According to this theory, convection processes in the only partially solidified outer shell of the youthful moon could have given rise to great numbers of surface features having the size, shape, and distribution of the common lunar craters. In far more satisfactory fashion than any other theory so far proposed, the convection-current hypothesis of Wasiutynski explains the many and distinctive characteristics of the non-ray craters on the moon.
RECOGNIZED METEORITE CRATERS OF THE WORLD
| NAME | LOCATION | DATE OF RECOGNITION |
|---|---|---|
| Canyon Diablo | Coconino County, Arizona | 1905 |
| Odessa | Ector County, Texas | 1929 |
| Henbury | McDonnell Ranges, Central Australia | 1932 |
| Wabar | Rub’ al Khali, Arabia | 1932 |
| Campo del Cielo | Gran Chaco, Argentina | 1933 |
| [2]Haviland (Brenham) | Kiowa County, Kansas | 1933 |
| Mount Darwin | Tasmania | 1933 |
| [3]Podkamennaya Tunguska | Yeniseisk District, Siberia | 1933 |
| Box Hole Station | Plenty River, Central Australia | 1937 |
| Kaalijarv | Oesel, Estonia | 1937 |
| Dalgaranga | Western Australia | 1938 |
| Ussuri (Sikhote-Alin) | Eastern Siberia | 1947 |
| Wolf Creek | Wyndham, Kimberley, Western Australia | 1948 |
| Aouelloul | Adrar, Western Sahara | 1952 |
5. HEAVEN KNOWS WHERE OR WHEN
Meteorites have been falling upon our planet for a long time—how long, it is hard to say with accuracy. Up to now, no specimens certainly identified as meteorites have been found in ancient rock layers. Scientists have been able, however, to estimate the age of several meteorite craters on the basis of the degree of weathering not only of the crater rims, but also of the meteorites found around the craters. Age estimates have also been based on the ages of fossils found in silted-up crater interiors and on other related indirect evidence.
As we have already noted, the Canyon Diablo, Arizona, crater is thought to be 20,000 to 70,000 years old. The Odessa, Texas, crater is at least 200,000 years old; and the Haviland (Brenham), Kansas, craters more than 600,000 years old. Clearly, meteorite falls have been occurring over a very long period of earth history.
For many years, scientists have studied the distribution of recovered meteorites around the world in an effort to find out whether there are any places on the land surface of our globe where meteorites have fallen in unusually large numbers.
The idea that any particular spot on the land surface of the earth might in some way attract more meteorites to it than other locations seems unreasonable because of the very nature of the target presented by our planet to the meteorites wandering through space. Not only is the earth in motion, but it is in very complicated motion. Our earth revolves about a sun which is also in motion through space. At the same time, the earth is rotating on its axis. A single point on the surface of the earth therefore traces a very erratic path in space with the passage of the years, and the likelihood that this particular point would be struck by more than one meteorite (if indeed by one!) must be very small.
Studies have shown that the people of the earth have a great deal more to do with “concentrations” of meteorite recoveries than anything else. Population density is the first important factor. Clearly, the more people living in a given area, the higher the probability that a meteorite fall will be seen and reported and that the fallen mass itself will be recovered. A prime example is India, one of the most densely populated regions of the world. Of the 102 meteorites recovered in that country up to 1953, 97 were of witnessed fall. This extremely high proportion of falls is undoubtedly due to the fact that for centuries such an event could hardly have taken place in that country without attracting the attention of large numbers of people. Apparently, the majority of Indian meteorites have been recovered as they fell, for only 5 unwitnessed falls are recorded for that country.
On the other hand, from French West Africa only 5 falls and 3 finds have been reported throughout an area slightly larger even than India’s. This country thus provides an example of a sparsely populated region, in many provinces of which a meteorite fall might pass unobserved, and a fallen meteorite might remain undiscovered.