impacts - Meteroites Impacts Mass Extinction EENS 204...

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This document last updated on 23-Apr-2004 EENS 204 Natural Disasters Tulane University Prof. Stephen A. Nelson Meteorites, Impacts, and Mass Extinction Meteorites A Meteorite is a piece of rock from outer space that strikes the surface of the Earth. A Meteoroid is a meteorite before it hits the surface of the Earth. Meteors are glowing fragments of rock matter from outside the Earth's atmosphere that burn and glow upon entering the Earth's atmosphere. They are more commonly known as shooting stars. Some meteors, particularly larger ones, may survive passage through the atmosphere to become meteorites, but most are small objects that burn up completely in the atmosphere. They are not, in reality, shooting stars. Fireballs are very bright meteors. Meteor Showers - During certain times of the year, the Earth's orbit passes through a belt of high concentration of cosmic dust and other particles, and many meteors are observed. The Perseid Shower, results from passage through one of these belts every year in mid-August, and Leonid shower occurs in mid-November. Throughout history there have been reports of stones falling from the sky, but the scientific community did not recognize the extraterrestrial origin of meteorites until the 1700s. Within recent history meteorites have even hit humans- z 1938 - a small meteorite crashed through the roof of a garage in Illinois z 1954 - A 5kg meteorite fell through the roof of a house in Alabama. z 1992 - A small meteorite demolished a car near New York City. z 2003 - A 20 kg meteorite crashed through a 2 story house in uptown New Orleans z 2003 - A shower of meteorites destroys several houses and injures 20 people in India Meteorite fragments have been found all over the surface of the Earth, although most have been found in Antarctica. In Antarctica they are easily seen on the snow covered surface or embedded in ice. The fall of meteorites to the Earth's surface is part of the continuing process of accretion of the Earth from the dust and rock of space. When these rock fragments come close enough to the Earth to be attracted by its gravity they may fall to the Earth to become part of it. As we will Meteroites, Impacts, & Mass Extinction 4/23/2004 Page 1 of 13
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see the evolution of life on the Earth has likely been affected by collisions with these space objects, and collisions could affect the Earth in the future as well. Composition and Classification of Meteorites Meteorites can be classified generally into three types: z Stones - Stony meteorites resemble rocks found on and within the Earth. They are the most common type of meteorite, although because they resemble Earth rocks they are not commonly recognized as meteorites unless someone actually witnesses their fall. Stony meteorites are composed mainly of the minerals olivine, and pyroxene. Some have a composition that is roughly equivalent to the Earth's mantle. Two types are recognized: { Chondrites - Chondrites are the most common type of stony meteorite. They are composed of small round glassy looking spheres, called chondrules, that likely
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