A second meteorite could ‘finish off’ the dinosaurs

A team of researchers from various institutions and led by Hugh Nicholson, from Heriot-Watt University in Edinburgh, has just located what appears to be a 9 km diameter impact crater buried under the seafloor off the coast of West Africa. According to a study published in Science Advances, the crater fits an asteroid about 400m in diameter. The impact occurred at the same time that another much larger meteorite, about 13 km, made landfall in the bay of Chicxulub and ended the reign of the dinosaurs. The researchers speculate that the new meteorite was a fragment of the one that caused the fifth great mass extinction of life on Earth 66 million years ago.

Nicholson and his colleagues detected the possible crater in seismic reflection data obtained during an oil survey in the area. Named Nadir Crater after a nearby seamount, the impact site is on the continental shelf just a few hundred kilometers off the coast of Guinea, buried under some 300 meters of sediment and in an area where the ocean is 900 meters deep. meters.

As explained in the study, the detected structure has all the characteristics of an impact crater, including a raised rim and signs of material ejected out of the crater itself. The modeling, done by Veronica Brayfrom the University of Arizona in Tucson and co-author of the article, suggests that it was caused by the impact of an asteroid about 400 meters in diameter.

“Definitely – says Uisdean Nicholson – what we have found fits perfectly with an impact crater.”

At the same time as Chicxulub

The Nadir crater appears to have formed about 66 million years ago, at the same time as the Chicxulub crater (180 kilometers across) in what is now the Gulf of Mexico. That temporal coincidence has led the team to speculate that the new African crater was made by a fragment that broke off from the Chicxulub asteroid itself.

If the breakup of the large asteroid had occurred just before impact, the researchers say, the two craters would be in close proximity. Instead, Nicholson suggests that gravity could have broken the asteroid apart during a previous orbit that passed close to Earth, causing two impacts a few days apart. Something similar to what happened with the cometa Shoemaker-Levywhich in 1992 broke into 21 fragments that two years later, and for six days, hit Jupiter.

looking for more craters

According to Nicholson, it is possible that the Chicxulub asteroid also broke into several pieces, which implies that several craters associated with that disastrous event remain to be discovered. The reasons for not having found them are several: these craters could have been ‘erased’ by erosion or by tectonic processes; or they might not have formed at all if some of the fragments fell into deep water, several km deep.

Of course, there is also the possibility that the two events are unrelated to each other, something that Nicholson himself contemplates. For this reason, together with his team, he has presented a proposal to drill the Nadir crater and recover materials that could confirm if it is definitely an impact structure, in addition to dating the event with much greater precision.

According to the researchers, the Nadir impact, by itself, could not have triggered a mass extinction event, although it would have had serious effects on the surrounding region, with tsunamis up to 500 meters high. In Nicholson’s words, “it would have been a very important regional event.”

What the asteroid would have done is slightly increase the global temperature, since it released carbon from the rocks against which it impacted and destabilized the methane hydrates on the seabed.

The Chicxulub impact was about 1,000 times more powerful and it was enough to cover the entire planet with dust in just a few hours, causing the disappearance of 75% of all living species at that time. But off the coast of Africa, the Nadir would have been enough to reinforce the destructive effects of that large impact, accelerating the destruction process.

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