Meteoritic impacts, shock waves

Shock waves can be natural in origin, for example, lightning, volcanic explosions or meteorite impacts. But human activity can also generate shock waves, for example in chemical or nuclear explosions. On the positive side, shock waves can reduce human suffering when used in shock wave lithotripsy (a method for fragmentation of kidney stones and gallstones). 

The question of the stability of the biomolecules is a vital one. Could they really have survived the tremendous energies which would have been set free (in the form of shock waves and/or heat) on the impact of a meteorite Blank et al. (2000) developed a special technique to try and answer this question. They used an 80-mm cannon to produce the shock waves the shocked solution contained the two amino acids lysine and norvaline, which had been found in the Murchison meteorite. Small amounts of the amino acids survived the bombardment , lysine seeming to be a little more robust. In other experiments, the amino acids aminobutyric acid, proline and phenylalanine were subjected to shock waves the first of the three was most stable, the last the most reactive. The products included amino acid dimers as well as cyclic diketopiperazine. The kinetic behaviour of the amino acids differs pressure seems to have a greater effect on the reaction pathway than temperature. As had been recognized earlier, the effect of pressure would have slowed down certain decomposition reactions, such as pyrolysis and decarboxylation (Blank et al., 2001). 

The energy from the decay of radioactive elements was probably not an important energy source for the synthesis of organic compounds on the primitive earth since most of the ionization would have taken place in silicate rocks rather than in the reducing atmosphere. The shock wave energy from the impact of meteorites on the earth s atmosphere and sur-... 

Shock-wave phenomena are important in meteorite impacts where high-pressure minerals are often formed. Small diamonds useful for lapping and polishing are made commercially by shocking graphite mixed with iron and copper. The metals cool the diamonds before they can transform back to graphite on pressure release. 

The shock waves produced by meteorite impacts give rise not only to the obvious craters seen on planets and their satellites but also to subtle effects seen only with chemical and petrographic examination of the shocked material. Shock waves in the interplanetary and interstellar medium play an important role in the formation of stars and planets, including the Solar System. They also produce important chemical effects in interstellar clouds of dust and gas—including the production of rather complex organic molecules. 

The complete or partial resetting of apatite fission track clocks in target rocks by shock-wave heating has been used to constrain the timing of meteorite impacts events (e.g., Wagner 1977, Storzer and Wagner 1977, Hartung et al. 1986, Omar et al. 1987 and Kohn et al. 1995). 

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