No, not that asteroid, which wiped out the dinosaurs to extinction, but a previously unknown crater 248 miles off the coast of West Africa that was created around the same time. Further study of the Nader Crater, as it is called, could destabilize what we know about that disastrous moment in natural history.
Uisdean Nicholson, an assistant professor at Heriot-Watt University in Edinburgh, happened to crater by accident — he was reviewing seismic survey data for another project on the tectonic split between South America and Africa and found evidence of the crater below 400 meters of seafloor sediment.
“In interpreting the data, (I came across) this very unusual crater-like feature, unlike anything I’ve seen before,” he said.
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 minerals from the crater floor. But it has all the distinguishing features that scientists would expect: the correct ratio of crater width to depth, height of the ridges, and height of the central lift — a mound in the center caused by rocks and sediments pushed up by impact pressure.
Mark said, “The discovery of a ground impact crater is always important, because it is so rare in the geological record. There are less than 200 confirmed impact structures on Earth and very few potential candidates that have not yet been unambiguously confirmed.” 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 might be due to an asteroid.
The most important aspect of this discovery, Boslough said, was that it was an example of a submarine impact crater, of which there are only a few known examples.
“The opportunity to study a crater of this size underwater will help us understand the process of ocean impacts, which are more common but less well-preserved and understood.”
The crater is eight kilometers (5 miles) wide, and Nicholson believes it was most likely caused by an asteroid over 400 meters (1,300 feet) wide that thrust into Earth’s crust.
“The (rare) impact has had dire consequences both locally and regionally — across the Atlantic at least,” Nicholson explained by email.
“There would have been a large earthquake (magnitude 6.5 – 7), and the ground shook significantly locally. The roar of the atmospheric blast could have been heard all over the world, and it would have caused severe local damage throughout the region.
It would have caused an “exceptionally large” tsunami 3,200 feet (1 kilometer) high around the crater, dissipating to a height of about five meters once it reached South America.
“At 400 meters or so, the atmospheric eruption (which caused the West African crater) was 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 – a margin or error of about a million years – about its exact age.
It’s possible, Nicholson said, that the asteroid impact is related to the Chicxulub effect, or it could just be a coincidence – an asteroid of this size will hit Earth every 700,000 years.
If the asteroid is bound, it could have been the result of an original asteroid disintegration near Earth — with separate fragments scattered during Earth’s previous orbit, or it could have been part of a long-lived asteroid shower that struck Earth over the course of a million years or so.
“Knowing the exact age is really crucial to testing this – again, it can only be achieved by digging.”
Even if it were related, he said, it might be diminished by the Chicxulub effect, but it would have added to the overall set of cascading results.
“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 raises some interesting new questions,” Nicholson said.
“If there are two collisions at the same time, maybe there are other craters there, and what is the cascading effect of multiple collisions?”
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