DIFFICULTIES IN UNRAVELING CAUSE AND EFFECT OF NON-UNIFORM EVENTS IN EARTH HISTORY: INTERPRETING GLOBAL CATASTROPHE EVENT MECHANISMS

The paradigm-changing discovery that asteroid impact can cause mass extinction profoundly changed our understanding of biotic diversity through time. This discovery also has important astrobiological implications: surely all habitable planets are at some risk from asteroids or comets, and thus must experience to varying degrees impact-caused mass extinctions, just as Earth has. Yet it is also clear that there are intrinsic as well as extrinsic causes of mass extinction, and that in Earth history there are catstrophic events without accompanying mass extinction (the Manicouagan impact event?) as well as extinctions without seeming (or yet discovered)cause. In this talk I will summarize the current understanding about the "Big Five" mass extinctions, and describe known physical and biological factors that tend to obscure cause and effect relationships in the stratigraphic and paleontological record.