When comet Shoemaker-Levy 9 collided with Jupiter in 1994, the planet's strong gravitational pull broke it into pieces that produced a dramatic string of impacts. Researchers had not believed that Earth's gravity was strong enough to produce a similar event. Canadian scientists, however, have now identified a chain of five impact craters, including Manicouagan and St. Martin in Canada and Red Wing in the United States, stretching over 2,400 miles, that they believe were produced by such an event.
John G. Spray and his colleagues at the University of New Brunswick identified five craters, each about 214 million years old. When they accounted for movement of tectonic plates on the Earth's surface, they found that the craters were aligned across Europe and North America.
Compiled by Times medical writer Thomas H. Maugh II