No. 37: Jan-Feb 1985
In an apparent reaction to the stampede to climb aboard the extinction-by-asteroid bandwagon, dissenting papers have begun to appear in the scientific literature. For example, Van Valen's list of objections to the hypothesis of asteroid impact at the Cretaceous-Tertiary boundary was reproduced in the last issue of Science Frontiers. Now, in a recent issue of New Scientist, T. Hallam raises still more objections:
If it wasn't an asteroid impact, why the iridium concentration? At least three hypotheses have been proposed to circumvent the asteroid debacle: (1) volcanic activity; (2) a concentration of micrometeorites, thousands of tons of which fall each day, through extreme reduction of sedimentation; and (3) selective enrichment of iridium by an anoxic environment acting upon kerogenand pyrite-rich clay.
In short, some geologists at least do not find the asteroid hypothesis compelling at the moment.
(Hallam, Tony; "Asteroids and Extinction -- No Cause for Concern," New Scientist, p. 30, November 8, 1984.)