sudbury-basin.jpg1416332955.cfThe Sudbury Basin, which is the world’s second-largest impact crater, was likely formed by an enormous comet that battered Earth more than 1.8 billion years ago, new research suggests.  The findings settle a long-standing mystery about how the giant hole in the Earth formed.  The Sudbury Basin is a roughly elliptical crater that measures about 37 miles by 18 miles (60 kilometers by 30 kilometers), located on the outskirts of Sudbury, Ontario, in Canada. Ever since miners discovered rich deposits of copper, nickel, palladium and other valuable metals there in the 1880s, scientists have wondered how the giant hole in the Earth came into existence, said study co-author Joseph Petrus, an earth sciences doctoral candidate at Laurentian University in Sudbury. Scientists knew an impact caused the crater because of characteristic “shock features,” such as rock fragments cemented together and shatter cones, or a conical, repeating structure of striations in the rock. More