File:The continent we live on (1961) (20496414020).jpg

Title: The continent we live on
Identifier: continentweliveo00sandrich (find matches)
Year: 1961 (1960s)
Authors: Sanderson, Ivan Terence, 1911-1973
Subjects: Physical geography; Natural history
Publisher: New York : Random House
Contributing Library: New College of California
Digitizing Sponsor: Internet Archive

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example, the weight of which has been estimated at four million tons. The diameter of the Arizona crater is about 4000 feet; that of the Chubb is over three times greater. When the Chubb meteorite walloped into the bare rock of the Ungava plateau it must have set up a very considerable seismic disturbance. So also must several of the others that landed in Canada. Now meteorites are thought to be bits of some much greater body, possibly a planet, that broke up or exploded somewhere within our solar system, for they come in three major types—iron, iron- rock, and rock. The actual chemical composition of these is odd. in that among the iron and iron-rock types there are found some minerals that do not exist on this earth. The falls of meteorites have been observed through the ages and recorded since history was first written. Also, considerable numbers of meteorites of all three classes, plus another type known as glass meteorites or tectites. have also been found scattered all over the surface of the earth, in most recent de- posits. Meteorites have also been among the most holy and therefore priceless collections of men since the Stone Age. Further, large numbers of iron meteorites were "used up" by primitive man before he learned to extract that metal from ores, as has been shown by a chemical analysis of many of the earliest iron artifacts so far discovered. Meteoritic iron seems to have been man's first source of that metal. However—and this is the really extraordinary fact—although iron and iron-stone mete- orites seem, on a purely statistical basis, to have been falling all over the earth at a regular though now diminishing rate throughout historic and prehistoric times, not one single one or even tiniest part of one has ever been found in any of the billions of tons of building stone, coal, salt, or any other rocks or deposits that have now been mined by man for thousands of years. The earliest known are from gravel and other compara- tively recent surface deposits laid down not earlier than half a million years ago; so it would seem that, prior to that time, no meteorites fell on this earth. At the same time, working from quite another angle, there are those investigators who have brought forward evidence to show that, whatever large planetary body broke up to give rise to the iron, iron-stone, and possibly stone meteorites, it did so only about 300.000 years ago. Some of these investigators, along with other scientists, have suggested that a planet between Mars and Saturn then blew up, giving rise both to meteorites and to the Asteroid Belt. Some of the resulting "junk" then for a period crossed the path of our planet, which gathered it up slowly by running into it and so clearing a path through it. The Moon, because of its lack of atmosphere, acts like a vast broom as it sweeps around the earth, covering a much wider front than we do. Most of this debris was received by the Moon and because of its lack of atmosphere was not burned up. Also, if its surface is covered with deep ultrafine dust, even a small meteor might make a tremendous impression on its surface. The pursuit of meteoritic craters can be fascinating, and their discovery can yield some really unique insights into the vegeta- tion, and thus into animal life; for they constitute the one truly erratic and unpredictable physical force coming from outside that may upset the even tenor of events on this earth. If they— 33

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