Chicxulub, the asteroid that killed off most dinosaurs, might have had a younger brother or sister.
Researchers have discovered what looks to be the remains of an 8.5-kilometer-wide impact crater off the coast of West Africa, hundreds of metres beneath the seafloor. The crater created about the same period as another asteroid, Chicxulub, the dinosaur killer, hit into modern-day Mexico. If verified, it might suggest that nonbird dinosaurs were killed by a one-two punch of asteroids, according to a study published in the journal Science Advances on August 17.
“The idea that [Chicxulub] had help — for want of a better phrase — would have really added insult to serious injury,” Veronica Bray, a planetary scientist at the University of Arizona in Tucson, is one of the study’s coauthors.
On Earth, about 200 impact craters have been identified, with the great majority of them being on land. According to Bray, this is because impact craters at sea gradually become buried under silt, making the Nadir structure an important scientific find regardless of its birthday.
The structure was discovered by geologist Uisdean Nicholson of Heriot-Watt University in Edinburgh while analysing data obtained by seismic waves sent underground to find physical features offshore of Guinea. He discovered a bowl-shaped structure with a broken-up, terraced floor and a conspicuous centre peak lurking beneath the bottom – traits anticipated of a massive impact.
Based on the structure’s dimensions, Bray, Nicholson and their colleagues calculate that, if an asteroid was responsible for the terrain, it would probably have been over 400 meters wide. What’s more, the researchers estimate that the impact would have rocked the ground like a magnitude 7 earthquake and stirred tsunamis hundreds of meters high.
Despite that fallout, the Nadir impact would have been far less devastating than the one from the roughly 10-kilometer-wide Chicxulub asteroid, says Michael Rampino, a geologist from New York University who was not involved in the study. “It certainly wouldn’t have had global effects,” he says.
Using geologic strata close to Nadir, some of which had previously received dates, the scientists concluded that the structure developed towards the end of the Cretaceous period – 66 million years ago. According to the researchers, the Nadir asteroid may have formed a pair with the Chicxulub asteroid before being blasted apart by gravitational forces during a previous Earth encounter.
However, other experts are sceptical about the study’s findings. “It appears to be an impact crater, but it may also be something else,” adds geologist Philippe Claeys of Belgium’s Vrije Universiteit Brussel, who didn’t involve in the study. Drilling for solid evidence, such as shocked quartz, will be required to confirm that the feature is an impact crater, he says. A collapsed volcanic caldera or a compressed mass of salt known as a salt diapir are two possible explanations for the structure’s identification.
Another unknown is the age of the Nadir construction. According on the seismic data, it looks to have originated around the end of the Cretaceous era, or maybe a little later, according to Claeys. “But that’s about all they can say.” Rampino believes that drilling in the crater for minerals containing radioactive materials might yield a more exact date of origin.
It’s not the first-time scientists have looked into whether Chicxulub had a helper. Although some studies have claimed that the Boltysh crater in Ukraine originated around the same time as Chicxulub, geologists have now concluded that Boltysh formed 650,000 years later.
Bray and her colleagues are presently negotiating funds to gather crater samples, with plans to drill in 2024. According to Bray, this will perhaps clarify part of the discussion over Nadir’s origins, though new issues will undoubtedly develop. “How many additional siblings are there if we show that she is the dinosaur killer’s sister?”
image credits: Getty images
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