Meteorites:
95% of meteorites are stony or rocky meteorites
Of these, most are chondrites. These have chrondules, which
are small (~1 mm) inclusions that are 4.5 billion years old -- the oldest
known substances (that can be measured) in the Solar System.
The remaining 5% of meteorites are iron meteorties, like the
Canyon Diablo meteorite that hit here at Meteor Crater.
However, probably less than 5% of the parent bodies -- asteroids --
are iron bodies. This is because iron meteorites survive atmospheric
entry better than stony meteorites, and so are overrepresented in the
meteorite collection.
Tektites look like meteorites (they have a fusion crust from
atmospheric entry) but are not extraterrestrial materials (you
can measure their chemical compositions). Instead, they are pieces
of rock that are splashed up after an impact. They have
ballistic trajectories out of the atmosphere and back in.
The best place on Earth to collect meteorites is in
Antarctica.
65 million years ago a 10 km asteroid or comet hit in
what is now Mexico and wiped out the dinosaurs. Compare this
to the 50 meter object that hit here at Meteor Crater.
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