File:Meteor Crater, Arizona Mining Site.jpg
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DescriptionMeteor Crater, Arizona Mining Site.jpg |
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. In 1891 Grove Karl Gilbert, chief geologist for the U.S. Geological Survey, investigated the crater and concluded that it was the result of a volcanic steam explosion. Gilbert had assumed that if it were an impact crater then the volume of the crater, as well as meteoritic material, should be present on the rim. Gilbert also assumed a large portion of the meteorite should be buried in the crater and that this would generate a large magnetic anomaly. Gilbert's calculations showed that the volume of the crater and the debris on the rim were roughly equivalent, so that the mass of the hypothetical impactor was missing. Further there were no magnetic anomalies. Gilbert argued that the meteorite fragments found on the rim were coincidental. Gilbert would publicize these conclusions in a series of lectures in 1895. In 1892 Gilbert would be among the first to propose that the moon's craters were caused by impact rather than volcanism. In 1903, mining engineer and businessman Daniel M. Barringer suggested that the crater had been produced by the impact of a large iron-metallic meteorite. Barringer's company, the Standard Iron Company, received a patent signed by Theodore Roosevelt for 640 acres (2.6 km2) around the center of the crater in 1903. The claim was divided into four quadrants coming from the center clockwise from northwest named Venus, Mars, Jupiter and Saturn. In 1906 Roosevelt authorized the establishment of a newly named Meteor, Arizona post office (the closest post office before was 30 miles (48 km) away in Winslow, Arizona). Standard Iron Company conducted research on the crater's origins between 1903 and 1905. It concluded that the crater had indeed been caused by an impact. Barringer and his partner, the mathematician and physicist Benjamin Chew Tilghman, documented evidence for the impact theory in papers presented to the U.S. Geological Survey in 1906 and published in the Proceedings of the Academy of Natural Sciences in Philadelphia. Barringer's arguments were met with skepticism, as there was a reluctance at the time to consider the role of meteorites in terrestrial geology. He persisted and sought to bolster his theory by locating the remains of the meteorite. At the time of first discovery by Europeans, the surrounding plains were covered with about 30 tons of large oxidized iron meteorite fragments. This led Barringer to believe that the bulk of the impactor could still be found under the crater floor. Impact physics was poorly understood at the time and Barringer was unaware that most of the meteorite vaporized on impact. He spent 27 years trying to locate a large deposit of meteoric iron, and drilled to a depth of 419 m (1,376 ft), but no significant deposit was ever found. Barringer, who in 1894 was one of the investors who made $15 million in the Commonwealth silver mine in Pearce, Arizona in Cochise County, Arizona, had ambitious plans for the iron ore. He estimated from the size of the crater that the meteorite had a mass of 100 million tons. The current estimate of 300,000 tons for the impactor is only three-tenths of one percent of Barringer's estimate. Iron ore of the type found at the crater was valued at the time at $125/ton so Barringer believed he was searching for lode worth more than a billion 1903 dollars. Despite Barringer's findings and other excavations in the early 20th century, geologists' skepticism continued until the 1950s when planetary science gained in maturity and understanding of cratering processes increased. Professor Herman Leroy Fairchild, an early promoter of impact cratering, argued Barringer's case in an article in Science in 1930. It was not until 1960 that later research by Eugene Merle Shoemaker would confirm Barringer's hypothesis. The key discovery was the presence in the crater of the mineral stishovite, a rare form of silica found only where quartz-bearing rocks have been severely shocked by an instantaneous overpressure. It cannot be created by volcanic action; the only known mechanism of creating it is through an impact event (or artificially through a nuclear explosion). Shoemaker's discovery is considered the first definitive proof of an extraterrestrial impact on the Earth's surface. Since then, numerous impact craters have been identified around the world, though Meteor Crater remains one of the most visually impressive due to its size, young age and lack of vegetation cover. On August 8, 1964, a pair of commercial pilots in a Cessna 150 flew low over the crater. On crossing the rim, they could not maintain level flight. The pilot attempted to build up speed by circling in the crater to climb over the rim. During the attempted climb out, the aircraft stalled, crashed, and caught fire. It is commonly reported that the plane ran out out of fuel, but this is incorrect. Both occupants were severely injured but survived their ordeal. A small portion of the wreckage not removed from the crash site remains visible to this day. |
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Source | Flickr: Meteor Crater, Arizona Mining Site | ||
Author | Ken Lund | ||
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot A540 |
Exposure time | 1/100 sec (0.01) |
F-number | f/4 |
Date and time of data generation | 15:34, 17 December 2010 |
Lens focal length | 5.8 mm |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | picnik.com |
File change date and time | 15:34, 17 December 2010 |
Y and C positioning | Centered |
Exif version | 2.2 |
Date and time of digitizing | 15:34, 17 December 2010 |
APEX shutter speed | 6.6582115219261 |
APEX aperture | 4 |
Maximum land aperture | 2.757023255814 APEX (f/2.6) |
Metering mode | Pattern |
Flash | Flash did not fire, compulsory flash suppression, red-eye reduction mode |
Color space | sRGB |
Focal plane X resolution | 12,515.555555556 |
Focal plane Y resolution | 12,497.041420118 |
Focal plane resolution unit | inches |
Sensing method | One-chip color area sensor |
Custom image processing | Normal process |
Exposure mode | Manual exposure |
White balance | Manual white balance |
Digital zoom ratio | 1 |
Scene capture type | Landscape |