A team of scientists from the University of Gothenburg, Sweden, has found traces of two meteorite impacts in the Swedish county of Jämtland, a twin strike that occurred 458 million years ago (Ordovician period).
Artist’s conception of two meteorites striking Earth. Image credit: Don Dixon / Erik Sturkell / University of Gothenburg.
Prof Erik Sturkell from the University of Gothenburg’s Department of Earth Sciences and his colleagues found one of the craters 12 miles (20 km) south of the city of Östersund. This is an enormous crater, with a diameter of 4.7 miles (7.5 km).
The second, smaller crater is located 10 miles (16 km) from there, and has a diameter of 2,300 feet (0.7 km).
“Two meteorite impacts occurred at the same time, 458 million years ago, and formed these two craters,” Prof Sturkell said.
“From studies of meteorites, we know that a large disruption of an asteroid occurred around 470 million years ago in the asteroid belt between Mars and Jupiter,” he and his colleagues explained.
“This disruption spawned large amounts of asteroid debris and dust, some of which entered Earth-crossing orbits, resulting in an increase of two orders of magnitude in the influx of smaller fragments to Earth; the influx lasted for a couple of million years.”
“It is assumed that the disruption also resulted in the delivery of larger asteroid fragments to Earth that were responsible for the relatively high number of Ordovician craters.”
According to the team, the Jämtland region was under the sea at the time, with a water depth of 1,640 feet (0.5 km) at the points where two meteorites simultaneously stuck.
“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,” Prof Sturkell explained.
“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.
“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,” he said.
“This is the first double impact on Earth that has been conclusively proved,” the scientists said.
Source link: https://www.sci.news/geology/science-ordovician-impact-craters-sweden-03231.html
