
... Science Frontiers ONLINE No. 67: Jan-Feb 1990 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Continuity At The Conrad Discontinuity From the study of seismic waves, geophysicists have determined that between 7.5 and 8.6 kilometers below the surface there exists a clear-cut "discontinuity." Practically speaking, this means that above this layer seismic waves travel at a markedly different velocity than they do below it. This discontinuity is so widespread, occurring beneath all of the continents, that it has received a special name: the Conrad Discontinuity. Ordinarily, a geophysicist would expect to find a significant change in rock type when drilling through such a strong discontinuity. It was widely expected that, at the Conrad Discontinuity, drillers would ... the granitic rocks typical of the continents changing suddenly into basalt, which is thought to make up the lower reaches of the earth's crust. However, when Soviet drills pierced the Conrad Discontinuity below the Kola Peninsula, they found no such switchover to basalt at all. In fact, they hadn't even found it when they penetrated to 12 kilometers. This was a shocker. Now, no one knows what the Conrad Discontinuity represents. It doesn't signal a change in rock type; neither is there a fault or boundary of any kind. It is important to find out what is wrong here, because much of modeling of the unseen structure of the earth's crust depends upon a realistic interpretation of seismic records. (Monastersky, Richard; "Inner Space, ...
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... humans-in-europe controversy Astronomy Direct observations of hyperion's chaotic motion A NEW QUASAR DISTANCE RECORD: A NEW EMBARRASSMENT Explaining lunar flashes with life-savers Astronomers up against the "great wall" Biology Dna on cell surfaces Really-deep rivers Geology We live atop a chemical retort Australasian tektites coughed up by a moon of jupiter? Microorganisms complicate the k-t boundary Continuity at the conrad discontinuity Geophysics Eyewitness account of cropcircle formation Possible ball lightning in ankara Psychology Solar activity and bursts of human creativity Geomagnetic activity related to mental activity Psychotherapy may delay cancer deaths Physics A WATCHED ATOM IS AN INHIBITED ATOM General A HUNGARIAN UFO ...
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