Except for certain laboratory experiments and outdoor detonations of high explosives (including nuclear weapons), evidence of shock metamorphic conditions of extreme pressure and heat on Earth exist only within and around impact craters. Only hypervelocity impact between objects of substantial size moving at cosmic velocity (at least several kilometers per second) can produce these conditions. Meteorites larger than approximately 246 ft (75 m) in diameter, asteroids, and comets can pass through Earth's atmosphere and yet retain a very high percentage of their original velocity. In such events, this energy of motion is converted into seismic and heat energy almost instantaneously. On planetary bodies with no atmosphere, even smaller impacting bodies (even micrometeorites) can produce shock metamorphic effects. Meteorites recovered on Earth, which are fragments of larger bodies shattered by impact elsewhere in the solar system, also show shock metamorphic features and effects.

Shock metamorphism involves changes wrought by...