Researchers at the University of Gothenburg have identified traces of two enormous meteorite impacts in the county of Jämtland in central Sweden. One of the craters is enormous, while the other is a tenth its size.
The team announced the discovery in August, 2015. Researcher Erik Sturkell is Professor of Geophysics at the University of Gothenburg. He said:
The two meteorite impacts occurred at the same time, 458 million years ago, and formed these two craters.
Double impacts like this are very unusual. This is the first double impact on Earth that has been conclusively proved, say the researchers.
The research team found one of the craters 20 kilometers (12.4 miles) south of the city of Östersund. The enormous crater has a diameter of 7.5 kilometers (4.7 miles). The smaller crater, 16 kilometers (10 miles) away, has a diameter of 700 meters (.43 miles).
The two meteorite impacts 458 million years ago were not the only ones to strike Earth at that time. Sturkell said:
Around 470 million years ago, two large asteroids collided in the asteroid belt between Mars and Jupiter, and many fragments were thrown off in new orbits. Many of these crashed on Earth, such as these two in Jämtland.
At the time of the impacts, Jämtland was under the sea, with a water depth of 500 meters (.31 miles) at the points where two meteorites simultaneously struck. Sturkell said:
Information from drilling operations demonstrates that identical sequences are present in the two craters, and the sediment above the impact sequences is of the same age. In other words, these are simultaneous impacts.
The water was forced away during the impact, and for a hundred seconds these enormous pits were completely dry, say the researchers. Sturkell added:
The water then rushed back in, bringing with it fragments from the meteorites mixed with material that had been ejected during the explosion and with the gigantic wave that tore away parts of the sea bed.
Bottom line: University of Gothenburg researchers have identified traces of two enormous meteorite impacts in the county of Jämtland in central Sweden. The twin strike happened around 460 million years ago.