A crater in West Africa dating back to the last days of the dinosaurs has researchers wondering if the giant ancient reptiles collided with several asteroids at once.

This West African crater, hidden under about 900 meters of water and 400 m of sediment, has yet to be directly studied; it was only detected in reconstructions of the ocean floor made using seismic waves.

To prove beyond a doubt that the crater is indeed caused by an asteroid, scientists will need to drill into the structure and find minerals that have undergone shocks of extreme heat and pressure.

A crater in West Africa could be the “brother” of the one that destroyed the dinosaurs

But the shape of the crater points to an extraterrestrial origin, said David Kring, principal investigator at the Lunar and Planetary Institute in the US, who was not involved in the current study but was one of the discoverers of the Chicxulub crater, left by the asteroid that killed the non-avian dinosaurs about 66 million years ago.

“I have to congratulate the team for finding what appears to be a potential impact crater,” Kring told Live Science.

“It’s very important because we have so few impact craters preserved on Earth. Each one we can find provides a new window, new insights into the geological processes that shape them and their effects on Earth’s biological evolution,” said the researcher.

The newly discovered crater formed very close in time to Chicxulub, suggesting the possibility of a connection between the two.

An accidental discovery

When Uisdean Nicholson, a geologist at Heriot Watt University in the UK, and his team began scrutinizing seismic data off the West Coast of Africa, they weren’t looking for signs of space rocks. The goal, Nicholson said, was to study the tectonics that pushed South America away from Africa 100 million years ago.

Seismic data is obtained by sending vibrations from a vessel to the seabed and recording the waves that return. The result shows the basement structure. To the surprise of the researchers, on the bottom of the sea, about 400 kilometers from the coast of Guinea and Guinea-Bissau, they found strange traces in the rock layers.

“This crater in West Africa is very striking and unlike anything we’ve seen before,” Nicholson said.

How big is this crater in West Africa?

What the researchers saw was a roughly circular or elliptical hole about 8.5 km in diameter and up to 40 m deep. The rim of the crater revealed signs of faulting and deformation of the rock, and perhaps even material ejected from the main crater that landed around it after the impact.

One of the telltale features was a structure beneath the crater floor, where layers of rock were raised above the surroundings. This “central uplift” occurs after impacts where the shock pressure is high enough to force pieces of rock to act like a fluid, Nicholson said; the rock basically breaks, falls back, and “freezes” in that configuration forever.

The researchers named the structure Nadir Crater, after a nearby seamount, and reported their findings today in the journal Science Advances.

How big was the asteroid that created Nadir Crater?

The crater would have been caused by an asteroid that was 400 m wide. The asteroid hit the ocean floor with 5,000 megatons of TNT, the researchers calculated, and would have produced a fireball 10 km wide.

This would have instantly vaporized massive amounts of water and rock. The impact would have created a magnitude 7 earthquake that could have triggered a series of undersea landslides, all of which would have created some serious waves.

The spray from the impact site would have been at least 2 km high, Nicholson said, and the waves that reached the West African coast could have been 100 km high. The coast of South America, 1,000 km away at the time, would have been hit by 5m high tsunamis.

Life after impact

Despite this short-term devastation, Kring said, marine life would likely have recovered quickly. In a similar marine crater now on land in Nevada, researchers have found that sediments just above the crater show colonization by new life shortly after the impact, he said.

Based on the rock layers in and around the crater, Nicholson and his team found that it is about 66 million years old, roughly the same age as the impact that created the Chicxulub crater off present-day Yucatán Peninsula, ending the age of dinosaurs.

Chicxulub was created by an asteroid about 10 kilometers in diameter, 25 times larger than the one that probably hit West Africa. The similarity in the chronology makes scientists wonder if there is any connection between the two craters.

Were the dinosaurs killed by multiple asteroids?

It is difficult to answer such questions. The seismic data allows Nicholson and his team to estimate the age of the new crater to within 800,000 years, so it’s possible that the impacts occurred quite far back in time and had nothing to do with the other one.

Because craters on Earth are so often eroded or destroyed by tectonics, it’s easy to forget that impacts are relatively common, geologically speaking, Kring said.

However, there are several scenarios where Chicxulub Crater and Nadir Crater could be connected. The asteroid that killed the dinosaurs may have broken up near Earth and could have hit the planet in several bursts, hours or days apart, Nicholson said.

Or the two space rocks could have come from the same parent asteroid that broke up in the asteroid belt and hit Earth in a cluster of impacts over 1-2 million years.

This crater in West Africa will have to be drilled, but that won’t happen anytime soon

Getting any further details about Nadir Crater would require drilling into the crater floor and extracting rock samples, which could show impact shock minerals that could be analyzed to get a more precise date.

Small fragments of asteroids may still be embedded in the crater. Nicholson said he and his team have submitted a drilling proposal to the International Ocean Discovery Program, but even if the effort is approved and funded, it won’t happen until 2024 or 2025.

Subsea drilling is complicated and expensive. It took a decade for scientists to conduct marine drilling at the Chicxulub impact site after it was identified in 1991, and only two drilling expeditions took place in 30 years. Still, Kring said, Nadir Crater is a tempting place to explore.

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