Taylor Mickal/NASA via The New York Times)
The object’s collision with Earth created a crater regarding 100 miles wide and nearly 18 miles deep, and the molten rock that was blown into the air cooled and formed glass spherules, one of the hallmarks left by meteorite impacts. In the 2019 paper, DePalma and her colleagues described how spherules raining from the sky clogged the gills of paddlefish and sturgeons, ultimately suffocating them.
Normally, the minerals on the outside of the spherules produced by the impact undergo transformations over millions of years of chemical reactions with water. But in Tanis, some of these landed on tree resin, providing them with a protective enclosure of amber and keeping them almost as pristine as the day they formed.
In the latest findings, which have yet to be published in a peer-reviewed scientific journal, DePalma and his research colleagues focused on unmelted bits of rock that are inside glass.
“All these little dirty nuggets out there, every single speck that obscures this beautiful clear glass, is a piece of debris,” said DePalma, a graduate student at the University of Manchester, England, and an associate professor at Atlantic University. from Florida.
He said finding amber-encased spherules is like sending someone back in time to the day of the impact, “collecting a sample, bottling it, and preserving it for today’s scientists.”
Most of the rock chunks contain high levels of strontium and calcium, indicating that they were part of the limestone crust where the meteor impacted.
However, the composition of the fragments present in two of the spherules was “extremely different,” DePalma said.
“They were not enriched with calcium and strontium, as we would have expected,” he explained.
Instead, they contained higher levels of elements like iron, chromium, and nickel. That mineral composition points to the presence of an asteroid, and in particular a type known as carbonaceous chondrites.
“Seeing a piece of the culprit is a goosebump-raising experience,” DePalma said.
The finding supports a discovery reported in 1998 by Frank Kyte, a geochemist at the University of California, Los Angeles. Kyte said he had found a fragment of the meteorite in a core sample drilled off Hawaii, more than 8,000 kilometers from the Chicxulub crater. Kyte said that fragment, regarding a tenth of an inch in diameter, came from the impact, but other scientists were skeptical that any chunk of the meteor might have survived.
“It actually matches what Frank Kyte was telling us years ago,” DePalma said.
In an email, Kyte said it was impossible to make an assessment without seeing the data. “Personally, I hope that if there is any meteoritic material in these ejected fragments, it would be extremely rare and unlikely to be found in the vast volumes of other debris that were also ejected at this site,” he said. “But maybe they were lucky.”
DePalma commented that there also appear to be bubbles inside some of the spherules. Since the spherules don’t appear to be cracked, they may contain bits of air from 66 million years ago.
In the talk, DePalma also showed off other fossil finds, including a well-preserved leg from a dinosaur identified as a herbivorous Thescelosaurus. “This animal was preserved in such a way that three-dimensional impressions of the skin were left,” she said.
There is no indication that the dinosaur was killed by a predator or by disease. This suggests that the dinosaur might have died on the day of the meteor impact, perhaps drowning in the waters that flooded Tanis.
“This is like analyzing a dinosaur crime scene,” DePalma said. “But as a scientist, I’m not going to say, ‘Yes, we’re 100 percent sure; we have an animal that died in the avalanche caused by the impact,’” he added. “It’s compatible? Yes”.
Neil Landman, curator emeritus of the division of paleontology at the American Museum of Natural History in New York, visited Tanis in 2019. He saw one of the paddlefish fossils with spherules in its gills and is convinced that the site does indeed reflect the day of the cataclysm and its immediate followingmath. “It’s authentic,” he declared.