Meteorite
A meteorite isrelatively small extraterrestrial material body that reachesEarth's surface. Whilespace these bodiescalled meteoroids ("small" asteroids, approximately boulder-sized or less, whichgenerally fragments resulting fromcollisiontwo, or more, asteroids). Upon enteringatmosphere air dragfriction will causebodyheat up, emitting light, thus formingmeteor, fireball, or shooting star.
Most meteors disintegrate inair, making impact events (Earth impacts) onsurfaceEarth uncommon. About 500 baseball sized rocksyear reachsurface. Large meteorites may strikegroundconsiderable force, leaving behindmeteor crater. The kindcrater will depend onsize, composition, degreefragmentation,incoming angle ofmeteor. The forcecollisionEarth's surface may cause widespread destruction. Occasional damageproperty, livestockeven people has been recordedhistoric times. Incasecomet fragments, whichlargely composedice,considerable concussion may occur even though no fragment oforiginal meteoroid survives;famed Tunguska eventthoughtresult from such an incident.
79%meteoritesChondrites - ballsmafic mineralssmall grain size indicativerapid cooling. In most chondrites small spherules, called chondrules, can be found. Chondritestypically about 4.6 billion years old andthoughtrepresent material fromasteroid belt. Itunknown howformed. Carbonaceous Chondrites constitute about 5%meteoritescontain small amountsorganic materials including amino acids. Also presolar grainsidentifiedcarbonaceous chondrites. The isotope ratiosCarbonaceous Chondritessimilarthose ofsun. Carbonaceous chondritesthoughtbe unaltered solar nebula material.
Achondritessimilarterrestrial mafic igneous rockssometimesbrecciated. Achondritesabout 8% ofincoming material andthoughtrepresent crustal materiallarger asteroids. About 6%meteoritesIron meteoritesintergrowthsiron-nickel alloys, such as kamacite. Unlike chondrites,crystalslargeappearrepresent slow crystallization. Iron meteoritesthoughtbecore materialone or more planets that subsequently broke up. Stony iron meteorites constituteremaining 2%. They aremixtureiron-nickelsilicate minerals. Theythoughthave originated inboundary zone abovecore regions where Iron meteorites originated. A small numbermeteorites belongadditional groups or subgroupsunique chemical characteristics relativeother members oflarger groups. For example, Lunar meteorites or Martian meteorites.
One theory stipulates thatlarge meteorite impact causedmass extinction ofdinosaurs, as well as other mass extinction events throughouthistory ofearth.
See Siljanother notable meteorite impacts. See comet, asteroid, Leonids, Geminidssolar systemmore information on extraterrestrial bodies.
The only recorded fatality from meteorite impactsan Egyptian dog, who was killed1911. The causedeath was identified in1980s as beingMartian meterorite. The first,as2003, only known modern case ofhuman being hit byspace rock occurred on November 30, 1954Sylacauga, Alabama. There an 8.5 pound sulfide meteorite crashed throughroofhitMrs. Elizabeth Hodgesher living room afterbounced off her radio. Other thannasty bruise she was OK.
See also: Impact event, Tunguska event, asteroid
