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WASHINGTON (WASHINGTON POST) – Sixty – six million years ago, a huge asteroid crashed into a shallow sea near Mexico. The impact dug a crater 140 km wide and projected mountains of land in space. Earth-bound debris has fallen on the planet in the form of rock droplets and molten glass.
The ancient fish caught drops of glass in their gills as they swam their mouths in the weird rain. Big waves threw the animals on dry land, then more waves burrowed them in the silt. Scientists working in North Dakota have recently discovered fossils of these fish: they died in the first minutes or hours after the collapse of the asteroid, according to an article published on Friday. March in the Proceedings of the National Academy of Sciences. aroused immense emotion among paleontologists.
"You are coming back to the day of dinosaur death," said Timothy Bralower, a paleoceanographer at Pennsylvania State University, who studies the impact crater and did not participate in this work. "It's what it is – it's the day the dinosaurs are dead."
About three out of four species perished in what is called Cretaceous-Paleogene extinction, also known as the K-Pg event or K-T extinction. The killer asteroid has the most famous claimed dinosaurs. But T. rex and Triceratops were joined by hordes of other living beings. Freshwater and marine creatures have been the victims, as have plants and micro-organisms, including 93% plankton. (A single branch of dinosaurs, the birds, continues to live.)
Four decades of research support the theory of asteroid extinction, widely regarded as the most plausible explanation for the disappearance of dinosaurs. In the late 1970s, Luis and Walter Alvarez, a father-son science duo at the University of California at Berkeley, examined an unusual geological layer between the Cretaceous and Paleogene periods. The border was full of the element iridium, which is rare in the Earth's crust, but not in asteroids.
Walter Alvarez is one of the authors of the new study.
The Hell Creek fossils represent "the first assemblage of large bodies dead by death that anyone found" which lies on the edge of K-Pg, said study author Robert DePalma, in a statement.
DePalma, a Ph.D. student at the University of Kansas, began digging the Hell Creek, North Dakota site in 2013. Since then, DePalma and other paleontologists have discovered piles of water. sturgeons and fossilized polyodons, still covered with glass spheres.
They found squid-like animals called ammonites, shark teeth and the remains of predatory aquatic lizards called mosasaurs. They found dead mammals, insects, trees and a Triceratops. They found one-foot fossil feathers, traces of dinosaurs and prehistoric mammal burrows. They found a parcel of fossilized tree called amber that had also captured the glass spheres.
The site contains "all Chicxulub impact mark signals," said Bralower, including glass beads and a lot of iridium. In the geological layer just above the fossil bed, ferns dominate, signs of an ecosystem being restored. "It's bewitching," he says.
In the early 1990s, researchers located the scar left by the asteroid, a crater on the Yucatan Peninsula. The impact was named after the neighboring Mexican city of Chicxulub.
The "destruction mechanisms" suggested for the impact of Chicxulub abound: it may have poisoned the planet with heavy metals, rendered acidic acid, wrapped the Earth in darkness or set off a global fire storm. His punch may have triggered volcanoes that spit like cans of soda.
Hell Creek is more than 3,000 km from Chicxulub Crater. But a rain of glass beads, called tektites, rained down within 15 minutes after the impact, said study author Jan Smit, paleontologist at Vrije University in Amsterdam, who also discovered iridium at the K-Pg limit.
The fish, pressed into the mud like flowers in a diary, are remarkably well preserved. "It's the equivalent of finding people occupying vital positions buried by ashes after Pompeii," Bralower said.
At the time of the dinosaurs, the Hell Creek site was a river valley. The river fed an inland sea connecting the Arctic Ocean to a prehistoric Gulf of Mexico. According to the study authors, after the asteroid strike, seismic waves of magnitude 10-11 earthquake have crossed this sea.
This did not cause tsunami, but rather what are called cuttlefish waves, the round-trip sloshes sometimes seen in miniature in a bathtub. It can be symptoms of very distant tremors, such as the cuttlefish waves that swept through the Norwegian fjords in 2011 after the giant Tohoku earthquake near Japan.
Inland sea squid waves reached 9 m, drowning the river valley with water, gravel and sand. The rain of rocks and glass followed. The tektites have dug "small funnels into the sediments deposited by the cuttlefish," Smit said, "then you know for sure that they are coming down when the waves continue to rise." It is the preservation, in other words, of a new hell.
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