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No. 73: Jan-Feb 1991

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Asteroid impact or volcanos?

The debate over the real cause of the terrestrial catastrophism that occurred at the Cretaceous-Tertiary boundary, some 65 million years ago, grinds on. Some physical scientists claim rather imperiously that the dinosaurs and many other species were done in by the impact of a huge asteroid/meteorite. The worldwide iridium spike is conclusive, they say. Many paleontologists and geologists, however, remain unconvinced and prefer widespread volcanism. We have already covered the various arguments in past issues of Science Frontiers; here, we want to advise our readers that a pair of excellent articles by principals in this debate have appeared in Scientific American. Generally speaking, it seems that the proponents of the impact theory are now listening to the other side. For example, multiple impacts are now proposed to account for evidence of the type introduced below. (Alvarez, Walter, and Asaro, Frank; "An Extraterrestrial Impact," Scientific American, 263:78, October 1990. Also: Courtillot, Vincent E.; "A Volcanic Eruption," Scientific American, 263:85, October 1990.)

A spike dulled. The case for a single asteroid/meteorite impact has been weakened by a recent reexamination of the classic exposure of the CretaceousTertiary boundary at Gubbio, Italy. Here, the discovery of an iridium "spike" at the boundary was thought to betoken a sudden, catastrophic, extraterrestrial event. On further study, though, the spike no longer seems so sharp. In fact, it is spread through about 3 meters of sediments at the boundary. Said sediments apparently took 500,000 years to accumulate! This broad smear of iridium no longer seems indicative of a single extraterrestrial impact. (Rocchia, R., et al; "The CretaceousTertiary Boundary at Gubbio Revisited: Vertical Extent of the Ir Anomaly," Earth and Planetary Science Letters, 99:206, 1990.)

Comment. Is it even indicative of multiple impacts? Recall that no one has yet (1990) found a single crater that everyone will accept as evidence.

Reference. Iridium spikes and the supposed Cretaceous-Tertiary impact are to be found in ESB1 in our catalog: Anomalies in Geology. For more on this volume, see: here.

From Science Frontiers #73, JAN-FEB 1991. 1991-2000 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