A second asteroid may have crashed into Earth as the dinosaurs died

A plateau of shallow ocean was left off Guinea's west coast as a result of the Jurassic Ocean's creation by the separation of Africa and South America. According to Uisdean Nicholson, a marine geologist at Heriot-Watt University in Scotland who researches the area to learn about the formation of the Atlantic, "all the layers are quite flat, almost like a layer cake."

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Thus, in 2017, while Nicholson was reviewing seismic readings of the area made by oil and gas development vessels, a surprising feature—a 5-mile-wide dimple hidden deep in the cake—jumped out.

The site is thought to be the crater from a meteor that was as wide as the Eiffel Tower was tall, according to a closer examination of the location led by Nicholson and published today in the journal Science Advances. It would have struck Earth within a million years of the Chicxulub meteor that wiped off the dinosaurs, if it is determined to be a crater.

Nicholson looked for more explanations for the indentation, including geological activity, a volcano, or methane bubbles that were escaping. But none of them fully described the size, position, and shape of the crater. So he sought assistance from specialists in cosmic impact. According to coauthor and meteor strike expert Sean Gulick of the University of Texas Institute for Geophysics, "almost every week, someone emails me circles they found in seismic data or on Google Earth." However, the indentation, which the team refers to as the Nadir Crater, passed all of their testing. Shapes, proportions, and even modeling are appropriate, claims Gulick.

Veronica Bray, a member of the team and a planetary scientist at the Lunar and Planetary Laboratory in Tucson, ran simulations of many meteor hits in various ocean depths to further support the theory. An approximately accurate replica of the real crater was made when a rock more than 1,000 feet broad impacted the ocean that was half a mile deep. The computer predicted that the rock would descend about a mile down the ocean floor in the first few seconds after impact, vaporizing rocks and water and unleashing a tsunami in all directions.

According to Nicholson, the collision would cause such strong vibrations that "the rocks or dirt below the seafloor become a fluid." He claims that as the surrounding rock around the crater shattered, "you get this tremendous vertical column, like you threw something into a pool." A crater with an elevated pile of solid rock in the middle, similar to what is buried beneath the seafloor of Guinea, is created when that occurs with the water, but it also occurs with the rocks below.

Gulick claims that "the energy engaged in this are immense." "This eruption in Tonga had 1000 times the energy of this one. Magnitude 7.5 or 8 earthquakes would result from it.

While agreeing that the feature's shape is intriguing and merits more study, Ludovic Ferrière, an impact crater specialist from the Natural History Museum Vienna who was not involved in the work, is dubious of the decision to publish based solely on seismic photos. He remarks, "It's a pretty excellent proposal. But it's still too early. In the end, they might be correct, but they might also be totally off.

This little asteroid has a tiny moon all to itself.

Ferrière claims to have discovered other craters that are equally striking. He claims to have discussed the crater with Gulick at a bar days before the publication. But he doesn't believe they would pass scientific examination to be published in the absence of tangible evidence. "You need DNA or blood to find the murderer in a case," he asserts. A crater left by an impact is the same way: The only tangible signs of a meteor are the presence of "shocked" minerals, which only appear in the wake of a cosmic collision, or genuine meteorite spray.

The only way to be certain is to drill from a ship hundreds of feet into the actual seafloor. But this raises a chicken-and-egg issue. The academic organization best suited to take a sample—the International Ocean Discovery Program—would only do so once a peer-reviewed article indicates that it is a good candidate—"at a cost of several million dollars," Nicholson adds over email.

The area will be visited by a ship from the International Ocean Discovery Program in 2023 that can take core samples under hundreds of feet of rock and thousands of feet of water. The team plans to investigate materials from the crater in the coming years and has submitted an application for time with the drill.

The predicted crater's age will be made clearer by the drilling as well. The site is located close to the K-PG boundary, which is where dinosaurs, pterosaurs, and enormous marine reptiles went extinct in a cataclysmic extinction 65 million years ago, according to cores excavated a little more than 100 miles from the projected crater. The Chicxulub meteor, which was miles wide, crashed into what is now the Yucatan Peninsula, causing that die-off.

[Related: When an asteroid wiped off the dinosaurs, it was likely springtime]

However, the sound waves the team is using in Guinea only provide a little hazy image, making it difficult to precisely determine the date. To the best of our knowledge, we are at the boundary, although Nicholson cautions that it could be older or younger by a million years.

Gulick believes that it is unlikely that the Chixculub meteor fragment that broke off during a previous fly-by past Earth produced the crater if it is located right at the border. It might also have been a component of an asteroid swarm that came close to Earth over a period of thousands of years. Without proof that the Nadir Crater is a crater, Ferrière adds, "it's like creating a gigantic castle of stone on something that is not stable." He refers to these theories as "speculation upon speculation."

Even if it is a crater, it may not be related to the Chicxulub impact because a comparably sized meteor strikes Earth every 700,000 years. Gulick, however, asserts that it would be unexpected to find a documented crater within a million years of Chicxulub since they are so uncommon—there are only a little more than 200 confirmed or suspected craters on Earth.