Scientists discover an 8 km wide underwater crater created when the dinosaurs disappeared

Dinosaur footprints found in Chinese restaurant 1:00

(CNN) —

An asteroid crashed into Earth's surface 66 million years ago, leaving a huge crater under the sea that wreaked havoc on the planet.

No, it's not the asteroid that doomed the dinosaurs to extinction, but a previously unknown crater 400 kilometers (248 miles) off the coast of West Africa that was created around the same time.

Further study of Nadir Crater, as it is called, could revolutionize what we know about that catastrophic moment in natural history.

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Uisdean Nicholson, an assistant professor at Heriot-Watt University in Edinburgh, came across the crater by accident: He was reviewing seismic survey data for another project on the tectonic divide between South America and Africa and found evidence of the crater below 400 meters. of seabed sediment.

"While interpreting the data, I came across this very unusual crater-like feature, unlike anything I had seen before," he said.

"It had all the characteristics of an impact crater."

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To be absolutely sure the crater was caused by an asteroid impact, he said it would be necessary to drill into it and test the minerals on the crater floor.

But it has all the features scientists would expect: the correct ratio between the width and depth of the crater, the height of the rims and the height of the central uplift, a mound in the center created by rocks and sediments pushed up by pressure. of the impact.

The journal Science Advances published the study on Wednesday.

"The discovery of a terrestrial impact crater is always significant, because they are so rare in the geologic record. There are less than 200 confirmed impact structures on Earth and quite a few likely candidates that have yet to be unequivocally confirmed," said Mark. Boslough, a research professor in Earth and Planetary Sciences at the University of New Mexico.

Boslough was not involved in this research, but agreed that the crater was probably caused by an asteroid.

Boslough said the most significant aspect of this discovery is that it was an example of an underwater impact crater, of which there are only a few known examples.

"The opportunity to study a submarine impact crater of this size would help us understand the process of ocean impacts, which are the most common but least well-preserved or understood."

A diagram, incorporating seismic observations and computer simulations, of how Nadir Crater formed.

multiple consequences

The crater is 8 kilometers (5 miles) wide, and Nicholson thinks it was probably caused by an asteroid more than 400 meters (1,300 feet) wide that slammed into Earth's crust.

While it's much smaller than the city-sized asteroid that caused the 100-mile (160-kilometer)-wide Chicxulub crater to hit the coast of Mexico and cause the mass extinction of much of life on the planet, it's still being quite a sizable space rock.

"The (Nadir) impact would have had severe consequences locally and regionally, at least across the Atlantic Ocean," Nicholson explained by email.

"There was a large earthquake (magnitude 6.5 - 7), so significant that it shook the earth locally. The air blast would have been heard around the world and caused severe local damage throughout the region."

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It would have caused an "exceptionally large" tsunami wave of up to 1 kilometer (3,200 feet) around the crater, fading to about five meters high once it reached South America.

By comparison, the midair explosion of a much smaller 50-meter-wide asteroid in 1908 in Russia, known as the Tunguska event, leveled a forest in an area of ​​1,000 square kilometers.

"At about 400 meters, the airburst (which caused the crater off West Africa) would have been much larger."

Information from microfossils in nearby exploration wells shows that the crater formed about 66 million years ago, at the end of the Cretaceous period.

However, there is still uncertainty (margin or error of around 1 million years) about its exact age.

Nicholson said it was possible the asteroid's impact was related to the Chicxulub impact, or it could just be a coincidence: An asteroid this size would hit Earth every 700,000 years.

If linked, the asteroid could be the result of a breakup of a parent asteroid near Earth, with the separate fragments scattered during a previous orbit of Earth, or it was possible that it was part of an asteroid shower that hit Earth. over a period of a million years or so.

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"Finding out the precise age is really critical to testing this, again it's only possible by drilling."

Even if it was linked, it would have been overshadowed by the Chicxulub impact, but it would still have added to the overall set of multiple consequences, he said.

"Understanding the exact nature of the Chicxulub relationship (if any) is important to understanding what was happening in the inner solar system at the time and raised some interesting new questions," Nicholson said.

"If there were two impacts at the same time, could there be other craters out there and what was the cascading effect of multiple collisions?"

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