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An asteroid from space crashed into the Earth’s surface 66 million years ago, leaving a huge crater under the sea and wreaking havoc on the planet.
No, it wasn’t this asteroid, the one that doomed the dinosaurs to extinction, but a previously unknown crater 248 miles off the coast of West Africa that was created roughly at the same time. Further study of the Nadir crater, as it is called, could upend what we know about this cataclysmic moment in natural history.
Uisdean Nicholson, assistant professor at Heriot-Watt University in Edinburgh, stumbled 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 under 400 meters of seafloor sediment.
“In interpreting the data, I (came across) this very unusual crater-like feature, unlike anything I had ever seen before,” he said.
“It had all the characteristics of an impact crater.”
To be absolutely certain the crater was caused by an asteroid impact, he said it would be necessary to drill into the crater and test for minerals from the crater floor. But it has all the characteristics scientists would expect: the right ratio of crater width to depth, the height of the rims, and the height of the central uplift – a mound in the center created by rock and sediment forced by the shock pressure.
The newspaper Science Advances published the study Thursday.
“The discovery of an Earth impact crater is always significant, as they are very rare in the geological record. There are less than 200 confirmed impact structures on Earth and a number of probable candidates that have not been unequivocally confirmed,” said Mark Boslough, research professor of earth and planetary sciences at the University of New Mexico.He was not involved in this research but agreed that it had likely been caused by an asteroid.
Boslough said the most significant aspect of this find is that it was an example of an underwater 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 the least well preserved or understood.”
The crater is 8 kilometers (5 miles) wide and Nicholson believes it was likely caused by an asteroid more than 400 meters (1,300 feet) wide that rushed through the Earth’s crust.
Although much smaller than the city-sized asteroid that caused the 100-mile-wide Chicxulub crater that struck off the coast of Mexico which led to the mass extinction of much life on the planet, it’s still a pretty significant space rock.
“The (Nadir) impact would have had serious consequences locally and regionally – at least in the Atlantic Ocean,” Nicholson explained via email.
“There would have been a large earthquake (magnitude 6.5 – 7), therefore significant tremors on the ground locally. The airburst was reportedly heard around the world and itself caused severe local damage throughout the region.
This would have caused an “unusually large” tsunami wave up to 3,200 feet high (1 kilometer) around the crater, dissipating about five meters high once it reached South America.
By comparison, the 1908 mid-air explosion of a much smaller 50-meter-wide asteroid in Russia, known as the Tunguska Event razed a forest over an area of 1,000 square kilometers.
“At about 400 meters, the air blast (which caused the crater off West Africa) would have been an order of magnitude larger.”
Information from microfossils in nearby exploration pits shows that the crater was formed around 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 impact was related to the Chicxulub impact, or it was just a coincidence – an asteroid of that size would hit Earth every 700,000 years.
If bound, the asteroid could be the result of a breakup from a near-Earth parent asteroid – with the separate fragments scattered during a previous Earth orbit, or it was possible it was part from a shower of longer-lived asteroids. which struck the Earth over a period of about a million years.
“Knowing the precise age is really key to testing this – again, this is only possible by drilling.”
Even if tied, it would have been overshadowed by the impact of Chicxulub, but it would still have added to the overall cascading consequences, he said.
“Understanding the exact nature of the relationship with Chicxulub (if any) is important to 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 there, and what was the cascading effect of multiple collisions?”