An asteroid from space crashed into Earth’s surface 66 million years ago, leaving a massive crater under the sea and wreaking havoc on the planet.
No, it’s not this asteroid that doomed the dinosaurs to extinction, but an unknown crater 399 kilometers (248 miles) off the coast of West Africa that was created at the same time. Further study of Nadir Crater, as it is called, could shake up what we know about this cataclysmic moment in natural history.
Uisdean Nicholson, an assistant professor at Heriot-Watt University in Edinburgh, happened upon the crater: 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 seabed sediment.
“While interpreting the data, I came across this very unusual crater-like feature, unlike anything I’d seen before,” he said.
“It had all the characteristics of an impact crater.”
To be absolutely certain that the crater was caused by an asteroid impact, he said it would be necessary to drill into the crater and test for minerals in the crater floor. But it has all the features scientists would expect: the correct ratio of crater width to depth, the height of the rims, and the height of the central elevation: a mound in the center created by rocks and sediments forced by the shock pressure. .
The journal Science Advances published the study on Thursday.
“The discovery of an Earth impact crater is always significant, because they are very rare in the geologic record. There are fewer than 200 confirmed impact structures on Earth, and quite a few likely candidates that have yet to be formally confirmed unequivocal,” 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 was probably caused by an asteroid.
Boslough said the most significant aspect of this discovery is that it was an example of a submarine 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 oceanic impacts, which are the most common but least well preserved or understood.”
CASCADE CONSEQUENCES
The crater is 8 kilometers (5 miles) wide and Nicholson believes it was probably caused by an asteroid more than 400 meters (1,300 feet) wide that crashed into the Earth’s crust.
Although it is much smaller than the city-sized asteroid that caused the 100-mile-wide Chicxulub crater that hit the coast of Mexico and caused the mass extinction of much of life on the planet, is still a pretty important space rock.
“The (Nadir) impact would have had serious consequences locally and regionally, at least across the Atlantic Ocean,” Nicholson explained by email.
“There would have been a large earthquake (magnitude 6.5 – 7), so the ground shook a lot locally. The air blast would have been heard around the world and caused severe local damage throughout the region
It would have sent an “exceptionally large” tsunami wave up to 3,200 feet (1 kilometer) high around the crater, dissipating 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, flattened a forest over an area of 1,000 square kilometers.
“At 400 meters or so, the blast of air (that caused the crater in West Africa) would have been orders of magnitude 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 one million years) about its exact age.
Nicholson said it was possible the asteroid impact was related to the Chicxulub impact, or it could simply be a coincidence: An asteroid of that 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 could have been part of a shower longest-lived asteroids that hit Earth over a period of about a million years.
“Finding out the precise age is really critical to testing, again, it’s only possible by drilling.”
Even if it had been linked, it would have been dwarfed by Chicxulub’s impact, but would still have added to the overall cascading set of consequences, he said.
“Understanding the exact nature of the relationship with Chicxulub (if any) is important to understanding what was going on 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?”