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No. 67: Jan-Feb 1990

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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 find 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," Science News, 136:266, 1989.)

Reference. Large-scale structural anomalies of the earth's interior are classified under ECD in the catalog: Inner Earth. This book is described here.

From Science Frontiers #67, JAN-FEB 1990. 1990-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987