Two impact craters near Östersund, Sweden were recently linked together and believed to have occurred simultaneously. This is the first time that geologists conclusively proved two impact craters formed at the same time.
The larger of the two craters is huge, spanning 4.7 miles wide. The smaller crater is located about 10 miles from the larger craters and is about half a mile wide. These impacts are believed to have occurred 458 million years ago during the Ordovician Period.
This dual impact occurred at a time in Earth's history when the rate of impacts were 100x higher than it is today. About 470 million years ago there was a large disruption in the asteroid belt between Mars and Jupiter. As a result, the Earth saw a two orders of magnitude increase in impact frequency. This period of increased impact frequency lasted millions of years and explains why there is a large number of Ordovician aged craters.
Geologists identified identical sequences within the two impact craters. In addition, the sediment above the impacts are of the same age.