Meteorites
Meteoroid
- a solid small body in space. When it enters the atmosphere at between 10 and 70 km/sec it becomes a:Meteor
– A shooting star, at heights of 80 to 110 kilometers above Earth's surface. If it makes it to the surface it becomes a:Meteorite
- the fragment found on EarthHundreds of tons of meteoroids enter the Earth's atmosphere each day.
Major Meteorite Types
|
Type |
Sub-type |
Abundance (total %) |
Composition |
|
Stony Meteorites |
|
94 |
|
|
|
Carbonaceous Chondrites |
4 |
Carbon- and volatile-rich undifferentiated |
|
|
Ordinary Chondrites |
82 |
Metamorphosed chondrites |
|
|
Achondrites |
8 |
Igneous textures, differentiated |
|
Stony-Iron Meteorites |
|
1 |
Silicate-metal mixtures, differentiated |
|
Iron Meteorites |
|
5 |
Silicate-metal mixtures, differentiated |
Meteorites are rocky or metallic bodies that reach Earth from space. Many have originated from asteroids.
Chondrites contain chondrules
, which are quickly cooled, once molten millimeter-sized droplets of material in the nebula.Carbonaceous chondrites
, have the highest proportions of volatile elements, representing the most primitive material left.Carbonaceous chondrites composition is similar to that of the Sun
(minus H, He and a few others).Ordinary Chondrites
are sligthly ‘cooked’ chondrites.Achondrites resulted from melting
either through impacts or internal fractionation of the parent body.Iron, and stony-iron meteorites are the result of differentiation
of the parent body.Has any human ever been killed by a meteorite?
Old Chinese records indicate that people have been killed by falling meteorites, but there is no record of meteorite deaths in modern times.
Elizabeth Hodges, of Sylacauga, Alabama, was given a terrible bruise on the side by a falling meteorite in 1954.
A young boy was struck in the head by a meteorite that had been slowed down by the leaves of a banana plant in Uganda in 1992.
The Nakhla meteorite killed a dog when it fell in Egypt in 1911.
On the other hand …
Earth Extinctions from Space
Cretaceous-Tertiary - 65 million years ago
Most likely
caused by impact of several-mile-wide asteroid that created the Chicxulub crater now hidden on the Yucatan Peninsula and beneath the Gulf of Mexico. This extinction killed 16 percent of marine families, 47 percent of marine genera and 18 percent of land vertebrate families, including of course the dinosaurs. The worldwide geological formations marking the Cretaceous-Tertiary boundary are enriched with iridium, thought to have been derived from the impactor.Permian-Triassic extinction - 251 million years ago
The Permian-Triassic extinction (the mother of all extinctions to borrow much overused cliche)
killed 95 percent of all species, 53 percent of marine families, 84 percent of marine genera and an estimated 70 percent of land species such as plants, insects and vertebrate animals. Recent evidence suggests that it too was caused by the impact of an asteroid of comet.The scientists do not know the site of the impact 250 million years ago, when all Earth's land formed a supercontinent called Pangea. The evidence in this case is the presence of complex carbon molecules called buckminsterfullerenes, or Buckyballs, with the noble (or chemically nonreactive) gases helium and argon trapped inside their cage structures.These particular Buckyballs are extraterrestrial because the noble gases trapped inside have an unusual ratio of isotopes which could only have formed in carbon stars. The gas-laden fullerenes were formed outside the Solar System, and their concentration at the Permian-Triassic boundary means they were delivered by a comet or asteroid estimated at 6 -12 km across.