view from rim of Meteor Crater
Standing on the rim of Meteor Crater gives you a better idea of its size. The rim on the far side is over a kilometer away and the floor is over 160 meters below the rim. For another sense of the scale, the people on the far left edge of the picture could be one of more than two million people seated along the crater's sloping sides watching twenty American football games going on simultaneously on the crater floor! If you click on the picture, a full-resolution version (2635 x 484) will appear.

Meteor Crater was created about 50,000 years ago when a iron-nickel meteorite about 45 meters across slammed into the plains of northern Arizona with an explosive energy of more than 20 megatons of TNT. Although there was speculation as far back as 1891 that the crater was made by a meteorite impact, it was not until 1960 that the impact origin was proved correct by Eugene Shoemaker. His team from the U.S. Geological Survey found high-pressure forms of silica called coesite and stishovite. They are formed when silicon dioxide is subjected to pressures more than 20,000 times atmospheric pressure. In nature, such pressures happen only in impacts.

Some other criteria for showing a feature has an impact origin are: nickel-iron specimens in the surrounding area (if the meteorite was an iron or stoney-iron type), a raised and folded rim (lower rock layers lifted up and over upper rock layers; Meteor Crater's rim is 45 meters above the surrounding plain), breccia lens (lens-shaped mass of rock fragments violently broken apart and recemented together), shattercones, shock micro-deformation of quartz, impact glasses, shale balls, shock melted rock, and rock flour.

Meteor Crater is a simple crater type---small craters with smooth, bowl-shaped interiors. Larger craters, called complex craters, have a central peak and terraced inner walls. On the Earth, the transition to complex crater type occurs for craters above about three kilometers in diameter. On smaller bodies with less gravity, the transition occurs at larger crater diameters, e.g., 60 kilometers on the Moon. At larger diameters (100 to 300 kilometers on the Moon, Mars, and Mercury) the central peak widens and turns into a ring. The largest craters (over several hundred kilomters in diameter) have several concentric rings and are called multi-ring basins.

More about impact cratering on the Earth

Back to Effects of Asteroid Impact on Earth section

last update: June 2, 2007

Is this page a copy of Strobel's Astronomy Notes?

Author of original content: Nick Strobel