Over its history, Earth has been bombarded by countless rocks from outer space. The weathering action of wind and water has erased most of the scars, but in a few places, pristine craters are a sobering reminder of the destructive power of such an impact.
One of the most well-preserved is Meteor Crater, also known as Barringer Crater, in northern Arizona. 50,000 years ago, an iron-nickel meteorite 150 feet in diameter, traveling 40,000 miles per hour, struck the Earth here. The impact released more energy than 20 million tons of TNT and left a crater almost a mile wide. The crater's young age (on the geologic time scale), plus the dry desert climate, have left it relatively intact. This photo was taken from the crater's rim, as a guide explains the crater's history to a tour group.
Originally suspected to be of volcanic origin, Barringer Crater was proven to be an impact crater by Gene Shoemaker of the United States Geological Survey. He was also instrumental in training the Apollo astronauts on this site in preparation for the moon landings. Shoemaker was killed in a car crash in 1997, while on an expedition to study impact craters in Australia. His fascinating career is detailed in the biography Shoemaker by Levy: The Man Who Made an Impact by David H. Levy.
This photograph appeared on NASA/USRA's Earth Science Picture of the Day site on June 26, 2001.