METEOR CRATER, ARIZONA
0.75-Mile-Wide Meteor Impact Crater
50,000 Years Ago
It is best described as a giant bowl surrounded by a raised rim. It is three-quarters of a mile in diameter and the center of the bowl is six hundred feet below the level of the surrounding plain. It was the simplicity of form, and how the crater suddenly disrupted a flat desert landscape, that puzzled people. Adding to the confusion, tons of meteoric iron, mostly in the form of small fragments, had been found lying on the Palin immediately surrounding crater.
Exterior view of the raised rim of Meteor Crater.
Throughout the first half of the twentieth century, the prevailing opinion was that it formed by a rare type of volcanic explosion, an explosion that did not produce any type of volcanic rock, but had produced a huge circular crater.
Then geologic Eugene Shoemaker began to study the crater. The crucial observation came in the 1960s when two high-pressure forms of silicate—coesite and stishovite—were found at the crater. And there was only one natural process that could produce pressures high enough to produce coesite and stishovite: a meteor impact.
Interior view of the bowl shape of Meteor Crater.
Today there are 200 features on the Earth that have been confirmed, mainly through the identification of high-pressure minerals, such as coesite and stishovite, to be the result of meteor impacts. A meteor impact crater defines the entrance to Chesapeake Bay and another (Middlesboro Crater, Kentucky) is responsible for the highly eroded rocks that caused the Cumberland Gap to form. Mont des Eboulements in the Charlevoix region of Quebec is the central rebound of the Earth's crust following the moments of a meteor impact about 350 million years ago. Ninety percent of the people of Charlevoix live within this impact feature.