Earth still bears the scar of the giant asteroid impact that wiped out the dinosaurs, along with three-quarters of all life – but new research suggests the killer rock wasn’t the only one. Scientists have discovered a new crater on the North Atlantic seafloor that appears to correspond to around the same time, suggesting the extinction event may have been triggered by multiple impacts.

Nadir Crater, as it is named, is about 8.5 km (5.3 mi) wide and is located about 400 km (250 mi) off the coast of Guinea, West Africa. Geologist Wisdean Nicholson was studying seismic reflection data on the Guinea Plateau, a large area of ​​flat seafloor, when he noticed a strange structure buried about 300 to 400 m (985 to 1,310 ft) underground.

“I’ve interpreted a lot of seismic data in my time, but I’ve never seen anything like this,” Nicholson said. “It has specific features that point to a meteorite impact crater. It has a raised rim and a very prominent central ridge that is consistent with large impact craters. In addition, there is what appears to be an ejecta outside the crater, with many chaotic sedimentary deposits extending for tens of kilometers outside the crater. The features are simply not consistent with other cratering processes such as salt withdrawal or volcanic collapse.”

Studies of the sediment stirred up during the impact suggest that Nadir Crater formed about 66 million years ago, at the end of the Cretaceous period. It famously marked the extinction that took out the dinosaurs, believed to have been caused by a massive asteroid impact, still visible as the Chicxulub Crater in Mexico.

The researchers used computer simulations to study what type of impactor under what conditions would have been needed to produce the crater seen, as well as how bad the fall might have been. They found that the asteroid responsible was probably about 400 m (1,300 ft) wide and appeared to have hit a body of water between 490 and 790 m (1,600 and 2,600 ft) deep.

“This would generate a tsunami over 3,000 feet (915 m) high, as well as an earthquake over magnitude 6.5,” said Veronica Bray, co-author of the study. “Although much smaller than the global cataclysm of the Chicxulub impact, the nadir would have contributed significantly to the local devastation. And if we find one ‘brother’ of Chicxulub, that opens the question: Are there others?’

The discovery could change our understanding of this key extinction event. Rather than just one large rock, this could indicate that Earth encountered a swarm of asteroids at the time, or that the parent body broke into several pieces before impact.

Of course, it is difficult to pinpoint the exact timing of the two impacts – they could have happened thousands, even millions, of years apart. The team plans to investigate further by drilling into the sea floor at the site to confirm that it is an impact crater and determine its age more precisely.

The study was published in the journal Scientific progress.

source: University of Arizona

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