Meteorites
Here we are dealing with meteorites - for meteors , which are something different, see Meteors.
Classification
- Stony about 90% stone, 10% iron and nickel
- Irons about 90% iron and nickel
- Stony-Irons
- Irons about 90% iron and nickel
About 90% of meteorites seen to fall are stones, but only about 25% of those actually found are of this type. Most meteorites recovered are iron meteorites.
They are composed of primitive material from the origin of Universe.
Their composition is of great similarity to the composition of asteroids.
Carbonaceous Chondrites
85% of stony meteorites are chondrites, so called because they contain spherical particles called chondrules. A subclass are the carbonaceous chondrites which contain organic componds. (Silly-Spelling warning - the 'h' in chondrules etc. is silent)
969 Murchison, Australia
List
| Weight | Current Location | ||
| Hoba West (Namibia) | 66 tonnes | still in place | |
| Ahnighito (Greenland) | 34 tonnes | American Museum of Natural History, New York | |
| Williamette (Oregon) | 14 tonnes | American Museum of Natural History | |
| Furnas County (Nebraska) | 1 tonne | University of New Mexico | |
| Paragould (Arkansas) | 400 kilos | Chicago Natural History Museum | |
Micrometeorites
Martian Meteorites
The so-called SNC meteorites are assumed to have come from Mars. Compared to 'ordinary' meteorites they
- young
- composed of volcanic rock whereas meteorites are usually unaltered primitive material
The arguments in favor of a Martian origin include
- Their isotopic content is compatible with Martian material
Martian meteorite ALH84001, found in Antartica.
In keeping up the best tradition of Martian canals, the War of the Worlds 'invasion' etc, the press entered a period of mass hysteria with ludicrous accounts about definite proof of life from a Martian meteorite.
Craters
There are known craters on Earth formed by meteor impact. The Barringer Crater, near Winslow in Arizona is about 1.5 kilometers across and 180 meters deep. Lake Bosumtwi has been formed by a collision (and, since then, achieved great religious significance by the Ashanti).
Most meteor craters are less obvious due to the effects of time.
Recently much excitement been caused by Chicxulub, in the Yucatan area of Mexico, a strong candidate for the impact crater of a meteor that caused the extinction of the dinosaurs.
