Rocks have been falling on the earth for billions of years. These rocks from our celestial neighbors pass through the atmosphere with a fiery glow and thunderous rumblings. At this point they are referred to as meteors; when they hit the Earth's surface, they are then called meteorites. Most of the 20 tons or so of extraterrestrial materials that strike the atmosphere each day is in the form of tiny cometary dust grains that burn up as "shooting stars." Occasionally, a walnut to grapefruit size meteorite will fall. Less often a much larger one will fall and may be cause minor damage. Statistically, every 2000 years a 50-meter-diameter meteorite will slam into the Earth and form a crater a little more than a kilometer in diameter. The immediate aftermath has a devastating effect on life in the surrounding 400 square kilometers, similar to the impact 50,000 years ago that formed Meteor Crater, Arizona. Every 50 to 100 million years, a 10-kilometer-diameter "killer" asteroid will strike and cause global extinction like the asteroid that struck Yucatan, Mexico 65 million years ago and wiped out the dinosaurs.
Artist's impression of the Chicxulub impact that caused the extinction of the dinosaurs.
Fortunately through recorded history, only a few people have been struck by meteorites, several houses are known to have been ventilated, a car was demolished in New York, and an unlucky dog was supposedly killed in Egypt by the fall of the Martian meteorite, Nakhla. For most of us, meteorites are fascinating and beautiful objects from other "worlds," namely the Moon, Mars and a variety of large and small asteroids. When you hold a meteorite, you can feel the mysteries of another planetary body that has witnessed an incredible amount of cosmic history over millions of millennia. Aside from our fascination, meteorites give science a recorded history of our solar system from the time before the sun and planetary system, about 4.6 billion years ago (4.6 Gya), to the present. From meteorites, science has established theories about how planets formed and evolved and even how primitive life on earth may have originated.
Incredibly, until the late 18th century, scientific understanding of meteorites was limited by extreme prejudice and ignorance. Bias was manifest in the belief that no stones or iron objects could fly around in space and the idea that they could fall from the sky was "absurd." Mind you, this was 18th century Europe where there were more than a few bright, scientific minds operating. Despite the witnessing of many meteorite falls in Europe during the last half of the 18th century, excuses were drawn whereby stones were either blown into villages by strong winds or they were ejected from distant volcanoes or even from volcanoes on the moon!
Ernst Florens Friedrich Chladni (1756-1827)
Finally in 1794, Ernst Florens Friedrich Chladni in Germany published a book on the observations of meteorite falls and concluded that stones and irons did indeed fall from the sky and were probably material left over from the formation of planets that were eventually delivered to Earth by collisions in space. Brilliant! It helped that during the time that the book was published and shortly afterwards, a mass of stones fell on Siena, Italy in 1794 and a 56-pound mass fell on Wold Cottage, England in 1795. The final blow against ignorance and bias struck in 1803 when about 3000 stones rained down over L'Aigle France. The French Academy of Sciences sent Jean-Baptise Biot to investigate. Biot's paper describing how these stones were undoubtedly of extraterrestrial origin marks the beginning of the science of meteoritics.
Jean-Baptiste Biot (1774-1862)
However, it had not taken such a large number of falling stones to enlighten prehistoric cultures about where meteorites came from. Many burial sites in the Western World have yielded meteorites that obviously had great significance to the respective cultures. For example, the large, 1.5 ton Casas Grandes, Mexico iron meteorite was found in the ruins of a pre-Aztec burial vault, wrapped like a mummy. The Camp Verde, Arizona iron meteorite was found on an 800-year-old Sinagua "altar," wrapped in a feather blanket and was probably transported from Meteor Crater approximately 100 km to the northeast.
During the 19th century, much was learned about meteorites through the use of chemical analyses and the petrographic microscope. Such a microscope looks at the transmission of polarized light as it passes through very thin slices of rock, which can be used to identify constituent minerals. Modern scientists now have a marvelous assortment of sophisticated instruments that, for example, can detect one atom of an element among millions of others and microscopes that can actually see atoms and mineral unit cells, the building blocks of solid matter. We probably know more about meteorites than we do about most terrestrial rocks.