Meteors and Meteorites

Both meteorites and meteors are classified more broadly as meteoroids, the simplest definition of which is a small body in space. The term meteor is applied to any streak of light in the upper atmosphere that is produced by a small body when it enters from space. They are more commonly referred to as shooting stars. Efforts have been made to predict and record the occurrence of the most impressive phenomena, and there is wide interest in observing them among both scientists and laypeople.

Meteorites are natural bodies that have managed to travel through the atmosphere to land on the surface of the earth. To accomplish this, they must normally be large and dense enough so that they don't crumble into fragments or vaporize completely. They are of great scientific interest because they provide an opportunity to examine extraterrestrial material older than any material found on earth. Whereas many of earth's early rocks have been destroyed by natural geologic processes, meteorites have remained unchanged since the birth of the solar system. It is now generally accepted that research to determine the age of the materials in meteorites will very likely help us to determine the age of our planet.

Knowledge about and attitudes toward meteorites have undergone significant change through the centuries. There is evidence that many ancient people did accept meteorites as heavenly bodies. Both meteors and meteorites inspired a variety of myths and folk beliefs, with the element of superstition emerging prominently during the medieval [Page 865]period. During the 17th and most of the 18th centuries, the possibility that meteorites had originated from beyond the earth was not even considered.

The last decade of the 18th century marked a distinct forward movement in the scientific study of meteorites. Luckily, witnesses were present when several thousand meteorites fell near L'Aigle in northern France. In 1794, Ernst Chladni, a German physicist, published a book asserting that bodies of rock and metal actually do fall from the sky. He is now considered the founder of the study of meteoristics.

from that time on, museums and interested individuals began collecting samples, making further research possible. At present there are around 1,000 samples available for scientific study. The earliest known meteorite still available for study fell near the village of Ensisheim in the province of Alsace in 1492.

Some specific scientific observations still lagged behind. It wasn't until the 1930s and 1940s that scientists concluded that some craters had originally been formed by the impact of meteorites.

Chrondites represent the most primitive kind of meteorite, making up about 80% of the total. They appear to have been formed with the same substances as the earth and other planets. Their composition is also very similar to that of the sun, with the exception that the sun also contains large amounts of hydrogen, helium, and other noble gases.

In the 1950s, Clair Patterson, of the California Institute of Technology, began the process of dating chrondites by a radiometric process that made use of a uranium-lead clock. He found their age to be 4.55 billion years, and the range of 4.5 to 4.7 billion years has been corroborated by five different radiometric dating methods. The basis for all of these methods has been the measurement of the radioactive decay that has occurred. About 70 meteorites have now been accurately dated. Radiometric dating has also been used to determine ages of many other subjects, including the earth, the moon, fossils, early humans, and a variety of geological events.

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