How Meteor Impacts formed the Earth - A look inside the Barringer Meteor Crater in Arizona
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A look at how asteroids played a role in the formation of the Earth; a study of how the Barringer Meteor Crater in Arizona was formed, and why little evidence remains of the meteor itself that created it. Meteor Crater is a meteorite impact crater approximately 43 miles (69 km) east of Flagstaff, near Winslow in the northern Arizona desert of the United States. It is the largest impact crater yet discovered in the United States. Because the United States Board on Geographic Names commonly recognizes names of natural features derived from the nearest post office, the feature acquired the name of "Meteor Crater" from the nearby post office named Meteor. The site was formerly known as the Canyon Diablo Crater, and fragments of the meteorite are officially called the Canyon Diablo Meteorite. Scientists refer to the crater as Barringer Crater in honor of Daniel Barringer, who was first to suggest that it was produced by meteorite impact. The crater is privately owned by the Barringer family through their Barringer Crater Company, which proclaims it to be "best preserved meteorite crater on Earth". Despite its importance as a geological site, the crater is not protected as a national monument, a status that would require federal ownership. It was designated a National Natural Landmark in November 1967. Meteor Crater lies at an elevation of about 1,740 m (5,710 ft) above sea level. It is about 1,200 m (3,900 ft) in diameter, some 170 m deep (570 ft), and is surrounded by a rim that rises 45 m (148 ft) above the surrounding plains. The center of the crater is filled with 210--240 m (690--790 ft) of rubble lying above crater bedrock. One of the interesting features of the crater is its squared-off outline, believed to be caused by pre-existing regional jointing (cracks) in the strata at the impact site. The crater was created about 50,000 years ago during the Pleistocene epoch when the local climate on the Colorado Plateau was much cooler and damper. It is the world's best preserved meteorite impact site. At the time, the area was an open grassland dotted with woodlands inhabited by woolly mammoths and giant ground sloths. It was probably not inhabited by humans; the earliest confirmed record of human habitation in the Americas dates from long after this impact. The object that excavated the crater was a nickel--iron meteorite about 50 meters (55 yards) across, which struck the plain at a speed of several kilometers per second. Impact energy has been estimated at about 10 megatons. The speed of the impact has been a subject of some debate. Modeling initially suggested that the meteorite struck at a speed of up to 20 kilometers per second (45,000 mph), but more recent research suggests the impact was substantially slower, at 12.8 kilometers per second (28,600 mph). It is believed that about half of the impactor's bulk was vaporized during its descent before it hit the ground. The meteorite itself was mostly vaporized upon impact, leaving little in the crater. The crater came to the attention of scientists following its discovery by European settlers in the 19th century. Dubbed the Canyon Diablo crater -- from Canyon Diablo, Arizona, the closest community to the crater in the late 19th century, 12 miles (19 km) northwest of the crater, but now a ghost town -- it had initially been ascribed to the actions of a volcano. This was not an unreasonable assumption, as the San Francisco volcanic field lies only about 40 miles (64 km) to the west.