Sedimentary rocks of the type that rim Meteor Crater are deposited, naturally, with younger rocks above resting on older ones below. Yet at Meteor Crater, Shoemaker found just the opposite: The rocks on the crater rim were actually upside down geologically, with younger underneath older. He concluded that they had been blasted into the air, flipped over, and then had fallen to the earth again, but still upside down, forming a kind of upside-down layer cake. To lift huge masses of rocks and turn them over would have taken a great deal of energy. He too found the crater floor filled with breccia. Comparison with craters produced by nuclear test explosions allowed him to calculate that Meteor Crater had been formed by an iron meteorite weighing 60,000 tons, measuring 25 m in diameter, and traveling at '5 km/sec. Shoemaker calculated that the explosion was equivalent to the detonation of a '.7 megaton nuclear device (85 times the magnitude of the bomb dropped on Hiroshima; recent estimates are higher) and destroyed all of the impactor save a few fragments. In '964, the old generation and the new came together when Shoemaker guided Walter Bucher on a field trip to Meteor Crater. The evidence apparently convinced Bucher that the crater after all was due to impact, but he died before he could make his change of heart known.'3
Was this article helpful?