Earth has over 200 large
craters or astroblemes.
When a large meteoroid
enters Earth's atmosphere, it's traveling at about 10 miles per
second. It usually breaks up into several pieces in
flight. At the moment of impact, a massive shock wave is sent
downward into the rock and upward into the meteorite. The rock
is now impacted into less than half of the original size.
After the initial shock wave, an explosion caused by a decompression
wave throws rock outward onto the rim and surrounding area.
Most of the meteorite vaporizes in the explosion and throws tiny
metal spheroids and fragments outward to the surrounding area.
The main mass of the meteorite is reduced to spheroids. There
is a large dust cloud caused by the impact which rains rock and
meteorite dust over the crater.
If no meteorite material
is found, the crater was formed by a comet. Comets are
basically giant snowballs.