How did the Cretaceous world end?



Factors related to evidence of a major impact on the earth by an extraterrestrial body, at about the time of the close of the Cretaceous period, have been the center of discussion at a number of recent symposia. An example is the one entitled ‘Terminal Cretaceous Extinction: A Comparative Assessment of Causes,’ held at the annual meeting of the American Association for the Advancement of Science, Washington, D.C., in January 1982. Another was simply ‘Terrestrial Impacts and C-T Extinctions,’ held at the Thirteenth Lunar and Planetary Science Conference, Houston, Tex., March 1982.

The possibility that an impact may have caused global-scale extinctions of terrestrial and marine life was the main reason for organizing the conferences, but the focus that emerged was on the geochemistry and geophysics of the impacts themselves. A possibility is that the impact occurred in an ocean, resulting in some rather major consequences, including oceanic temperature changes of several degrees Centigrade, an earthquake that would rate magnitude 12 on the Richter scale, and a tsunami, initially about 5 km high, that would have traversed the globe, inundating all low-lying continental areas on the earth within 27 hours.