Meteorites and such from Mars

What we call meteorites are fragments broken off from other celestial bodies after their fall on Earth. A coarse classification divides meteorites according to their composition: stony meteorites (by far most abundant), iron meteorites and stony-iron meteorites. Before they fall to Earth, during their journey in interplanetary space (usually some million years for stony meteorites, several hundred million years for iron meteorites) these fragments are called meteoroids.

"Hot deserts" (e.g., Sahara) and "cold deserts (as Antarctica) are important areas, where meteorites are found, because of the slow weathering in dry climates.

 Parent bodies of most meteorites are the asteroids, the minor planets in the asteroid belt between planets Mars and Jupiter. The meteoroid fragments are liberated during collisions. A small number of meteorites, however, as has been found about thirty years ago, represent fragments from the Moon and from Mars. Some very primitive meteorites may derive from comets.

Impacts of larger fragments or of whole asteroids or comets are a danger for life on Earth (e.g., the extinction of the dinosaurs 65 million years ago).

Meteorites from Mars

By now we know more than 30 meteorites that seem to come from planet Mars. Among them is the meteorite ALH84001, which was found in Antarctica in 1984, and which became famous, because some researchers believe it shows signs of former life on Mars. The other Martian meteorites belong to the groups of shergottites, nakhlites and chassignites, commonly abbreviated SNC meteorites.

Main arguments for a Martian origin
a) ages of “only” 1.3 billion years, or less, i.e. they are much younger than common meteorites with an age of ca. 4.5 billion years (exception: ALH84001, which is older).
b) the discovery of noble gases in some of them, which in their composition agree with that measured by the Viking lander for the Martian atmosphere  (within the rather large uncertainties of the Viking measurements).