Chapter IV: Preface: 5 (3)

Not every annual return of a meteor shower is spectacular, however, since conditions may not be favorable each year for a brilliant display. After all, both parties to a traffic collision at an intersection must try to pass through the intersection at the same time. Our earth, like a well-managed train, always goes through the intersection on schedule, but the particles responsible for meteor showers are much more erratic. They may be early or late—or they may not show up at all. Of the meteor showers seen annually, the Perseids are the most dependable. The Leonids put on their best shows at intervals of 33 years (1799-1800, 1832-33, 1866, etc.). The Giacobinids at intervals of 6½ years (1933, strong; 1939-40, poor; 1946, magnificent).

If you plan to observe a meteor shower, here are some suggestions. You will need:

Acquaintance with the stars, both faint and bright, in the region
containing the radiant of the shower.

Comfortable reclining lawn-chair.

Warm clothing (including blankets) for winter showers or summer ones
at high elevations.

A patient family that will not only approve of your observing but will
help you get up to watch after midnight, when most showers are at
their best.

A corner of your back yard (or sun roof) where you can shade your eyes
from street lights and other illumination.

Timepiece, preferably with radiant dial.

Sit back and watch Nature put on her show. Any records you make may have some scientific value even if you note only these two things: Hourly number of meteors seen. Condition of the sky (clear, hazy, cloudy, etc.) during each hour of your watch.[6] At present, we know of only one instance in which it seems probable that a meteorite came to earth during a meteor shower. The Mazapil, Mexico, iron meteorite fell at 9:00 p.m. on November 27, 1885, during a return of the now very weak Bielid meteor shower. Scientists still cannot decide whether or not a mere coincidence was involved in this case.

As we have already mentioned, most of the cosmic particles rushing into our atmosphere evaporate and do not reach the earth at all except as the tiny congealed droplets and spherules of their own melt. Some cosmic particles, the _micro-meteorites_, are so tiny that they “stall” rather than fall down. These minute objects do not melt or disintegrate and so preserve their original cosmic form unchanged. Scientists have developed various methods for the collection of both of these types of material in order that at least rough estimates of their rate of accumulation on the earth can be made.

One of the simplest methods of collecting this so-called “meteoritic dust” is to expose a sticky glycerine-coated glass microscope slide for at least a 24-hour period in a protected spot well away from locations where any industrial contamination is in the air. At the end of the period of exposure, the “catch” on the slide is examined microscopically, and the individual trapped particles are counted and classified. Meteoritic dust is also carried down to the ground by rain, snow, and hail and can therefore be obtained by filtering rainwater or melted glacier-ice, snow, and hail.

Such collection efforts have been plagued by the difficulty of identifying the particles. How can a collector be sure that the dust he has trapped, even though magnetic and possibly even in part metallic, does not come from some smelter or other industrial plant? Because of such uncertainties, the current estimates of the annual deposit of meteoritic dust for the world range from approximately 20 tons to several million tons. We need improved collection and identification techniques if we are to obtain trustworthy figures.

Recent analyses of rainfall records indicate that the infall of meteoritic dust produces at least one interesting weather-effect. These analyses show that rainfall peaks often occur some 30 days after the appearance of important meteor showers. Apparently, as meteoritic dust particles from the meteor showers filter down through the cloud systems in the lower layers of the atmosphere, the individual particles serve as centers about which atmospheric moisture condenses to form raindrops. The time lag of approximately a month is considered to be due to the very slow rate of fall of such tiny particles. It looks very much as if Mother Nature had beaten man to the idea of “seeding” the clouds to produce rainfall!

9. THE NATURE OF METEORITES

So far in this book we have dealt with meteorites indirectly, chiefly in connection with their fall, distribution, and recovery. In this chapter, however, we are shifting our attention to the meteorites themselves, and will tell what the main types of meteorites are, what meteorites are made of, what they look like, and how to tell them from ordinary rocks.

First of all, meteorites neither all look alike nor have the same composition. The general term “meteorite” applies to any mass that reaches the earth from space. Such masses are made up of metals and minerals in varying proportions. The term “meteorite” is nearly as general in meaning as the word “rock,” which geologists apply to bodies, large and small, that are formed by earth processes and are composed of various kinds of minerals. Actually, there are almost as many different kinds of meteorites as there are kinds of rocks; so you can see that in meteorites a wide range of composition and appearance is possible.

All recognized meteorites belong to one of three main divisions,[7] _irons_, _stones_, and _stony-irons_.

The irons are composed of an alloy of iron and nickel which may contain small inclusions of nonmetallic minerals.

After a cut section of an iron meteorite has been polished, the flat surface, except for possible inclusions, is mirror-like and resembles stainless steel. It appears to be remarkably uniform and uninteresting, but this appearance is misleading. A characteristic and beautiful structural pattern develops when such a polished nickel-iron surface is treated with, for example, a special mixture of nitric acid, alcohol, and Arabol glue.

This process of treatment is known as “etching.” The different structural patterns brought out by such etching give us the basis for classifying the iron meteorites.

If the etching process reveals certain features from which we can infer a cubic, or 6-faced, crystalline structure, we classify the iron meteorite as a _hexahedrite_.

If etching produces a certain special pattern from which we can infer an 8-faced, or octahedral, crystalline structure, we recognize the second subdivision of iron meteorites: the _octahedrites_. This remarkable pattern was discovered and first described by Alois von Widmanstätten, of Vienna, in 1808.

The third subdivision of iron meteorites consists of the “structureless” _ataxites_. (From the Greek for “without arrangement.”) On an ataxite, etching brings out only a finely granular pattern with a stippled appearance.

The _stones_ are composed chiefly of minerals that are combinations of various elements with silicon and oxygen—for example, olivine (Mg, Fe)₂SiO₄. Meteorites belonging to this division also contain combinations of elements with oxygen—such as magnesium oxide (MgO) and aluminum oxide (Al₂O₃). Usually, the stony groundmass contains scattered specks, grains, and thin veins of the same shiny nickel-iron alloy that makes up the iron meteorites almost in their entirety.

The _stony-irons_, as the name indicates, are an “in-between” division. Some of the stony-irons, called _pallasites_, are sponge-like but rigid networks of nickel-iron alloy in which the smoothly rounded openings in the sponge enclose small gemlike masses of olivine. A cut and polished section of a pallasite showing round and oval gems of yellow-green olivine set in a silvery mesh of nickel-iron is a beautiful museum specimen indeed!

In the _silicate-siderites_, another type of stony-iron, a nickel-iron matrix is studded with angular fragments, shreds, and splinters of silicate minerals of all sizes. In the photograph, we can see that each of the various areas of the nickel-iron matrix (lighter in color) exhibits its own distinct crystallographic orientation, as is clearly indicated by the different Widmanstätten patterns.

Even a hasty comparison of polished sections of silicate-siderites and pallasites will leave no doubt that two quite distinct modes of formation were required to produce stony-irons of such different types.

Meteoritic nickel-iron has the following average chemical composition. To the nearest tenth, this alloy contains: Iron (Fe), 90.9%; nickel (Ni), 8.5%; cobalt (Co), 0.6%. This alloy gave scientists the key to the development of commercial stainless steels. It may also contain small amounts of phosphorous, sulfur, copper, chromium, and carbon.

The average chemical composition of stony meteoritic material is somewhat more complicated. To the nearest tenth, the “stones” contain: oxygen (O), 41.0%; silicon (Si), 21.0%; iron (Fe), 15.5%; magnesium (Mg), 14.3%; aluminum (Al), 1.6%; calcium (Ca), 1.8%; sulfur (S), 1.8%. The stony material may also contain smaller percentages of nickel, cobalt, copper, carbon, chromium, and titanium.

In the stony-iron meteorites, we analyze the nickel-iron and stony portions separately. On the average, each of these portions has about the chemical composition that is given for it above.

Mineralogists have identified a variety of familiar minerals in meteorites. These include olivine, the plagioclase feldspars, magnetite, quartz, chromite, and, rarely, microscopic diamonds. All of these minerals are found here on earth in such igneous rocks as basalts and peridotites.

On the other hand, the meteoritic nickel-iron alloys (kamacite, taenite, and plessite, for example) and such meteoritic minerals as schreibersite (nickel-iron phosphide) and daubreelite (iron chromium sulfide) do _not_ occur naturally on the earth.

We should stress here that although unusual _combinations_ of known elements are present in meteorites, no new _elements_ have been discovered during the increasingly intensive study of these masses during the last 150 years.

The majority of stony meteorites show a structure not found in terrestrial rocks. These meteorites are made up of rounded, shot-like bodies called _chondrules_ (from the Greek word for “grain”). The individual chondrules may vary in size from those as large or even larger than a walnut down to dust-sized grains. The most common size is about that of peppercorns. The chondrules are often composed of the same material as the groundmass in which they are imbedded and unless the meteorite containing them is a very fragile one, they will break with the rest of the mass, as will sand grains in a quartzite. If the meteorite is fragile, however, the individual chondrules can generally be broken out whole. Meteorites containing chondrules are called _chondrites_.

A small percentage of stony meteorites have no chondrules. These meteorites are known as _achondrites_ (meaning “not chondrites”) and they resemble terrestrial rocks more closely than the chondrites do. Some achondrites contain almost no trace whatever of metal, although in others (for example, the Norton County meteorite, of Chapter 2) small lumps and specks of nickel-iron are sparsely distributed through the stony groundmass.

Meteorites are as variable in shape as they are in composition and structure. Many are cone-shaped; others shield-, bell-, or ring-shaped; still others pear-shaped. One iron fragment recently recovered from the Glorieta, New Mexico, fall has been described as “macro-spicular,” meaning needle-shaped on a very large scale. The photographs opposite illustrate a number of the commoner forms known. The Glorieta specimen has been nicknamed “Alley Oop’s shillelagh,” for only a person of great strength could wield this 13-pounder with ease!

In general, the shape of meteorites depends upon the amount of mass lost by “evaporation” during passage through the earth’s atmosphere. This factor, in turn, depends not only upon the speed of transit, but also on such physical characteristics of the meteorite as its tensile strength and whether or not it contains certain alloys and minerals that vaporize more easily than the rest of the meteorite. The ring-shape of the Tucson, Arizona, iron is believed to have resulted from the “melting away” of a huge inclusion of stony material during the descent of the meteorite.

When meteorites are recovered and taken to the laboratory for study, one of the first things scientists do is to weigh them. If a meteorite is very large, special scales sometimes have to be constructed for this purpose. Such was the case for the largest meteorite so far weighed: the giant Ahnighito, Greenland, meteorite, which Peary brought to New York City by ship. (See Chapter 3.) A specially constructed scale on which this huge mass is now mounted gives for its weight about 68,000 pounds. Other meteorites famous for their great size are: the Bacubirito, Mexico, 27 tons; Willamette, Oregon, 14 tons; Morito, Mexico, 11 tons; and the Bendego, Brazil, 5 tons. All of these are irons.

The largest stone meteorite so far recovered as one mass is the so-called Furnas County, Nebraska, stone, which is the principal fragment of the Norton, Kansas, fall, and weighs about 2,360 pounds.

At the other end of the size-range, investigators have recovered meteoritic masses weighing no more than a small fraction of a gram. From a stone shower that occurred at Holbrook, Arizona, field searchers have found some of the very smallest specimens in anthills. The insects had carried these tiny meteorites along with sand and garnet grains in building their hills!

The only sure way to determine whether or not an object _is_ a meteorite is to have a small piece of it (say, a fragment the size of an egg) tested chemically and microscopically by an expert on meteorites. Nevertheless, there are several questions whose answers will help you to decide whether or not you are on the right track in suspecting that a “rock” you have found may be a meteorite:

Is your specimen especially heavy?

Does your specimen show a thin blackish or brownish crust on its outer
surface?

Does your “rock” have shallow, oval pits on its outer surface?

If the specimen has a corner knocked off, do you see specks and grains
of metal on the broken surface?

Is your specimen especially heavy? The iron and stony-iron meteorites are very heavy. A 1-inch cube of iron meteorite weighs approximately 8 times as much as a 1-inch cube of ice. Even the stones, which are only about half as dense as the irons, are much heavier than ordinary rocks.

Does your specimen show a thin blackish or brownish crust on its outer surfaces? You will recall that specimens of both the Ussuri and Norton meteorites showed a “glaze” of fused material which we call fusion crust. Most freshly-fallen meteorites are covered with such a crust. To illustrate how this crust forms, consider a snowball that you bravely hold in your freezing hand until the outer surface melts. If you then were to leave the snowball outside overnight, the melted outer surface would freeze into a hard crust.

In similar fashion, the surface of a meteorite melts during the blazing-hot part of its flight through the air, only to “freeze” into a hard, firm coating in the lower, cooler portions of its path. This hardened coating, the fusion crust, is of much importance. Its presence is one of the best indications that a “rock” is really a meteorite. From the character of the fusion crust, experts can piece together a good deal about what happened to a meteorite on its way down to earth. If you should be lucky enough to find a meteorite, don’t break off the fusion crust. A whole encrusted specimen in the hand is worth 200 crustless fragments scattered at your feet!

Does your “rock” have shallow, oval pits or depressions on its outer surface? Such features are known technically as _piezoglyphs_ (Greek _piezein_, to press + _glyph_, to carve) and popularly as “thumb-prints.” They were formed during the meteorite’s flight through the atmosphere when the softer portions of its outer shell were “eroded” away, leaving small scooped-out places. These pittings are very similar to the prints that would be made by the human hand in a lump of modeling clay or bread dough. In one case, they gave rise to the false idea that the meteorite had fallen in a plastic state and that the imprints had been formed when its finders first pulled the mass out of the ground by hand.

If the specimen you have found already has a corner knocked off, do you see specks and grains of metal on the broken surface? Such scattered bits of nickel-iron (not to be confused with the shiny mica flakes often seen in igneous rocks) characteristically occur in the grayish or brownish groundmass of stony meteorites. If your specimen is unbroken, hold it lightly against a spinning carborundum wheel or use a file to grind a small flat surface upon it, and then examine this surface for specks of metal.

If the answers to these questions are yes, then there is a good possibility that you have found a genuine meteorite.

If meteorites remain buried in the ground for a long period of time, their characteristic surface-features may weather away. Under such conditions, iron meteorites develop heavy-layered coatings of rust (iron oxide) as much as several inches in thickness. If irons stay in the ground long enough, they may rust away almost completely and turn into shale balls, like those found near the ancient Wolf Creek, Australia meteorite crater. (See Chapter 4.) Stone meteorites buried in the ground for any great length of time may disintegrate and become completely unrecognizable as meteorites.

The fact that meteorites of all kinds are attacked by weathering has always argued strongly in favor of their prompt recovery. In the case of witnessed falls, prompt recovery is even more important, for only thus can specimens still retaining measurable amounts of various short-lived radioactivities be made available to physicists eager to investigate them with the most modern radiometric equipment.

10. TEKTITES, IMPACTITES & “FOSSIL” METEORITES

Before southern Australia was occupied by the white man, the native tribesmen of that region treasured certain small rounded pieces of black glass as medicine stones, rainmaking stones, and message stones. The Wadikali tribe referred to these objects as _mindjimindjilpara_, a word meaning “eyes that look at you like a man staring hard.” The early European settlers of the area called the same black glassy masses “blackfellows’ buttons.” Both phrases applied to objects that modern scientists call “australites,” which are now one of the best known types of _tektites_ (Greek: _tēktos_, molten).

These Australian tektites and the tektites from many other countries around the world are a problem to meteoriticists. The question is, are they really meteorites? Many investigators believe that the answer is yes, and they are inclined to add to the three main divisions of true meteorites listed in the preceding chapter, a fourth: the tektites.

These mysterious glassy objects occur in such widely separated localities as Czechoslovakia, the Philippine Islands, Borneo, the Ivory Coast of Africa, Australia, Indo-China, Texas, Malaya, and Java. In these and still other areas, they have been found by the thousands in surface deposits of sand, clay, and gravel.

Tektites have never been seen to fall. In spite of this fact, as we noted above, a number of scientists believe that, like the meteorites, the tektites really did come from outer space but, that they fell to earth before man was here to see them come down—or at least before he had acquired the means and skill to make lasting records of such an occurrence.

Tektites are usually quite small, weighing between 1 and 100 grams, although a few of much larger size have been found. One large specimen from the Philippines weighed about ½ pound. Two giant tektites, one weighing ¾ pound and the other over 1 pound, are in the collection of the British Museum. In composition, tektites are an impure silica-glass containing low percentages of the oxides of such elements as iron, magnesium, calcium, and titanium.

If tektite fragments are held under a lamp and observed by reflected light, their thicker parts generally appear to be jet-black. If, however, these same specimens are held up _between_ the observer and the light, then their thin razor-sharp edges are seen to be bottle-green, yellow-green, brownish, or even colorless.

In shape, many tektites are roundish or oval. Others are shaped like dumbbells, ladles, canoes, and teardrops. So they are known by those descriptive terms. One particularly interesting example is the unusual “flanged button” of Australia. Tektites of this type look like miniature South American gold-pans, the _bateas_, heaped high with pay dirt. Australian gold-field workers regarded these tektites as magical, and used them as good-luck charms. Superstitious American gold-seekers brought them into the United States all the way from Australia!

Some tektites (for example, many of the “bediasites” from Texas) are deeply grooved and channeled, and have a very jagged and irregular appearance. Even the smoother tektite surfaces are characterized by flow lines, flow ridges, and bubble pits.

Many weathered pebbles and fragments of obsidian somewhat resemble the tektites superficially. There is a very simple test by which you can distinguish true tektites from obsidian. If you hold a thin splinter of tektite glass in a blowpipe flame, the glass melts quietly but only with the greatest difficulty. On the contrary, when you test in the same flame the terrestrial glass, obsidian, it froths up much more easily, into a bubbly, whitish mass.

Although the question of where the tektites came from is still not entirely settled, most scientists agree that all tektites did have a _common_ origin. For example, tektites from widely scattered localities on the earth’s surface show not only similar queer shapes and surface markings (technically known as “sculpturing”), but also have very much the same chemical composition and, in particular, the same content of radioactive elements.

Because the tektites chemically resemble certain terrestrial rocks, scientists at first believed that some kind of earth process must have created them. One suggestion was that lightning had fused dust particles suspended in the air to form them; another, that they had come from volcanoes; still another, that the tektites were simply inclusions that had weathered out of terrestrial rocks. A few scientists once took seriously the possibility that tektites were refuse from primitive glass factories!

While such theories have not yet been completely discarded, most scientists now feel that the tektites had their origin somewhere outside the earth. There are several reasons for this belief. First, the shape of such unusually symmetrical forms as are found, for example, among the australites, indicates that these small bodies at one time were members of a swarm of freely-spinning liquid masses. Again, flow features observed on the surfaces of certain tektites (and the fusion crust definitely identified on one specimen) show that these bodies at some time must have traveled through the earth’s atmosphere at high velocity.

If, then, the tektites were not produced by earth processes, where did they come from? According to primitive legends, they were “rocks” or “pebbles” from the moon. Indeed, one of the earliest scientific theories as to their origin (proposed by the Dutch authority Verbeek in 1897) likewise attributes them to debris jetted out from the moon. Another holds that tektites are fragments of the outermost glassy layers of some so-called “meteorite-planet,” or planets.[8] Still another idea is that tektites are what is left of a comet when it passes so close to the blazing-hot sun that the “ices” which make up most of the cometary nucleus (head) are all distilled away.

These theories of the origin of the tektites are based primarily on their observed shapes, surface features, and compositions. The senior author of this book has suggested still another possible theory based on the very unusual nature of the observed distribution of the tektites on the face of the earth.

To explain this theory, we first recall that the planet on which we live is more nearly a true sphere than are such familiar “spherical” objects as baseballs or basketballs. Consequently, any plane through the center of the earth cuts its surface in a curve that to all intents and purposes is what geometers refer to as a _great circle_.

Now the significant fact is that all the tektite deposits known at present are located on or very near to three great circles on the earth’s surface. Mathematics shows that if some earth process had created the tektites at random over the surface of the earth, then the odds would be very strongly against the existence of this peculiar “great-circle distribution.” But such distribution along great circles would be _expected_ if the tektites had resulted from what might be likened to “chain-falls” upon the earth of objects like nearby satellites moving in orbits encircling our globe.

This notion brings up the interesting possibility that at some time in the remote past, the earth may have been the proud possessor of a set of equatorial rings. These rings would have been similar to those at present circling in the plane of Saturn’s equator. (Jupiter, too, may once have had its own set of equatorial rings.) The rings of Saturn are known to be made up of countless very small meteorites. In the same way, the “earth rings” of prehistory could have consisted of swarms of tiny nearby meteoritic satellites—the tektites—moving about the earth in the plane of its then-existing equator.

Eventually, the innermost of these small natural satellites collapsed onto the earth’s surface, falling along the old equator. At least twice thereafter, this process was repeated, the points of impact of the later tektite falls again lining up along whatever great circle of the earth happened to be the equator at the time of fall.

As the geologists and other investigators have shown, major shifts have occurred in the position of the earth’s equator during past geologic ages. This fact is well-substantiated by discoveries of fossil shells and plants on the cold Antarctic continent and of glacial deposits in hot South Africa. Therefore, we could hardly expect the tektite deposits, which are believed to have fallen at widely separated intervals of time, to have all occurred along a _single_ great circle on the earth’s surface.

As you can see, the so-called “tektite-puzzle” is a complex one. As if this were not bad enough, Mother Nature has added to the confusion by creating in addition to the tektites another type of silica-glass not only found along the very same three great circles sprinkled with true tektites, but also having other features in common with the tektite glasses.

At Mount Darwin in Tasmania and at Wabar in the Rub’ al Khali desert of Arabia, large and small fragments of this curious silica-glass have been collected. At Wabar the masses of silica-glass were found in and about the rims of a series of meteorite craters formed in nearly pure sand, as we pointed out in Chapter 4. These meteorite craters are known to have resulted from the high-speed impact of iron meteorites upon the sand dunes of the Wabar site. Since the silica-glasses of Wabar have been found to contain countless spherules of nickel-iron of the same composition as the iron meteorites discovered about the Wabar meteorite craters, it seems quite certain that both the sand of the earth target and the nickel-iron of the falling meteorites were vaporized by the intense heat generated at impact. Consequently, it is natural that these Wabar masses of congealed silica-glass and nickel-iron be called _impactites_. They are silica-glasses, created chiefly from _terrestrial_ materials by the impact of large crater-forming meteorites. This same name is now applied to all silica-glasses believed to have the same origin as those at Wabar.

As regards size if not composition, the crater-forming meteorites responsible for the Wabar and other impactites may have been big brothers of the small-fry responsible for the showers of true tektites. Or these big ones may have moved about the earth in orbits distinct from those followed by the tektite swarms but lying in the same plane as one of these swarms.

In addition to the curious puzzle of the tektites, meteoriticists have also run up against the problem of “fossil” meteorites or, more exactly, the problem of the _lack_ of “fossil” meteorites. As we have already mentioned, no positively identified meteorite has ever been found in other than the most recent rock layers. With all the mining—particularly coal mining—that has gone on throughout the world in historic times, this fact does seem astonishing.

A number of explanations can be suggested for this absence of ancient meteorites. In the geologic past, meteorite falls may not have occurred as often as they do today. For example, the primeval atmosphere of the earth may have been so much denser than at present that even quite large meteorites were totally vaporized as they passed through it and therefore never reached the ground. Again, even if the rate of infall of meteorites was the same in the remote past as now, still various weathering processes active ever since the earliest meteorites fell may have so changed them in appearance and composition that they are no longer recognizable for what they are.

Several unusual lumps of rock from England and a mass of iron from Austria, all found at some depth by coal miners, have been tentatively put forward as “fossil” meteorites. But studies of these masses have so far produced no conclusive results. Still, we should not ignore the possibility that someday meteorites may be found and identified in rocks of considerable age.

Does it seem as if we have posed more problems than we have solved in this chapter? It is very true that we have done just that. In speaking briefly about the tektites, the impactites, and the absence of “fossil” meteorites, we have by no means tried to present the last word on the troublesome but highly interesting problems connected with these objects—problems that admittedly may take scientists years or even decades of further research to solve. Perhaps you will find here the kind of unusual and thought-provoking problems that make the study of meteorites a rather special challenge. If so, you may wish to take an active part someday in unraveling these puzzles.

11. OMENS AND FANTASIES

Men seem to have always taken an interest in meteorites, but not until the early nineteenth century were these objects considered to be worth preserving for _scientific_ study.

In the beginning, people believed that because meteorites fell from the heavens, they were either gods themselves or messengers from the gods. The more civilized of early men therefore carefully kept the fallen meteorites. They draped them in costly linens and anointed them with oil. In many instances, the people built special temples in which meteorites were actually worshipped. Some of the holy stones of the ancients, such as the Diana of the Ephesians, mentioned in the Bible as “the image which fell down from Jupiter,”[9] are now thought to have been meteorites.

Meteorite worship was common long ago in the Mediterranean area and in Africa, India, Japan, and Mexico. This practice still persists in some regions even in modern times. The Black Stone of the Kaaba, for example, has been sacred to all Mohammedans from about 700 A.D. right up to the present. It is said to be a meteorite although this fact has never been verified, because strict religious taboos connected with the stone prevent any scientific examination or study of it. On the contrary, the Andhâra, India, meteorite is known to be a genuine one. The story of the fall and preservation of this meteorite provides a fairly modern example of practices rooted in the ritual and custom of far more ancient times.

At about 4:00 in the afternoon of December 2, 1880, the people of Andhâra heard a noise like that made by a gun. Some of the villagers saw a “dark ball” come to earth in a field near them. This falling object sent up a small cloud of dust as it struck the ground. After the stone had been recovered from the field and the dust had been washed from its surface, two Brahmin priests took charge of it and began to collect money for the erection of a temple in which the holy object could be properly displayed.

The scientist who promptly investigated the Andhâra fall reported that throngs of worshippers were crowding into the as yet unfinished brick temple to make offerings of flowers, sweetmeats, milk, rice, water, bel leaves, and of course money. The stone had been named Adbhuta-Nâth, “the miraculous god.” It was shaped like a round loaf of blackish bread and weighed an estimated 6 pounds. The scientist was not allowed to touch it, but he got close enough to verify that the stone was a meteorite covered with a typical blackish fusion crust.

Not only has man worshipped meteorites, but during a period extending from approximately 300 B.C. to 300 A.D., emperors and self-governing cities frequently marked the fall of meteorites by minting special coins or medals known as _betyls_.[10] One of these is the betyl of Emisa, Syria, made by Antonius Pius (138-161 A.D.). The historian, Herodotus, accurately described the object honored by this betyl as: “A large stone, which on the lower side is round, and above runs gradually to a point. It has nearly the form of a cone, and is of a black color. _People say of it in earnest that it fell from Heaven._” The stone is shown on the coin as carried on a quadriga (a carriage drawn by four horses) under a canopy of four sunshades.

Many ancient peoples held meteorites in great reverence, particularly if they were seen to fall. But at the same time, other more practical-minded individuals made good use of the durable and easily worked alloy provided by nature in the nickel-iron meteorites. This alloy was frequently used to make ax-heads, spear and harpoon points, knives, farming tools, stirrups and spurs, and even pots and other utensils. Archeologists have found earrings and similar ornaments overlaid with thin sheets of hammered meteoritic iron in Indian mounds of the Ohio Valley. They have also discovered round beads made of nickel-iron in Indian mounds of the Havana, Illinois, area and in the still more ancient Egyptian ruins at Gerzah.

Meteoritic iron has often been used in the manufacture of special swords, daggers, and knives for members of the royalty. Atilla and other early conquerors of Europe boasted of “swords from heaven.” Emperor Jehangir (1605-1627) ordered two sword blades, a knife, and a dagger to be smelted from the Jalandhar, India, meteorite, which fell on April 10, 1621. In the early nineteenth century, a sword was manufactured from a portion of the Cape of Good Hope meteorite for presentation to Alexander, the Emperor of Russia. Even as late as the end of the nineteenth century, several swords were made from a part of the Shirihagi, Japan, iron meteorite at the command of a member of the Japanese court.

In the Europe of the Middle Ages, meteorite falls and meteor showers, as well as other “unnatural” events like comets, eclipses, and displays of the aurora borealis, were regarded with superstitious awe by commoner and king alike. The medieval mind always sought to interpret events connected in any way with the heavens as somehow influencing the affairs of men. A bishop explained that the great meteor shower of April 4, 1095, forecast “the changes and wanderings of nations from kingdom to kingdom.” The fact, however, that the First Crusade began within a year, is mere coincidence.

In referring to celestial events, Shakespeare often expressed the view that was common in the Middle Ages and the Renaissance. An example is:

The bay-trees in our country are all wither’d
And meteors fright the fixed stars of heaven;
The pale-faced moon looks bloody on the earth
And lean-look’d prophets whisper fearful change,
. . . . . .
These signs forerun the death or fall of kings.
(_Richard II_, II, iv, 8-11, 15)

Yet the descent of meteorites from the heavens was not always regarded as a forewarning of bad fortune. On November 16, 1492, a 279-pound meteorite fell at Ensisheim in Alsace, not far from the battle line separating the armies of France and the Holy Roman Empire. Emperor Maximilian, the leader of the Empire’s forces, commanded that the fallen stone be carried to his castle. There a formal war-council was held to determine what the strange event could mean.

The Emperor and his councillors decided that the fall of the meteorite at such a time and place was an omen of divine favor which meant good fortune to the cause of the Holy Roman Empire. After breaking off two small pieces of the stone, one for the Duke of Austria and one for himself, the Emperor forbade further damage to it. He also gave orders that the stone be hung in the parish church in Ensisheim for all to see. In this way, the Ensisheim stone became the very first meteorite of witnessed fall to be preserved down to the present day—and all because of the superstition of a famous military leader.

The discussion to this point makes clear that in ancient, medieval, and Renaissance times, meteorite falls were considered as startling and disturbing events, which frequently were interpreted in strange and mistaken ways. But the fact that meteorites actually did fall from the heavens was not questioned. As the so-called “Age of Reason” opened, a curious change in attitude toward meteorite falls took place.

At the very time that knowledge in general increased, men of learning began to deny that meteorite falls occurred at all! The scientists of the French Academy, in particular, were very positive on this point. Since the era was one in which all Europe sneezed if “la belle France” had a cold in the head, it was a trying time not only for the early meteoriticists, but for all who had the nerve to insist they had seen rocks fall from the sky.

By the end of the 1700’s, the authorities had studied the evidence relating to meteorite falls and had completely rejected it. They said that there was no “proof” whatever that “stones fell from the heavens.” These early scientists openly sneered at people who claimed that they had seen meteorites fall. It was felt that the spectators of such events either had merely been “seeing things,” or had surely been reporting light and sound effects connected with nothing but ordinary thunderstorms.

When confronted with the “fallen” masses themselves, the authorities often refused to examine them, or if they did, insisted that these masses were only rocks that had been struck by lightning. Such were the opinions of learned men around the close of the eighteenth century.

Fortunately, scientific facts have a stubborn way of winning out in the long run. A major part of the credit for seeing that the truth regarding meteorite falls was at last recognized must go to E. F. F. Chladni, a German physicist, and to Edward Howard, an English chemist.

In 1794, Chladni published an extremely important paper concerning a large spongelike mass of “native iron” found near Krasnoyarsk, Russia. This object had been discovered in 1749 by a Russian blacksmith, and it was studied in 1772 by P. S. Pallas, an early traveler. Chladni concluded that the mass of iron[11] must have fallen from the heavens, because it had been “fused” (but not by man, electricity, or fire) and also because there were no volcanoes anywhere around its place of find.

Chladni supported his theory by listing numerous reports of meteorite falls dating from ancient and medieval times. But Chladni’s fellow scientists flatly rejected his theory as clever but not satisfactory.

With the fall of the Siena meteorites in Italy on June 16, 1794, the controversy regarding the possibility that stones actually fell from the sky became particularly heated, and remained so for nearly ten years. During this interval, two other important meteorite falls occurred: Wold Cottage, England, on December 13, 1795, and Benares, India, on December 19, 1798. Scientists had a hard time finding explanations for these well-observed events, and some of the theories put forward to account for them far outdid Chladni’s in “cleverness,” if that be the correct word.

One scholar, writing in 1796, suggested that the masses which fell at Siena resulted from the solidification at great height of volcanic ashes from Mount Vesuvius. These ashes had supposedly been carried northward beyond Siena and then been “brought back by a northerly wind, congealing from the air....”

Fortunately, in 1803 Edward Howard’s chemical work on meteorites came to a successful conclusion. This patient chemist made analyses of samples from the Siena, Wold Cottage, and Benares falls and from an older Bohemian fall. He also had the samples studied mineralogically by a fellow scientist. From the results of these investigations, he drew the following conclusions, which admirably supported Chladni’s well-reasoned and thoroughly documented theory regarding meteorite falls:

All four of the stones studied had very nearly the same composition.

Despite the fact that the stones contained no new elements, their
mineralogical character differed in several important respects from
that of any rocks found naturally on the earth.

The four masses must have had a common origin although their reported
falls had been widely separated both in time and in space.

Finally, said Howard, it was quite possible that the stones had really
fallen from the sky.

Howard’s views were soon put to the test. Shortly after the publication of his important paper, a shower of stony meteorites fell near L’Aigle, France, on April 26, 1803. This event was carefully investigated by French scientists, and they reluctantly admitted that about 3,000 stones actually had fallen within an oval-shaped area about 6 miles long by 2 miles wide. This shower of meteorites had been accompanied by the same light and sound effects mentioned in many of the old meteorite-fall reports collected by Chladni, effects now recognized as characteristic of the infall of meteorites upon the earth. The evidence was overwhelming—stones really did fall from the sky. In the camp of the enemy, so to speak, the reality of meteorite falls was established once and for all!

12. THE MODERN VIEW

After the L’Aigle shower of 1803, a whole new era opened in the study of meteorites. No longer did scientists hold these objects up to ridicule and scorn. Instead, they came to regard meteorites as well worth collection and careful study.

The Vienna Museum, the British Museum, the Paris Museum, the Academy of Science of St. Petersburg (now Leningrad), and the U.S. National Museum began to build up splendid meteorite collections. Scientists in Germany, England, France, and Russia engaged in the painstaking mineralogical study and classification of individual meteorite specimens.

The modern science of meteoritics is rooted deep in the nineteenth century. Many special fields of investigation had their beginnings then. Scientists became interested in the chemistry, the mineralogy, and the metallurgy of meteorites; in the orbits of meteorites and the trajectories they follow through the earth’s atmosphere down to impact with the ground; and in the distribution of meteorite falls in space and time.

From this period we can date such milestones of progress in meteoritics as:

The discovery of the beautiful and significant Widmanstätten patterns
characteristic of the majority of the irons, and the less spectacular
but equally important lines named for J. G. Neumann, the German
meteoriticist who discovered them, in 1848, in the Braunau meteorite.

The realization that there were many different kinds of meteorites and
that these diverse objects were very important to an understanding of
the internal structure and origin of the earth, and perhaps of the
Solar System and the wider cosmos as well.

Tentative explanations of the violent and terrifying light and sound
effects connected with meteorite falls.

Tentative explanations of such oval-shaped areas as shown above.

By 1850, A. Boisse, an early French geologist and meteoriticist, had put forth the basic _meteorite-planet_ hypothesis. According to this theory of his, meteorites are the fragments of a planet[12] that formerly orbited between Mars and Jupiter in what is now called the “asteroid belt.” And untold millions of years ago, this planet was shattered by some unknown but very great force, possibly collision with another celestial body.

The structure of the meteorite-planet was considered to have been very much like that of the earth. The various divisions of recognized meteorites were believed to be representatives of the several concentric, or nested, shells of material originally making up the destroyed planet. These shells were progressively less dense with increasing distance from the center of the planet.

Today Boisse’s theory is one of the most widely accepted as an explanation of at least one major category of the meteorites. Some modern investigators would insist that the meteorite-planet had a thin outer glassy shell from which the tektites came.

Most of the larger fragments of the meteorite-planet, now called the _asteroids_, move so that the average asteroidal orbit very closely approximates the orbit of the original planet. But many of the smaller fragments follow paths in space that differ considerably from the original meteorite-planet’s orbit. Even some of the asteroids behave this way, either because of the high speeds they acquired at the time of disruption of the meteorite-planet, or because of the later influence of the major planets and particularly of the giant planet, Jupiter.

In fact, at the present time, several asteroids move well within the orbits of the earth and Venus. It is quite possible therefore that such a large meteorite crater as the one at Canyon Diablo, was produced by the prehistoric fall of one of these small members of our Solar System. If so, we have reason to believe that a core-fragment of the meteorite-planet came to earth at Canyon Diablo. For the extensive mining operations carried out there during the last half-century have shown that the projectile responsible for this greatest of all meteoritic shell-holes in the face of Mother Earth was a mass of solid nickel-iron, which in all likelihood was core material.

The lengthy and costly series of mining operations at Canyon Diablo were all undertaken in the hope of locating the “main mass” of this huge projectile and thus of opening up what might be called a cosmic-lode of quite valuable metals. Unfortunately, the miners overlooked the fact that impacts at meteoritic speeds produced almost incredible amounts of heat. Even the solid iron meteorites are vaporized and widely dispersed at the temperatures resulting from such impacts, as we have seen was the case at Wabar (see Chapter 4). So it was at Canyon Diablo.

The idea of a cosmic-metal mine might at first strike some readers as too futuristic to take seriously. But the necessity for catching a core-fragment before it enters the consuming atmosphere of our planet is really nothing new. As far back as 1939, the senior author had occasion to point out that if we wish to start a successful cosmic-metal mine, we must catch our core-fragment before it is turned into unminable vapor. This point will come up again in the next chapter.

The _iron_ meteorites came from A, the dense nickel-iron core.

The stony-iron meteorites came from B, the intermediate zone of
cellular nickel-iron and silicate minerals.

The _stony_ meteorites came from C, the outer zone of silicate
minerals in which relatively little or no nickel-iron is present.
The chondrites were believed to come from the inner portion of this
zone; the achondrites, from the outer portion.]

There are several other theories of the origin of meteorites interesting enough to mention. The early view that the meteorites were debris thrown out by ancient volcanoes on the moon or recent ones on the earth came to be discredited largely on physical grounds. On the other hand, extremely violent _primordial_ volcanoes on the earth (not the weak ones of historic times, like Aetna or Vesuvius) could have ejected material that in much later times fell, and continues to fall back on our globe. This theory has not been ruled out and it still receives support, for example, from some authorities in the U.S.S.R. These same Russian scientists take most seriously a suggestion that the meteorites (and comets as well) were thrown out by volcanoes believed to exist on the planet, Jupiter—a theory dating back almost a century to the English astronomer, R. A. Proctor.

Some scientists believe that meteorites represent the congealed remains of gaseous bolts of matter ejected by the sun. Others interpret them as fragments of comets that have been torn apart by passing too close to the sun, which is the most powerful gravitational center in the Solar System.

Chemists, geologists, astronomers, and physicists—as well as the meteoriticists themselves—are constantly working toward a solution of the problem of the meteorites. Where do these bodies come from? What can we learn from them about their age and origin and about the age and origin of our Solar System? Years may be required, but eventually the riddle of the meteorites will be solved by the patient, concerted efforts of men and women of science.

13. PRESENT AND FUTURE APPLICATIONS

So far we have considered what might be called the “pure” rather than the “applied” side of the study of meteorites. The investigator in any pure science asks of a new discovery, “What does this tell me about the universe? How does it better help me to understand the laws of nature?” Of the same discovery, however, the worker in an applied science will ask, “What practical use can be made of this gain in knowledge? What can it be made to do for mankind in general?”

These questions reveal a decided difference in viewpoint, but this difference does not reflect unfavorably on either class of scientists. In fact, there is a great deal of truth in the saying “Today’s pure science is tomorrow’s applied.” Actually, ways and means of taking advantage of seemingly useless scientific discoveries are constantly being found. The most famous example of this principle is the development of the atomic bomb from the results of Einstein’s researches in the abstract field of relativity. Here the seemingly mystic formula E = mc² came to have far-reaching practical applications indeed!

Meteoritics has some exceedingly practical applications. Far from being completely “out of this world”—as the recovered meteorites themselves originally were—this science has been and can be made to serve mankind in a number of rather unexpected ways. Meteoritics, the onetime “stepchild of astronomy,” is currently being regarded with ever-increasing respect by scientists and engineers working in many different fields.

Consider, first of all, the stainless steels that are so widely used in modern industry, and even the fine satin-sheen stainless “silverware” that graces our dining tables. These have wisely been patterned after a natural alloy with lasting qualities of strength, tenacity, and resistance to corrosion. This natural alloy is the one making up the iron meteorites.

Its toughness and durability became well known wherever attempts were made to section these metallic meteorites. Specially designed and extra-powerful sawing equipment is required to slice meteoritic iron, and even with it, progress is painfully slow. So astounded were those who first tried to cut iron meteorites with ordinary metal saws that one of the earliest practical results was the development of battleship armor plate composed of a commercial alloy called “meteor steel,” which mimicked the composition of the iron meteorites.

Of course, a good deal of the difficulty of sectioning meteorites arises from the fact that those doing the cutting are trying hard not to waste valuable meteoritic material. Every precaution is taken to keep the amount of “sawdust” to a minimum, for such finely ground up and contaminated meteoritic material is of little scientific use. And, in addition, scientists must guard against heating meteorites to high temperatures because such heating destroys the delicate internal structure of the masses. If these two considerations (loss of material and overheating) were unimportant, even a large meteorite could easily be divided up by use of such high-powered oxyacetylene torches as are used to dissect huge obsolete battleships.

At the Institute of Meteoritics, a thin, water-cooled blade of soft iron is driven slowly back and forth by an electric motor. Carborundum grit in water suspension is fed evenly into the narrow cut over its entire length. This grit becomes imbedded in the lower edge of the soft iron blade, which then acts as a “many-toothed” metal saw. Several meteorites can be sectioned simultaneously by this multiblade saw. In the future, such newly developed methods as high-speed particle jet streams or ultrasonic devices may be used to section meteorites both rapidly and economically.

In the field of cosmic ray studies, particularly those concerned with the protection of space travelers from harmful radiation, meteoritics can be of help. The recovered meteorites have already come through those regions that would be crossed by even the farthest-ranging spaceships. Consequently, a great deal can be learned from the study of meteorites about the intensity of the cosmic radiation that the crews of such ships must face once they get outside the earth’s protective air-shield.

The first study of this type was made in May, 1948, at the Institute for Nuclear Studies of the University of Chicago (now the Enrico Fermi Institute). Scientists made radioactivity tests on samples of the Norton County meteorite donated for this purpose by the Institute of Meteoritics and air-expressed to Chicago because of the intense interest in the radioactivity question. In October, 1949, English investigators ran similar tests at the Londonderry Laboratory for Radiochemistry, Durham, England, on samples of the freshly fallen Beddgelert, North Wales, meteorite discussed on pp. 69-70. The results of these two pioneer studies were negative because the “Model-T” instruments available in 1948 and 1949 were not sensitive enough to detect the relatively low radioactivities present.