Tuesday, September 29, 2009

Meteor Crater Arizona

Meteor Crater ArizonaMeteor Crater is one of the youngest and best-preserved impact craters on Earth. The crater formed roughly 50,000 years ago when a 30-meter-wide, iron-rich meteor weighing 100,000 tons struck the Arizona desert at an estimated 20 kilometers per second.
High Resolution Image. The resulting explosion exceeded the combined force of today's nuclear arsenals and created a 1.1-kilometer-wide, 200-meter-deep crater.

Meteor Crater is a simple crater since it has no central peak or rim terraces. The crater formed in layered Paleozoic age sedimentary rocks, some of which are exposed in the nearby Grand Canyon. These rocks have been uplifted and in some cases overturned at the crater's raised rim. Debris sliding and subsequent erosion have partially filled the bottom of the crater with minor amounts of rim material and sediment.

The heavily cratered history of the Moon indicates that Earth also experienced many impact events early in its history. The processes of erosion and plate tectonics have combined to erase nearly all Earth's craters. To date, only about 150 impact craters have been identified on Earth, and most of those are severely eroded or buried by later rock units. The origin of this classic, simple meteorite impact crater was long the subject of controversy.

The discovery of fragments of the Canyon Diablo meteorite, including fragments within the breccia deposits that partially fill the structure, and a range of shock metamorphic features in the target sandstone proved its impact origin. Target rocks include Paleozoic carbonates and sandstones; these rocks were overturned just outside the rim during ejection. The hummocky deposits just beyond the rim are remnants of the ejecta blanket. This aerial view shows the dramatic expression of the crater in the arid landscape. The crater is named for Daniel Moreau Barringer, a mining entrepeneur who championed an impact origin for the crater early in the 20th.

Image Credit: D. Roddy (U.S. Geological Survey), Lunar and Planetary Institute. USGS-authored or produced data and information are considered to be in the U.S. public domain.

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Oblique aerial photograph looking northwest of Meteor Crater, Arizona; photo by David J. Roddy, USGS, Branch of Astrogeology. USGS Open-File Report 2005-1190, Figure 001. ID. Project Apollo (1960-1973) 001. pap00001

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