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Monday, December 05, 2022

Rare crater: Scientists have discovered a 5-mile-wide crater under the ocean that appeared when dinosaurs disappeared

No, it wasn’t the asteroid that wiped out the dinosaurs, but a previously unknown crater 248 miles off the coast of West Africa, which was formed around the same time. Further study of Nadar Crater, as it is called, may confuse what we know about this devastating moment in natural history.

Eusedin Nicholson, assistant professor at Heriot-Watt University in Edinburgh, happened to stumble upon the crater – he was reviewing seismic survey data for another project on the tectonic divide between South America and Africa and 400 meters of seafloor sediment. Evidence of a crater was found below. ,

“In interpreting the data,[I found]this very unusual crater-like feature, unlike anything I’ve seen before,” he said.

To be absolutely sure that the crater was caused by an asteroid impact, he said it was necessary to drill the crater and test minerals from the bottom of the crater. But it has all the typical features scientists expect: the ratio of the width of the crater to the correct depth, the height of the ridge and the height of the central uplift – the mound in between is pushed up by impact pressure due to rock and sediment.

The study was published Thursday in the journal Science Advances.

“The discovery of ground impact craters is always important, because they are very rare in the geologic record. There are fewer than 200 confirmed collision structures on Earth and very few potential candidates that have not been conclusively confirmed,” Mark said. Boslow, research professor of Earth and Planetary Sciences at the University of New Mexico. He was not involved in the study, but agrees that it may have been caused by an asteroid.

The most striking aspect of the discovery, Boslow said, is that it is an example of an underwater impact crater, of which only a few examples are known.

“The opportunity to study underwater craters of this size will help us understand ocean impact processes, which are more common but less well preserved and understood.”

result flow

The crater is eight kilometers (5 mi) wide, and Nicholson believes it was most likely caused by an asteroid more than 400 meters (1,300 ft) wide pushing into the Earth’s crust.

Although much smaller than the city-sized asteroid that caused the 100-mile-wide Chicxulub crater off the coast of Mexico, which caused the mass extinction of most life on the planet, it is still a giant space rock. .

“The impact (rarely) has serious consequences locally and regionally – at least in the Atlantic,” Nicholson explained by email.

“There will be a major earthquake (magnitude 6.5-7), and the ground shakes violently at the local level. The rumble of the aerial explosion could be heard all over the world, and would cause severe local damage throughout the region.

This would have produced a “very large” tsunami of 3,200 feet (1 kilometer) around the crater, which after reaching South America would have spread to a height of about five meters.

For comparison, in Russia in 1908 a 50-meter-wide asteroid atmospheric explosion, known as the Tunguska He event, razed a forest over an area of ​​1,000 square kilometers.

“At 400 meters or so, the atmospheric eruption (which caused the West African crater) was enormous.”

Information from microfossils in nearby exploration wells suggests that the crater was formed around 66 million years ago – at the end of the Cretaceous period. However, there is still uncertainty – a difference or error of about a million years – about its exact age.

It’s possible that the asteroid impact was related to the Chicxulub impact, or just a coincidence — an asteroid of this size would strike Earth every 700,000 years, Nicholson said.

If the asteroid is bound, it may be the result of the disintegration of the original near-Earth asteroid – with isolated fragments scattered during its past Earth orbit, or it may be part of a longer-lived asteroid rain. which hits the earth in one period. Time. million years or more.

“Testing this requires knowing the exact age—again, this can only be obtained by digging.”

Even if it was related, he said, it may have been less of a Chicxulub effect, but it would add to the overall broader result set.

“Understanding the precise nature of the association with Chicxulub (if any) is critical to understanding what was happening in the inner solar system at the time and raises some interesting new questions,” Nicholson said.

“If two collisions happen at the same time, there could be another crater, and what is the wider impact of multiple collisions?”

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