The discovery of a large impact crater under the North Atlantic Ocean reveals that more than one asteroid could have killed the dinosaurs.
A newly discovered impact crater beneath the seafloor suggests that more than one asteroid may have hit Earth around the time the dinosaurs went extinct.
Scientists have discovered evidence of an asteroid impact crater under the North Atlantic Ocean. It could force researchers to rethink how dinosaurs came to the end of their reign.
The team believes the crater was caused by an asteroid that collided with Earth about 66 million years ago. It is at the same time that the asteroid Chicxulub hit the Earth off the coast of present-day Yucatan, Mexico, and wiped out the dinosaurs.
“This would have generated a tsunami over 3,000 feet high, as well as an earthquake over magnitude 6.5.” — Veronica Bray
Spanning more than 8 km in diameter, the crater was discovered through seismic measurements, which allow scientists to probe what lies beneath the Earth’s surface.
Veronica Bray, a research scientist at the University of Arizona’s Lunar and Planetary Laboratory, co-authored a study in Science Advances detailing the discovery. She specializes in craters found throughout the solar system.
Named after a nearby seamount, Nadir Crater is buried up to 1,300 feet (400 meters) below the sea floor about 250 miles (400 km) off the coast of Guinea, West Africa. According to the research team, the asteroid that created the newly discovered Nadir Crater could have been formed by the breakup of a parent asteroid or by an asteroid swarm in that time period. If confirmed, the crater will be one of less than 20 confirmed marine impact craters on Earth.
Veronica Bray, pictured here during a visit to Meteor Crater in northern Arizona, is an expert on cratering. Credit: Sarah Sutton/Lunar and Planetary Laboratory
What impact would the asteroid have had?
Bray used computer simulations to determine what type of collision took place and what the effects might have been. Simulations suggest the crater was caused by a 1,300-foot-wide (400-meter-wide) asteroid crashing into 1,600 to 2,600 feet (500 to 800 meters) of water.
“This would have generated a tsunami over 3,000 feet high, as well as an earthquake over magnitude 6.5,” Bray said. “Although much smaller than the global cataclysm of the Chicxulub impact, Nadir will have contributed significantly to the local devastation. And if we have found a Chicxulub ‘brother’, it begs the question: Is there a ‘others?’
The asteroid’s estimated size would put it about the size of asteroid Bennu, the target of OSIRIS-REx, NASA’s asteroid sample return mission led by UArizona. According to Bray’s calculations, the energy released by the impact that caused the Nadir crater would have been about 1,000 times greater than the tsunami caused by the massive underwater eruption of the Hunga Tonga-Hunga Ha’apai volcano in the Polynesian country of Tonga in January 15.
“These are preliminary simulations and need to be refined as we get more data,” Bray said, “but they provide important new insights into the possible ocean depths in this area at the time of impact.”
What is the crater like?
The crater was discovered somewhat by accident by Uisdean Nicholson, a geologist at Heriot-Watt University in Edinburgh. He was examining seafloor seismic reflection data during a research project devoted to seafloor spreading, the geological process that caused the African and American continents to separate, opening up the Atlantic Ocean.
“I have interpreted a lot of seismic data in my time, but I had never seen anything like this. Instead of the flat sedimentary sequences I expected on the plateau, I found a depression 8.5 kilometers below the sea floor, with features very unusual,” said Nicholson. “It has particular features that point to a meteorite impact crater. It has a raised rim and a very prominent central uplift, which is consistent for large impact craters.
“It also has what appears to be ejecta outside the crater, with very chaotic sedimentary deposits extending tens of kilometers outside the crater,” he added. “The features are simply not consistent with other cratering processes such as salt retreat or volcanic collapse.”
The asteroid crashed at the same time as the dinosaur killer
“Nadir Crater is an incredibly exciting discovery of a second impact near the Cretaceous-Paleogene extinction,” said study co-author Sean Gulick, an impact expert at the University of Texas at Austin. “Although it is much smaller than the extinction that caused the Chicxulub impactor, its very existence compels us to investigate the possibility of an impact cluster in the late Cretaceous.”
According to the seismic data, the sediments impacted by the asteroid probably correspond to the Cretaceous-Paleogene boundary: a sedimentary layer that delimits the end of the Cretaceous period and the last known appearance of dinosaurs. However, there is some uncertainty about the precise timing of the impact, limited by the resolution of the data.
“Despite 4 billion years of impactors hitting Earth, only 200 have been discovered,” Gulick said. “So it’s exciting news every time a new potential impact is discovered, especially in the hard-to-explore marine environment.”
Nicholson has already applied for funding to drill into the seabed to confirm it is an asteroid impact crater and test its precise age.
Reference: “The Nadir Crater offshore West Africa: A candidate Cretaceous-Paleogene impact structure” by Uisdean Nicholson, Veronica J. Bray, Sean PS Gulick and Benedict Aduomahor, 17 Aug 2022, Science Advances.DOI: 10.1126/sciadv. abn3096