The asteroid that killed the dinosaurs fell in the northern spring

(CNN) – Imagine a calm day in spring 66 million years ago in what is now North Dakota. Triceratops may have been basking in the sun, while freshwater paddle fish, with their mouths open, searched for plankton in the river.

Seconds later, a 10-meter wall of water advances from the east, then crystal balls begin to fall from the sky, some still on fire as they fall into the river.

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These could be the final moments of the age of the dinosaurs, which ended in disaster when a city-sized asteroid crashed into the shallow ocean off Mexico’s Yucatan Peninsula, wiping out three-quarters of all species from Earth.

An artist’s impression of the site of the Tanis River in North Dakota, moments after the asteroid impact that wiped out the dinosaurs to extinction 66 million years ago.

According to a new study conducted on fossil fish found in tanis fossil bedIn North Dakota, which was killed as a result of the devastating impact, the asteroid collided in the spring.

The moment of impact occurred, at least in the northern hemisphere, at a particularly sensitive stage in the life cycle of many plants and animals.

Melanie During, a doctoral student at Uppsala University in Sweden, and lead author of new studio It was published Wednesday in the academic journal Nature.

dinosaurs asteroid spring

Melanie digs for a paddlefish at the Tanis, North Dakota site.

“I think spring puts a large group of late Cretaceous organisms (plant and animal life) at a very sensitive point because they were foraging for food, tending their young and trying to accumulate resources after the harsh winter,” he told a news conference.

By contrast, the researchers said, ecosystems in the southern hemisphere, which were in the fall when the asteroid collided with Earth, appear to have recovered twice as fast as those in the northern hemisphere.

“Shock Frozen”

How did researchers determine the station where the asteroid collided?

Although there are 3000 km from the crater, the bones of paddlefish and sturgeon are preserved in the rocks at the site of Tanis, In Hill Creek Formationprovides a unique record of what may have been the most important event in the history of life on our planet.

The fish, which was up to a meter in length, died in a horrific manner immediately after hitting the asteroid, and was buried alive by the displaced sediment as a huge body of water was displaced upstream by the impact of the asteroid. Think of the water ripples that occur when you drop a stone into a pond, but on a much larger scale.

Unlike a tsunami, which can take hours to reach Earth after a tidal wave, these moving bodies of water, known as Seiche, arose right after the massive asteroid crashed into the sea.

Paddle fish from the Tanis fossil site.

The researchers are confident that the fish died within an hour of the asteroid impact, not as a result of massive wildfires or the ensuing nuclear winter in the days and months that followed. This is because “shocking balls”—small bits of molten rock dripping into space from the crater, where they crystallized into a glass-like substance—were found in the fish’s gills.

“These balls were tossed into space, some of which may have flown around the moon and then rained on the earth again,” he said while.

Of the fossil bed, he said, “These deposits literally look like a frozen shock. It’s the wildest thing I’ve seen so far, and it’s preserved in a primitive state.”

Additionally, the fish was found beneath a layer of rock known as the iridium anomaly, which is rich in the dense element common to asteroids and rare on Earth. This feature was first revealed to geologists by an asteroid impact more than three decades ago.

geological snapshot

Like tree rings, the skeletons of fossilized fish keep notes of animals’ growth, from their development as embryos to their early demise. Analysis of the thin sheets of bone, as well as the distribution, shape and size of osteocytes, which also fluctuate with the seasons, indicates that they died in the spring.

The team of researchers also examined the chemical signatures of different carbon isotopes in an unlucky paddlefish, and the ratio between different isotopic variables revealed how the availability of its favorite food, plankton, affected its skeleton.

Isotopic records indicate that the fish’s annual growth, which will coincide with the peak summer prey availability, has not yet been reached.

asteroid

A section of fossilized paddle fish bones prepared for analysis at Frei University, Brussels.

else bigger studio From the same site, published last year, he also indicated a similar time frame in the spring, while A Much older study than 1991 On the fossil leaves it is suggested that it happened in June.

While he said he believed the asteroid collision most likely occurred in April, but more research is needed to get a definitive answer.

This type of research has been of great value to paleontologists, said Alvio Alessandro Chiarenza, a postdoctoral researcher and paleontologist at the University of De Vigo in Spain, who was not involved in the study.

“The Tanis site may provide some of the most important insights for understanding this mass extinction: Because we paleontologists have to deal with very imprecise temporal resolution, the opportunity to analyze a picture like this of a geological event can advance our understanding of this mass extinction. A pivotal event in the history of this mass extinction event. Our planet.”

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