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No. 67: Jan-Feb 1990

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Microorganisms complicate the k-t boundary

Ancient bacteria, it appears, have tampered with the K-T (Cretaceous-Tertiary) boundary of some 65 million years ago. A key marker of this boundary is a thin "spike" of iridium that is found worldwide, and which was supposedly deposited by the asteroid impact that helped finish off the dinosaurs. For many scientists, the asteroid-impact scenario has become a "non-negotiable" brick in the Temple of Science. The problem they have faced is that the iridium layer is variable in thickness and concentration from site to site. Sometimes iridium can be detected well above and below the K-T boundary. This variability has tended to undermine the asteroid-impact theory.

Recent experiments at Wheaton College by B.D. Dyer et al have demonstrated that bacteria in ground water can both concentrate and disperse iridium deposits. In other words, bacteria could smear out an iridium spike, perhaps partially erase it, or even move it to a deeper or shallower layer of sediment.

(Monastersky, R.; "Microbes Complicate the K-T Mystery," Science News, 136: 341, 1989.)

Comment. An obvious question now is how bacteria might have affected other chemicals, such as oxygen and carbon isotopes, widely used in stratigraphy.

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