Shards of asteroid that killed dinosaurs likely found
Shards of asteroid that killed dinosaurs likely found
The object that slammed off the Yucatán Peninsula of what is today Mexico was about 6 miles wide, scientists estimate, but the identification of the object has remained a subject of debate
By Kenneth Chang
Published: Apr 9, 2022
In a photo provided by NASA, Robert DePalma, a paleontologist, gives a presentation on his findings of fossilized remains at the Goddard Space Flight Center in Greenbelt, Md., on Wednesday, April 6, 2022. Pristine slivers of the impactor that killed the dinosaurs have been discovered, said scientists studying a North Dakota site that is a time capsule of that calamitous day 66 million years ago. (Taylor Mickal/NASA via The New York Times)
GREENBELT, Md. — Pristine slivers of the impactor that killed the dinosaurs have been discovered, said scientists studying a North Dakota site that is a time capsule of that calamitous day 66 million years ago.
The object that slammed off the Yucatán Peninsula of what is today Mexico was about 6 miles wide, scientists estimate, but the identification of the object has remained a subject of debate. Was it an asteroid or a comet? If it was an asteroid, what kind was it — a solid metallic one or a rubble pile of rocks and dust held together by gravity?
“If you’re able to actually identify it, and we’re on the road to doing that, then you can actually say, ‘Amazing, we know what it was,’” Robert DePalma, a paleontologist spearheading the excavation of the site, said Wednesday during a talk at the NASA Goddard Space Flight Center in Greenbelt.
A video of the talk and a subsequent discussion between DePalma and prominent NASA scientists will be released online in a week or two, a Goddard spokesperson said. Many of the same discoveries will be discussed in “Dinosaurs: The Final Day,” a BBC documentary narrated by David Attenborough, which will air in Britain this month. In the United States, the PBS program “Nova” will broadcast a version of the documentary next month.
A New Yorker article in 2019 described the site in southwestern North Dakota, named Tanis, as a wonderland of fossils buried in the aftermath of the impact some 2,000 miles away. Many paleontologists were intrigued but uncertain about the scope of DePalma’s claims; a research paper published that year by DePalma and his collaborators mostly described the geological setting of the site, which once lay along the banks of a river.
When the object hit Earth, carving a crater about 100 miles wide and nearly 20 miles deep, molten rock splashed into the air and cooled into spherules of glass, one of the distinct calling cards of meteor impacts. In the 2019 paper, DePalma and his colleagues described how spherules raining down from the sky clogged the gills of paddlefish and sturgeon, suffocating them.
Usually the outsides of impact spherules have been mineralogically transformed by millions of years of chemical reactions with water. But at Tanis, some of them landed in tree resin, which provided a protective enclosure of amber, keeping them almost as pristine as the day they formed.
In the latest findings, which have not yet been published in a peer-reviewed scientific journal, DePalma and his research colleagues focused on bits of unmelted rock within the glass.
“All these little dirty nuggets in there, every single speck that takes away from this beautiful clear glass is a piece of debris,” said DePalma, a graduate student at the University of Manchester in England and an adjunct professor at Florida Atlantic University.
Finding amber-encased spherules, he said, was the equivalent of sending someone back in time to the day of the impact, “collecting a sample, bottling it up and preserving it for scientists right now.”
Most of the rock bits contain high levels of strontium and calcium — indications that they were part of the limestone crust where the meteor hit.
But the composition of fragments within two of the spherules were “wildly different,” DePalma said.
“They were not enriched with calcium and strontium as we would have expected,” he said.
Instead they contained higher levels of elements like iron, chromium and nickel. That mineralogy points to the presence of an asteroid, and in particular a type known as carbonaceous chondrites.
“To see a piece of the culprit is just a goose-bumpy experience,” DePalma said.
The finding supports a discovery reported in 1998 by Frank Kyte, a geochemist at UCLA. Kyte said he had found a fragment of the meteor in a core sample drilled off Hawaii, more than 5,000 miles from the Chicxulub crater. Kyte said that fragment, about one-tenth of an inch across, came from the impact event, but other scientists were skeptical that any bits of the meteor could have survived.
“It actually falls in line with what Frank Kyte was telling us years ago,” DePalma said.
In an email, Kyte said it was impossible to evaluate the claim without looking at the data. “Personally, I expect that if any meteoritic material is in this ejecta, it would be extremely rare and unlikely to be found in the vast volumes of other ejecta at this site,” he said. “But maybe they got lucky.”
DePalma said there also appear to be some bubbles within some of the spherules. Because the spherules do not look to be cracked, it’s possible that they could hold bits of air from 66 million years ago.
In the talk, DePalma also showed other fossil finds, including a well-preserved leg of a dinosaur, identified as a plant-eating Thescelosaurus. “This animal was preserved in such a way that you had these three-dimensional skin impressions,” he said.
There are no signs that the dinosaur was killed by a predator or by disease. That suggests the dinosaur might have died the day of the meteor impact, perhaps by drowning in the floodwaters that overwhelmed Tanis.
“This is like a dinosaur CSI,” DePalma said. “Now, as a scientist, I’m not going to say, ‘Yes, 100%, we do have an animal that died in the impact surge,’” he said. “Is it compatible? Yes.”
Neil Landman, curator emeritus in 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 capture the day of the cataclysm and its immediate aftermath. “It’s the real deal,” he said.