Scientists have confirmed that the giant asteroid that hit Earth 66 million years ago and caused the extinction of the dinosaurs is not alone. In the same era, a second smaller space rock crashed into the sea off the coast of West Africa, creating a large crater. It was a "catastrophic event" that would trigger a tsunami at least 800 meters high that would sweep across the Atlantic.
Dr. Uisdean Nicholson of Heriot-Watt University first discovered Nadir Crater in 2022, but there is uncertainty about exactly how it formed. Now, Dr. Nicholson and his colleagues are convinced that the 9-kilometer-long depression was caused by an asteroid that crashed rapidly into the ocean floor.
They could not determine the exact date of the event, nor could they say whether it occurred before or after the asteroid, which left a 180-kilometer-wide Chikzuluble crater in Mexico. That asteroid ended the reign of the dinosaurs.
But they say the smaller rock also appeared at the end of the Cretaceous period, when the dinosaurs went extinct. When it crashes into the Earth's atmosphere, a fireball is formed.
"Imagine an asteroid hitting Glasgow and you're in Edinburgh, about 50 kilometers away. The fireball is about 24 times the size of the sun in the sky, enough to ignite the trees and plants of Edinburgh," Dr Nicholson said.
Before a tremor of magnitude 7 earthquake occurs, there is an extremely loud air explosion. A large amount of water may have left the seabed and subsequently flowed down, leaving a distinctive mark on the ground. Such a huge asteroid crashes into our Earth one after another in a short period of time, which is rare in the solar system. But researchers don't know why two asteroids hit Earth at the same time.
The asteroid that caused the Nadir crater is about 450-500 meters wide, and scientists believe it hit the Earth at a speed of about 72,000 km/h.
The closest humanity came to an event of this magnitude was the Tunguska explosion in 1908, when a 50-meter-long asteroid exploded over Siberia.
The Nadir asteroid is about the same size as Bennu, the most dangerous object currently orbiting near Earth.
According to the National Aeronautics and Space Administration (NASA) of the United States of United States, scientists believe the most likely date for Bennu to hit Earth is September 24, 2182. But that's still only a 1 in 2700 probability.
Never before in human history has there been an asteroid impact of this magnitude, and scientists can often only study images of eroded craters on Earth or craters on other planets.
To learn more about Nadir Crater, Dr. Nicholson and his team analyzed high-resolution 3D data provided by a geophysics company called TGS. Most of the craters have been eroded, but this one is well preserved, which means scientists can look further at the rock layers.
"This is the first time we've been able to see inside such an impact crater – it's really exciting," Dr Nicholson said, adding that there are only 20 ocean craters in the world, but none have been studied in detail like this.
研究结果发表在《自然-通讯-地球与环境》（Nature Communications Earth & Environment.）上。