Number 106 (Story #2), December 14, 1992 by Phillip F. Schewe and Ben Stein|
AN ASTEROID IMPACT MAY HAVE CAUSED THE MASS EXTINCTION that occurred at the boundary between the Permian and Triassic periods 250 million years ago, said Michael Rampino (212-998-8995) of NYU at the AGU meeting. He asserted that he has found evidence---in the form of gravity anomalies and certain rock deposits---for such an impact in the South Atlantic, in an area where, many scientists believe, South America, Africa, and other land masses fit together in the primordial supercontinent called Gondwanaland. Rampino claims that the gradual breakup of Gondwanaland into present-day continents may have been initiated by the catastrophic impact. Another scientist at the meeting, Verne Oberbeck of NASA/Ames (415-604-5496) also believes an impact may have sundered Gondwanaland and that, in general, impacts should be given more credit for shaping earlier Earth geology. In particular, he believes that the small rock sediments called tillites, usually thought to result from the grinding and plowing action of glaciers, may in part be debris from impacts. Consequently, Oberbeck suggested, there might have been fewer glacial periods than is usually believed. Rampino went so far as to say that all tillites are of impact origin. Unlike the theory that describes the KT (Cretaceous-Tertiary) catastrophe 65 million years ago (when the dinosaurs became extinct) in terms of an asteroid impact, the notion that the PT catastrophe was caused by an impact or that tillites result from impacts is anything but a majority opinion; indeed, many scientists at the meeting were skeptical about Rampino's and Oberbeck's ideas. Thomas Crowley of the Applied Research Corp. (409-846-1403), a paleo-climatologist, said that his reaction to the proposed impact origin of tillites was one of "considerable disbelief, bordering on incredulity." For one thing, he said, tillite deposits are too extensive over time and physical extent to have been caused by an impact.