An undersea crater off West Africa may have formed as a result of the impact of part of an asteroid that killed the dinosaurs.
A 9-kilometer-wide crater has been discovered under the sea floor off the coast of West Africa. The crater was created around the time of the great Chicxulub effect that killed the dinosaurs. The crater may have been caused by debris from the Chicxulub asteroid.
“It definitely looks like a crater,” said geologist Uisdean Nicholson of Heriot-Watt University in Edinburgh, Scotland. Nicholson discovered the suspected crater in seismic reflection data from the oil and gas industry. Nadir Crater, named after a neighboring seamount, is located on the continental shelf several hundred kilometers off the coast of Guinea. It was buried under about 300 meters of sediment in an area of 900 meters water depth.
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Nicholson said the hull has all the hallmarks of an impact crater of this size, including a raised rim and markings of ejected material outside the crater itself. Associate researcher Veronica Bray from the University of Arizona in Tucson models that the crater was caused by the impact of an asteroid about 400 meters in diameter.
Nader Crater appears to have formed about 66 million years ago, around the same time as the 180-kilometre-wide Chicxulub crater in present-day Mexico. That led the team to speculate that the crater was formed from debris from the Chicxulub asteroid, estimated to be 13 kilometers in diameter.
If the debris had broken off just before the impact, the two craters would have been very close to each other. So Nicholson suspects that the asteroid actually disintegrated during a previous pass on Earth due to gravity. This resulted in the two falling within a few days of each other.
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This also happened with Comet Shoemaker-Levy, Nicholson says. It was ripped apart by Jupiter’s gravity in 1992, before it struck the planet in 1994. At least 21 fragments of Jupiter struck within six days.
It’s possible, Nicholson says, that the Chicxulub asteroid also broke into multiple pieces. Other impact craters may not have been discovered, or they may have been obliterated by tectonic processes. Also, no craters form when asteroids end up in waters several kilometers deep, like most of our oceans.
“This is an exciting discovery,” said planetary scientist Gareth Collins of Imperial College London, who has studied the Chicxulub effect. “There are certainly many characteristics that go along with the weft.”
However, Collins is not convinced that the event is linked to the Chicxulub effect. He points out that there is a lot of uncertainty about dating. “I think it’s more likely that the two events are unrelated,” he says.
Nicholson also keeps this option open. His team made a proposal to excavate and extract the Nader crater. These can confirm whether it is an impact structure, and allow a more accurate dating of the event.
Nicholson says that a rare effect alone would not have caused a major extinction wave. It is said that the event mainly affected the surrounding area, causing a tsunami that would have been 500 meters high near the impact site. “It could have been a very significant local event,” Nicholson says.
It could be a rare asteroid that has also caused some global warming by releasing carbon from the blackened shale rocks it hit and destabilizing methane hydrates on the sea floor.
The Chixculub effect was about a thousand times stronger, covering the entire planet in dust within hours. He wiped out all the dinosaurs (except birds), and put a decisive end to the Cretaceous period. Paleontologists have discovered a site in North Dakota that they believe contains fossils of animals killed by the impact.