Researchers have found traces of two simultaneous meteorite impacts in the Swedish county of Jamtland - first evidence of a twin strike that occurred around 460 million years ago.
The researchers discovered two craters - while one is enormous with a diameter of 7.5 kilometres, the other, located 16 kilometres away, has a diametre of 700 metres - nearly one tenth of the size of the first.
"The two meteorite impacts occurred at the same time, 458 million years ago, and formed these two craters," said Erik Sturkell, professor of geophysics at University of Gothenburg.
The researchers explained that the two meteorite impacts 458 million years ago were not the only ones to strike Earth at this time but this is the first double impact on Earth that has been conclusively proved.
"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 Jamtland," Sturkell said in a statement released by University of Gothenburg on Friday.
Jamtland was under the sea at the time, with a water depth of 500 metres at the points where two meteorites simultaneously stuck.
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"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," Sturkell said.
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," Erik Sturkell pointed out.