Mass extinction:  a commentary.
Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions.  Although strongly interconnected the four claims are independent in the sense that none depends on the others.  Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies.  An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales.  If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated.  This is line of reasoning can only be considered an hypothesis for testing.  In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth.  The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.
Raup
D M
DM
Department of Geophysical Sciences, University of Chicago, Illinois 60637, USA.
D000818:Animals; D005075:Biological Evolution; D018534:Earth, Planet; D007448:Invertebrates; D019110:Meteoroids; D018543:Minor Planets; D010163:Paleontology; D010507:Periodicity; D016082:Solar System