Second Crater Bolsters Double Impact Theory

Sharp, three-dimensional seismic data of a seafloor crater off Guinea seems to confirm that a second asteroid hit Earth at approximately the same time as the behemoth that hit North America 66 million years ago, ending the reign of the dinosaurs.

A team of researchers recently imaged the 5.28-mile-wide (8.5-kilometer-wide) depression off the African coast, giving the team a much better characterization of the crater’s features. Based on its analysis, the team confirmed the crater’s age and ruminated on the immediate aftermath of the impact.

The dinosaurs—besides the ancestors of modern birds, of course—went extinct 66 million years ago, after a massive asteroid slammed into what is now Mexico’s Yucatán Peninsula at the “deadliest possible angle,” according to a 2020 paper. Research published in 2021 indicated the asteroid probably hit in springtime, but the result would’ve been catastrophic in any weather: 100 million megatons of force threw Earth’s systems out of whack.

Part of the difficulty that dinosaurs and most other walks of ancient life faced was that the asteroid kicked up tsunami waves best measured in miles, as well as dust, soot, sulfur, and more dust that caused the extinction of about 75% of life. In other words, it wasn’t just the cataclysmic impact of a giant rock from space—it was also the aftermath caused by that impact.

But the Chicxulub asteroid evidently didn’t work alone. In 2022, a team including several members of the recent team revealed the bowl-shaped feature and dubbed it the Nadir Crater. The crater is buried under roughly 1,300 feet (400 meters) of sediment on the Guinea Plateau, a swath of continental crust that juts out about 250 miles (400 km) from the coasts of Guinea and Guinea Bissau.

In the new paper, the research team published images of the asteroid impact crater, confirmed its age at 66 million years old, and projected what happened in the immediate aftermath of the impact. The team’s research was published today in Communications Earth & Environment.

In its 2022 paper, the team suggested three potential origins of the crater. One possibility, the researchers said, is that a large asteroid broke off from the same parent body as the Chicxulub asteroid in the Yucatán as it approached Earth. Another option is that some collision in the asteroid belt sent a barrage of asteroids towards Earth in the same, roughly million-year timeframe. A final option is that the timing of the two impacts was pure coincidence: that two giant space rocks hit Earth at roughly the same time, in what was just extra rotten luck for the dinosaurs.

“The asteroid responsible for Chicxulub is far bigger than that which we propose for Nadir,” Uisdean Nicholson, a geoscientist at Heriot-Watt University in Scotland and lead author of both papers, told Gizmodo in 2022. “We would expect around 10,000 times more energy to be released from Chicxulub. So the Nadir impact would have been dwarfed by Chicxulub.”

Just last month, a different team of researchers published work in Science positing that the parent body of the Chicxulub and Nadir asteroids came from well beyond Jupiter, lending credence to the asteroid-belt origin hypothesis.

The team estimated that the Nadir asteroid hit the Earth traveling at about 12.43 miles per second (20 kilometers per second), or nearly 45,000 miles per hour (72,000 km/hr). In a Heriot-Watt University release, Nicholson said that earthquakes caused by the impact “liquified the sediments below the seabed across the entire plateau” and caused large underwater landslides. Based on the sharp images of the crater, the team also projects that the impact caused a half-mile-high (800 meters) tsunami, if not taller.

66 million years ago was already known to be a pretty crappy time to be a living thing on Earth. But confirmation of the Nadir Crater’s age doubles down on that idea. The team has applied to drill into the seabed to recover sediment cores from the crater itself, which will further clarify the force with which the ancient asteroid hit the seafloor and how the immediate aftermath of the event may have unfolded.