Sixty-six million years ago, a giant meteor slammed into Earth off the coast of modern-day Mexico.
Firestorms incinerated the landscape for miles around. Even creatures thousands of miles away were doomed on that fateful day, if not by fire and brimstone, then by mega-earthquakes and waves of unimaginable size.
Scientists have unearthed a remarkable trove of fossils that appear to date from the very day of the impact. The burial site consists of more than 4 feet of sediments and organic remains that were dumped in North Dakota almost instantly and transformed into rock over the eons. It evidently captures, in unparalleled detail, the repercussions of the giant doomsday rock that cleared the way for the evolution of mammals, including the primates known as humans.
In an article made available to reporters Friday in Proceedings of the National Academy of Sciences, a leading science journal, an international team of 12 scientists described a dig near Bowman, North Dakota, that encapsulated the swift demise of an ancient lake and its inhabitants.
When the meteor smashed into waters near what is Mexico’s Yucatán Peninsula, it left a giant crater known as Chicxulub and prompted upheavals thousands of miles away, including what is North Dakota. Within hours and perhaps minutes of the titanic collision, sea creatures were swept inland by tsunamis and earthquakes, tossed together and deposited with a diverse array of landlocked life, including trees, flowers and vanished types of freshwater fish.
The jumble was swiftly entombed, and exquisitely preserved. Permeating the deposit were tiny spheres of clay and glass, known as tektites, which formed as molten rock, ejected by the impact, showered from the sky.
In the paper, the researchers argue that the fossil bed captures the Chicxulub impact’s immediate ramifications for life on Earth. It appears to be the best-ever snapshot of that day, one that advances the scientific understanding of “the full nature and extent of biotic disruptions that took place,” the authors write.
The lead researcher, Robert DePalma, is a curator of paleontology at the Palm Beach Museum of Natural History, in Florida, as well as a graduate student at the University of Kansas. Thirty-seven years old, he was granted access to the rich fossil bed by a rancher in 2012, then mined it secretly for years. His efforts are detailed in an article in The New Yorker that was posted online Friday.
Gradually, DePalma shared his findings with top scientists, some of whom have joined him as co-authors. They include Walter Alvarez, a geologist at the University of California, Berkeley, who pioneered the idea decades ago that the dinosaur extinction was the result of such a cosmic impact.
The rocks contained a tangle of fossilized trees, branches, fishes and other animals. “You would be blind to miss the carcasses sticking out” of the weathering rock, DePalma said. “It is impossible to miss when you see the outcrop.”
The paper describes how tektites, raining into the water, clogged the gills of fish, which were then killed by surges of water.
The water could have traveled up from the Gulf of Mexico through an inland sea that cut through North America at the time. But the authors argue for another, more likely explanation: that cataclysmic waves from the impact — which produced the equivalent of a magnitude 10 or 11 earthquake — sloshed water out of distant lakes and seas and up their connected river channels.
“It basically agitates water like a washing machine,” said Phillip Manning, a paleontologist at the University of Manchester in England and one of the authors of the paper. “When that shock wave dissipates, it almost instantly drops out what was in this water body.”
Those contents, he said, formed the North Dakota deposit that he, DePalma and their colleagues described in their paper.
DePalma initially was disappointed with what he found, he said. He had hoped that the site would reveal rhythmic seasonal changes over a period of years.
Instead, the material had been dumped in one big surge. “My idea of multi-season pond deposits was out the window,” he said.
In an interview, Steve Brusatte, a vertebrate paleontologist and evolutionary biologist at the University of Edinburgh, called The New Yorker portrayal of the fossil find “a remarkable story” that he wanted to believe. “But it’s disappointing that the dinosaurs are not mentioned in the peer-reviewed paper,” he said. “And because they’re not, there simply isn’t any evidence for me to assess.”
For now, Brusatte said, “I am left with more questions than answers when it comes to the dinosaur aspect of this story.”