Chicxulub, the asteroid that wiped out most of the dinosaurs, could have had a little brother.
Off the coast of West Africa, hundreds of meters below the seabed, scientists have identified what appear to be the remains of a 8.5 kilometer wide impact crater, whom they have called Nadir. The team estimates that the crater formed around the same time as another asteroid: Chicxulubthe dinosaur killer, crashed into modern Mexico (Serial number: 01/25/17). If confirmed, it could mean that non-bird dinosaurs met their demise from a double hit by asteroids, researchers report in August 17. Progress of science.
“The idea that [Chicxulub] had help, for lack of a better phrase, would really have added insult to injury,” says study co-author Veronica Bray, a planetary scientist at the University of Arizona in Tucson.
Narrowly 200 impact craters have been discovered on Earth (Serial number: 12/18/18), the vast majority of which are found on land. That’s because impact craters in the sea are gradually buried under sediment, Bray says, making the Nadir structure a valuable scientific find, regardless of its date of birth.
Geologist Uisdean Nicholson of Heriot-Watt University in Edinburgh found the structure while analyzing data collected by seismic waves transmitted underground to detect physical structures offshore Guinea. Lurking beneath the seabed, and under almost 1 kilometer of water, he made out a bowl-shaped structure with a broken terraced floor and a pronounced central peak, features expected of a large impact.
Based on the dimensions of the structure, Bray, Nicholson and their colleagues calculate that if an asteroid were responsible for the terrain, it would probably be more than 400 meters wide. In addition, the researchers estimate that the impact would have shaken the ground like a magnitude 7 earthquake and triggered tsunamis hundreds of meters high.
Despite the consequences, the Nadir impact would have been far less devastating than that of the roughly 10-kilometre-wide Chicxulub asteroid, says Michael Rampino, a geologist at New York University who was not involved in the study. “It certainly wouldn’t have had global effects,” he says.
Using geological layers adjacent to Nadir, some with ages obtained from previous studies, the team estimated that the structure formed around the end of the Cretaceous period, 66 million years ago. Asteroid Nadir may even have formed a pair with asteroid Chicxulub, the two of which were ripped apart by gravitational forces during an earlier flyby of Earth, the researchers speculate.
But the study’s conclusions have some experts cautious. “It looks like an impact crater, but it could also be something else,” says geologist Philippe Claeys of the Vrije Universiteit Brussel in Belgium, who was not involved in the research. Confirming that the structure is an impact crater will require drilling for solid evidence, such as impacted quartz, he says. Alternative explanations for the structure’s identity include a collapsed volcanic caldera or a squeezed-out salt body called a salt diapir.
The age of the Nadir structure is another uncertainty. Seismic data shows that it appears to have formed sometime near the end of the Cretaceous period or perhaps a little later, says Claeys. “But that’s the best they can say.” Drilling into the crater for minerals containing radioactive elements could provide a more precise date of formation, says Rampino.
It is not the first time that scientists have investigated whether Chicxulub had an accomplice. Some studies have suggested that the Boltysh crater in the Ukraine may have formed at the same time as Chicxulubalthough researchers have since determined that Boltysh formed 650,000 years later.
Bray and his colleagues are currently negotiating funds to collect samples from the crater, with aspirations to drill in 2024. Hopefully, that will resolve some of the debate around Nadir’s origins, Bray says, though it will likely raise new questions as well. “If we prove that this is the sister of the dinosaur killer, how many other siblings are there?”