8 km underwater crater from when dinosaurs disappeared is discovered

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An asteroid from space hit the Earth’s surface 66 million years ago, leaving a huge crater under the sea and wreaking havoc on the planet.

No, it’s not that asteroid, the one that doomed the dinosaurs to extinction, but a previously unknown crater 399 kilometers off the coast of West Africa that was created around the same time. Further study of Nadir Crater, as it is called, could shake what we know about this cataclysmic moment in natural history.

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Uisdean Nicholson, an assistant professor at Heriot-Watt University in Edinburgh, bumped into 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. deep in the sea.

“While interpreting the data, I (come across) this very unusual crater-like feature, unlike anything I had seen before,” he said.

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“It had all the characteristics of an impact crater.”

To be absolutely sure the crater was caused by an asteroid strike, he said it would be necessary to drill into the crater and test minerals from the bottom of the hole.

But it has all the features scientists would expect: the right ratio of crater width to depth, the height of the rims and the height of the central ridge — a mound in the center created by rock and sediment forced by the pressure of the shock.

The journal Science Advances published the study on Thursday (18).

“The discovery of a terrestrial impact crater is always significant because they are very rare in the geological record. There are fewer than 200 confirmed impact structures on Earth and a few likely candidates that have not yet been unambiguously confirmed,” said Mark Boslough, research professor in Earth and Planetary Sciences at the University of New Mexico.

He was not involved in this research, but agreed that it was likely caused by an asteroid.

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

“The opportunity to study an underwater 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.”

cascading consequences

The crater is eight kilometers wide, and Nicholson believes it was likely caused by an asteroid more than 400 meters wide that struck the Earth’s crust.

Although much smaller than the city-sized asteroid that caused the 100-mile-wide Chicxulub crater that slammed into the coast of Mexico and led to the mass extinction of much of life on the planet, it is still a pretty sizable space rock.

“The (Nadir) impact would have severe consequences locally and regionally — at least across the Atlantic Ocean,” Nicholson explained via email.

“There would have been a big earthquake (magnitude 6.5 — 7), so significant in the ground shaking locally. The air blast would have been heard around the world and would have caused severe local damage across the region.

It would have caused an “exceptionally large” tsunami wave a kilometer around the crater, dissipating to about five meters high when it hit South America.

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

“At 400 meters or more, the air blast (which caused the crater in West Africa) would have been much larger.”

Microfossil information from 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 about 1 million years — about its exact age.

Nicholson said it was possible that the asteroid impact was linked to the Chicxulub impact, or it could simply be a coincidence — an asteroid this size would hit Earth every 700,000 years.

If turned on, the object could be the result of a breakup of a parent asteroid near Earth – with the separate fragments scattered during a previous orbit of the planet, or it was possible that it was part of a longer-lived shower of asteroids that hit Earth. Earth over a period of one million years or more.

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

“Understanding the exact nature of the relationship with Chicxulub (if any) is important for understanding what was happening in the inner Solar System at that 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 ripple effect of multiple collisions?”

Source: CNN Brasil

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