It is not as famous as the Chicxulub crater, witness to the asteroid at the origin of the end of the dinosaurs, but it is just as impressive: the Vredefort crater or dome, from an area near present-day Johannesburg (South Africa), is the result of the collision of a celestial object on Earth, about two billion years ago. A huge impact, as it left behind a structure 250 kilometers in diameter, making it the largest impact crater on our planet. Previous research assumed that the rock responsible for its appearance was about 15 kilometers in diameter and moving at 15 kilometers per second. But a new study revises these estimates upwards.
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An asteroid over 20 kilometers in diameter
In a post by Journal of Geophysical Research September 2022, researchers from the University of Rochester (United States) claim that the asteroid could have been much larger and, at the same time, have had devastating consequences on the Earth’s environment. Estimating the size of the Vredefort crater at the time of the original impact has always been difficult, since two billion years of erosion have somewhat blurred its contours. Therefore, scientists relied on very accurate simulations of the fall of a celestial body and its impact.
If the asteroid had actually been 15 kilometers in diameter and moving at 15 kilometers per second, it should have produced a crater about 172 kilometers in diameter. This is a much smaller size than that estimated for the Vredefort crater, so potential measurements would be between 250 and 280 kilometers at the time of impact. The results of the simulations finally showed that the impactor must, to explain a crater of this size, be much larger: between 20 and 25 kilometers in diameter, and move at a speed of 15 to 20 kilometers per second.
Devastating effects on our planet
Larger than the asteroid that killed the dinosaurs 66 million years ago, the Vredefort asteroid could have been the cause of even more catastrophic global consequences. Increase in greenhouse gases and global temperature, widespread fires, acid rain, destruction of the ozone layer… The dust and aerosols emitted by the crash could even have blocked sunlight, subsequently cooling the earth’s surface. Miki Nakajima, assistant professor of earth and environmental sciences at the University of Rochester, explained in a statement:
Unlike the Chicxulub impact, the Vredefort impact left no traces of mass extinction or forest fires, since there were only single-celled life forms and no trees existed two billion years ago. However, the impact would have affected global climate potentially more broadly than the Chicxulub impact. This could have had a devastating effect on photosynthetic organisms.
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Information on the geological history of the Earth
The models used by the researchers also simulated how the asteroid’s material was ejected by the impact and how far it may have traveled. Previous investigations had already determined that it must have been launched in what is now the Karelia region of Russia. This recent research also shows that two billion years ago, the landmass Karelia was on was only 2,000-2,500 kilometers from the Vredefort crater, much closer than the two areas are today (nearly 10,000 kilometers). kilometres). Therefore, this work also helps to understand how landmasses may have moved over time.
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