Word: earthly
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Dates: during 1950-1959
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Most information about the earth's interior, Mathematician Bullen pointed out, has been gained by recording and measuring the several kinds of waves sent out by earthquakes. As the waves travel through the earth, they are bent and reflected in complicated ways. Some waves move faster than others; some are absorbed entirely. By disentangling the jiggly lines made by instruments recording many earthquakes, seismologists have determined that the earth is formed of concentric layers of different materials, with iron-nickel at the center and stony oxides nearer the surface...
...Warning. Natural earthquakes, said Dr. Bullen, are not ideal as tools for earth study. Their waves often start from a large region, which makes them leave fuzzy records, like the shadows cast by a bonfire. Even worse, they give no warning, so seismologists have no time to start up the expensive, sensitive instruments they use when they want to record events of special interest...
Nuclear explosions are not nearly as powerful as major earthquakes, but even old-style A-bombs can send waves strong enough to pass right through the earth. They come from a small area whose position is accurately known, and since the time of the explosion is under human control, warning can be given when the man-made waves are about to start through the earth...
Bullen thinks that much better results could be obtained from smallish A-bombs exploded at places selected by seismologists. If they were placed below the earth's surface or under the sea, much more of their energy would turn into useful earth waves. The exact time would be told in advance, so scientists all over the earth could have their instruments tuned to concert pitch. A radio signal might start abreast of each burst of waves. When the earth's gentle, controlled trembling finally quieted down, the scientists would have data for a new understanding of its mysterious...
...Bullen expressed gratitude. There would not be time, he said, to set up special apparatus in remote places, but the world's 600-odd established seismic stations will be listening. The waves from Nevada will surely be recorded all over the earth...