IMCA Insights – February 2008
A Brief History of Meteoritics
by Norbert Classen

Today, we can hardly believe that meteorites did not attract much serious scientific attention during the early centuries of the Enlightenment. When they did, they were usually explained by atmospheric processes, similar to showers of hail condensing in clouds, or as terrestrial rocks that had been struck by lightning - hence the name "thunderstones". Others believed that meteorites were volcanic rocks, violently spewed out during major eruptions. Noone even considered the possibility that meteorites might be genuine rocks from space.

The Pallas Iron and Ernst Florens Chladni

Until the early 19th century, most scientists shared Isaac Newton's view that no small objects could exist in the interplanetary space - an assumption leaving no room for stones falling from the sky. However, a major shift in paradigms was on its way in the last decades of the 18th century, and it started off with a rather unusual find.

In late 1772, during one of his travels through the remote areas of Siberia on behalf of czarina Catharina the Great, the German naturalist Peter Pallas examined a huge iron mass near the town of Krasnojarsk - a mass of which the Tartars said that it had fallen from the sky. The 700kg iron caught the scientist's attention - it was partly covered with a black crust, and there were lots of translucent olivine crystals (peridots) set in its iron matrix, something Pallas had never seen, nor heard about before. Unwittingly, he had discovered a brand-new type of meteorite, a class of stony-iron meteorites that would later be named for him: the pallasites.

Pallas' subsequent report encouraged a German physicist, Ernst Florens Chladni, to publish his audacious thesis that this and other finds actually represent genuine rocks from space. In his booklet, "On the Origin of the Pallas Iron and Other Similar to it, and on Some Associated Natural Phenomena", published in 1794, he gathered all available data on meteorite finds and falls, forcing him to the conclusion that meteorites actually are responsible for the phenomena known as fireballs, and - yet more important - that they must have their origin in outer space.

Chladni's view received immediate resitance and mockery by the scientific community. In the late 1790s, rocks from space just didn't fit into the concept of nature. However, it was nature itself that came to Chladni's aid in the form of two witnessed meteorite falls, the fall of Wold Cottage, and the meteorite shower of L'Aigle, making him the father of a brand-new discipline - the science of meteoritics.

Wold Cottage, and L'Aigle

On December 13, 1795, a stone of about 25kg was seen to fall in Wold Cottage, England, by several eye-witnesses. The fall occured in broad daylight, out of a clear blue sky, refuting the most popular explanations for the formation of meteorites, such as lightning or condensation in clouds.
The now famous meteorite of Wold Cottage was analyzed by a young and open-minded British chemist, Sir Edward Charles Howard, who found the stone of Wold Cottage, and three other meteorites to contain grains of nickel-iron metal, similar in composition to the iron meteorites described in Ernst F. Chladni's book. In 1802, Howard published the results of his analysis, and his conclusions, convincing a growing number of contemporary scientists that meteorites did actually represent extraterrestrial matter falling from the sky.

However, a large number of conservative scientists kept on denying the obvious facts, among them some of the most influential members of the respected French Academy of Sciences, Paris, France. However, their mockery and sarcasm was silenced some months after Edward Howard's publication: on April 26, 1803, a shower of about 3,000 stones fell in broad daylight near L'Aigle, Normandy, France, witnessed by countless people.
This incident attracted much public attention, providing a fertile ground for further research, and the young science of meteoritics. The French Minister of the Interior commissioned the young physicist Jean-Baptiste Biot, a renowned member of the French Academy of Sciences, to investigate the fall, resulting in a well-written paper that finally broke the spell. The L'Aigle fall and Biot's subsequent publication caused a scientific landslide, a change in paradigms that had been prepared in time by Chladni and Howard, establishing beyond any doubt the fact that meteorites are genuine rocks from space.

The pioneering publications of Chladni, Howard, and Biot kindled a lively interest in the study and collection of meteorites. Major museums and institutions throughout the world started their own meteorite collections, some of which have become famous for their meteorites, such as the Natural History Museum, London, England, the Natural History Museum, Vienna, Austria, the National History Museum, Paris, France; the Museum für Naturkunde, Berlin, Germany, and the American Museum of Natural History, New York, USA, just to name a few.

Museums, Microscopes, and the Evolution of Meteoritics

Besides the macroscopic studies of a growing number of meteorites in institutional collections in the middle of the 19th century, the invention of the petrographic microscope helped a new generation of scientists to recognize the common features of certain meteorites and led to a complex classification system that is still valid today.

The German naturalist, chemist, philosopher, and early private meteorite collector Karl Ludwig von Reichenbach is said having been the first to study the minerals and textures of meteorites with a microscope in 1857. In the 1860s, Henry Clifton Sorby created the first thin sections of rocks and minerals for microscopic study, while Nevil Story-Maskelyne designed a polarizing microscope in 1861 - a microscope which would be the first to study meteorite thin sections in polarized light. Besides that, Story-Maskelyne invented the reflected light microscopy and polished sections. He also was the meteorite curator at the British Museum - all prerequesites of the evolution of meteoritics, and a first classification system that devided the known types of meteorites into three major classes: aerolites (stones), siderites (irons), and mesosiderites (stony-irons).

This classification system was later refined by Gustav Rose at the Mineralogical Museum of the University of Berlin, Germany, who created an elaborate classification system based upon texture and mineral composition of meteorites. He called the spherical bodies typically found in stony meteorites "chondrules", and he dubbed the meteorites containing them "chondrites". He also coined several other designations for meteorite classes that are still in use today, such as "howardites" or "pallasites" which he named in honor of the pioneers of meteoritics, Edward Howard and Peter Pallas.

Rose's classification system was refined, and extended by Gustav Tschermak, the director of the Mineralogical and Petrographical Institute at the University of Vienna, and by Aristides Brezina of the Natural History Museum, Vienna, Austria. Among many other things, Tschermak separated the iron meteorites into three subclasses based upon their texture after acid etching (the hexahedrites, the octahedrites, and the ataxites), while Brezina was the first to introduce the term "achondrite" into meteoritics, meaning meteorites which don't contain any chondrules.

Meteoritics meets the Space Age

The advances in analytical chemistry during the early 20th century marked another milestone in the progress of meteoritics. In 1916, George T. Prior, the Keeper of Minerals of the British Museum, came up with a brand-new classification scheme based upon the principal minerals found in each meteorite, and the ratio of oxidized iron to iron metal for chondrites, the calcium content for achondrites, and the nickel content for iron meteorites.

Prior's classification scheme remained more or less unchanged, and in use until the late 60s of the 20th century. The late 60s didn't just bring about Woodstock and the Sexual Revolution, but also a profound technological revolution, and the Space Age. Brand-new instruments and analytical devices, such as the electron microscope, and the electron microprobe would allow a new generation of meteoriticists to determine the elemental compositions of meteorites, and their minerals with an accuracy never attained before. Trace elements in iron meteorites, for example, could now be determined in great detail, resulting in a new chemical classification system for this class of meteorites.

The progress in nuclear science during the last decades also provided great new devices and tools for the study of meteorites. The isotopic compositions of various meteorites could now be determined, leading to the discovery of oxygen-isotope-ratios as kind of a fingerprint for certain meteorite groups and clans, linking them directly to their respective parent bodies. On the other hand, the advance in optical astronomy provided meteoritics with the possibility to compare selected reflectance spectra of planets and asteroids with the reflectance spectra of certain meteorite groups and clans, thus providing evidence for their specific origins.

Last but not least, the various space missions such as the Apollo program, the Viking Landers, the Pathfinder Mission, and the ongoing robotic research by the rovers Spirit and Opportunity on Mars provided modern meteoritics with the hard proof for the fact that we actually have samples of the Moon and the planet Mars on Earth and available for study - in form of the so-called planetary meteorites. These samples are available for research without having to invest into most expensive space missions first, and in the case of the Red Planet they are currently the only samples availabe for study on Earth. The science of meteoritics which started off as kind of an orphan of natural science has now literally become a spearhead of planetology and planetary science, and there's sure much more to come.

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