are pieces of stony or metallic material that reach the Earth from outer
space. They are mostly left-over
Achondrites are stony Meteorites that contain no chondrules.
Scientists believe that some of these meteorites originated on
the surface of the Moon or Mars, while others may have
originated on the Asteroids Vesta, Angelina, Nysa and others.
7.8 % of meteorites are achondrites. It has been suggested that
some angrites and enstatites could have originated on the
82% of all Meteorites are Chondrites: these contain
chondrules, and are therefore among the oldest rocks in the
Solar System. Chondrites contain varying amounts of nickel &
iron, and are generally attracted by a strong magnet. They may
display evidence of their fiery passage through the atmosphere
in the form of dark fusion crust and surface 'thumb-printing'
This is a slice of a Carbonaceous Chondrite, showing the
typical dark matrix, large chondrules, coloured clasts and
whitish calcium/aluminium inclusions of this type of stone.
Over a hundred amino acids (including eight of those found
in terrestrial life) have been identified in these meteorites,
causing many biologists to suggest that life may have been
'seeded' on Earth in this way!
Pallasites are widely believed to have originated at the core /
mantle boundary of small planets. They consist of a nickle-iron
matrix, in which are suspended crystalline fragments of
minerals such as olivine and pyroxine. Pallasites are very rare,
and make up around 1% of all falls.
The origin of Mesosiderite stony irons is, as yet, a mystery!
They consist of a stony matrix with varying amounts of metal
suspended randomly throughout. It is assumed that they were
formed during a massive impact between two well-differentiated
Iron meteorites make up around 5% of all falls. They largely
consist of Nickel and Iron with varying amounts of rarer metallic
elements such as Niobium and Iridium. When cut and polished,
irons often display the characteristic Widmanstatten pattern.
Earth, like all the planets and their satellites, was heavily
bombarded with meteorites and planetoids for a billion years
after the formation of the Solar System. This process has,
thankfully, slowed down, but massive impacts do still occur:
one such 65 million years ago probably hastened the extinction
of the Dinosaurs and drew the Mesozoic Era to an end!
Several hundred craters have been discovered on Earth: this
one is at Tenoumer in Mauritania.