Popular Science Monthly/Volume 64/February 1904/The Geographical Distribution of Meteorites
|THE GEOGRAPHICAL DISTRIBUTION OF METEORITES.|
FIELD COLUMBIAN MUSEUM.
SPEAKING broadly, we know as yet of no fundamental reason why meteorite falls should be any more numerous upon one part of the earth's surface than upon another.
Compared with the vast area of space in which meteorites wander, our earth is but a point, which draws into itself from time to time one of these masses. Moreover, it is a rotating and wabbling point, ever presenting new surfaces to the portions of space in which it is traveling. The marksman who displays his skill by shooting glass balls thrown into the air would have the difficulty of his task enormously increased if he should endeavor to strike successively the same point upon the ball, especially if it had in addition to its forward motion one of rapid rotation about a wabbling axis. It is true that there is some prospect of our being able after much study and comparison of data to locate a few meteorite swarms with sufficient accuracy to warrant a conclusion as to what point upon the earth stones from them will strike, but this possibility seems at present quite remote. At present we can only presume that a gentle rain of meteorites has fallen regularly and impartially upon the earth since the morning stars first sang together.
The latest and best calculations, which are by Professor Berwerth, of Vienna, have shown that the number of meteorites actually falling upon the earth at the present time each year, not including of course shooting stars or meteors, is about nine hundred. Two or three of these bodies fall, then, somewhere upon the earth every twenty-four hours. But about three fourths of the earth's surface is covered with water, and the missiles impinging upon this area are lost. Upon the remaining one fourth, however, 225 falls should take place, accompanied by phenomena such as to make the occurrence noteworthy, A large part of the land is, however, unpopulated and our figure of 225 may, therefore, be cut in half in order to take account of this factor. Again, falls taking place in the night would, in many cases, not be observed, and as a last concession we may halve our figure on this account. It would finally seem then that about 55 meteorite falls capable of record might be expected to take place each year, and in a century the total should be 5,500. As a matter of fact, the total number of recorded meteorite falls, including some from as far back as the fifteenth century, is only about 350.
The first conclusion one is likely to draw from results so contradictory is that the original premise is entirely at fault. Yet within the small area of France 50 well-authenticated meteorite falls have taken place within the last one hundred years. We have no reason to suppose France especially favored of the gods in regard to the number of meteorites which it receives and, as it covers only about one one-thousandth part of the earth's surface, we shall find by reversing the calculations made above that our original figure of 900 a year is fully substantiated. The difficulty will be somewhat explained by a glance at the accompanying map. Tracing upon this the locations of known meteorite falls, we see at once that they are largely confined to the civilized nations, or, with the exception of the Semites of Africa and Arabia, to regions inhabited by the Caucasian race. Of a total of 63i known meteorites, 256 are located in Europe and 177 in the United States. In other words, more than two thirds of the whole number known belong to countries which occupy but about one eighth of the land surface.
We reach then the rather curious conclusion that the ability to observe and record meteorite falls is a mark of civilization, and that the relative civilization of regions equally populated may be judged by the numbers of meteorites known from each. The superiority of civilized peoples in this regard comes probably not so much from their greater ability to observe the fall of a meteorite as from their better facilities for recording such an occurrence and for preserving the stone which has fallen. To an unorganized community, the fall of a meteorite is an isolated occurrence, impressive enough at the time, but so infrequent that in the absence of records or means of communication with other communities, it is lost sight of. Civilized communities with their means of records and museums are able to correlate such occurrences, and in time accumulate important knowledge regarding them. So upon the accompanying map there are depicted not only the places where meteorites have fallen, but the isolation of China, the bleakness of Canada, the impenetrability of South America, the hollowness of Australia and the darkness of Africa. Meteorites known from uncivilized countries should for the most part be credited to travelers from civilized nations.
It would be quite superficial, however, to suppose that the distribution of Caucasian peoples is the only important factor affecting the location of known meteorite falls. There are evidences that other factors, the nature of which can hardly be even suggested as yet, affect the place of fall of meteorites. Thus, there appears upon the accompanying map a tendency of these bodies to flock toward mountainous regions. This is indicated by the large numbers of them occurring in India near the Himalayas, in Europe in the vicinity of the Alps, in the United States about the southern Appalachians, and in the Americas up and down the great western mountain range. It is possible that investigation will show that greater gravitational force is exerted at these points, and that thus the number of meteorites drawn in is there
increased, or, again, mountains may present actual mechanical obstacles which stop and accumulate meteorites. Whether either of these hypotheses has any foundation in fact, however, is not known as yet. There are again remarkable differences in the kinds of meteorites found in the two hemispheres. Thus, taking falls and finds together, of the 256 meteorites known from the western hemisphere, 182 are irons and only 74 stones; while from the eastern hemisphere, of 378 known, 299 are stones and only 79 are irons. Professor Berwerth has sought to account for the excess of irons in the new world by the suggestion that the dry air of the desert areas which abound in this hemisphere has preserved meteorites fallen in long distant periods, while those of a similar age in the other hemisphere have been exposed to a moist climate and have for the most part been decomposed. It is true that many of the iron meteorites known from the western hemisphere occur upon the Mexican and Chilean deserts, but quite as many come from the southern Appalachians, where a comparatively moist climate prevails. There are also numerous desert areas in the old world perhaps as fully explored as those of the new, so that on the whole the above explanation seems inadequate.
Other remarkable groupings of meteorites with regard to their geographical distribution may be noted when areas smaller than hemispheres are compared. Thus of a total of nine meteorites belonging to the peculiar class called howardites, five have fallen in Russia. Of the nine meteorites known belonging to the still more remarkable class of carbonaceous meteorites, three have fallen in France and two in Russia.
Again small areas of equal extent and equally well populated vary curiously in their number of meteorite falls. Within the state of Illinois, for instance, no meteorite is known ever to have fallen, while in the state of Iowa, which has about the same area, but a smaller population, four falls have been noted, and from the state of Kansas, which has a larger area than Illinois, but a smaller and less uniformly distributed population, twelve meteorites are known.
It is usual to dismiss inquiries regarding the meaning of such groupings with the remark that they are mere coincidences. But it is the mission of science to investigate coincidences, and however long the task may be of determining the laws which bring about the particular occurrences here referred to, there can be no doubt that they are the result of law and of law which will some day be discerned by the human mind.