The huge asteroid that hit the Earth and wiped out the dinosaurs 66 million years ago was not the only celestial body that hit the planet then, scientists have confirmed.
A second, smaller space rock hit the sea off the coast of West Africa, creating a large crater.
It was a "catastrophic event", say scientists, which could have caused a tsunami, at least 800 meters high.
Juzdin Nikolson from Heriot-Vot University was the first to find the Nadir crater in 2022, but it is still not known how it actually formed.
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Nicholson and his colleagues are sure that the basin, nine kilometers deep, was created by a rock that fell into the seabed.
They cannot determine exactly when the impact occurred, or whether the crack was created before or after the fall of the asteroid that had previously created a crater more than 180 kilometers in diameter near Chicxulub in the Yucatan, which ended the reign of the dinosaurs.
They claim that at the end of the dinosaur era, a smaller rock fell and probably formed a fireball upon impact.
"Imagine an asteroid hitting Glasgow and you're 50 kilometers away in Edinburgh.
"The fireball is believed to have been about 24 times the size of the Sun in the sky, enough to set fire to trees and plants in Edinburgh," says Nicholson.
It was probably followed by an extremely strong air explosion, which was followed by a seismic tremor like an earthquake with a magnitude of seven on the Richter scale.
It is assumed that huge amounts of water retreated from the seabed and then returned, creating unique imprints on the earth's surface.
It is unusual for such large asteroids from our solar system to hit Earth in such a short time, but researchers do not know why these two celestial bodies hit the planet, following each other.
The asteroid that created the Nadir crater was about 450-500 meters wide, and scientists think it hit the Earth at a speed of about 72.000 kilometers per hour.
The closest event to this is from 1908, when a 50-meter-long asteroid exploded in the sky over Siberia in Russia.
Asteroid Nadir was about the size of Bennu, currently the most dangerous near-Earth object.
Bennu could most likely hit our planet on September 24, 2182, according to the American Space Agency (NASA), but the chances of that happening are still one in 2.700.
The planet has never been hit by an asteroid of that size before, so scientists have to study eroded craters on Earth or images of craters on other planets.
To better understand Crater Nadir, Nicholson and his team analyzed high-resolution 3D data from geophysics company TGS.
Most of the craters have disintegrated over time, but Nadir is well-preserved, meaning scientists can reach different levels of rock.
"This is the first time we've been able to see the inside of a crater like this - it's really exciting," says Dr Nicholson.
There are only 20 Mork craters in the world, but none have been studied in detail like this one, he adds.
The results were published in the journal Nature Communications Earth & Environment.
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