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_. [Illustration: Every plane passing through the center of a sphere intersects the surface in a great circle. In this figure, only the front half of the great circle cut out by the plane is shown.] 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.