(Presidential Address 1993) Demise of the dinosaurs and other denizens II – by combined catastrophic causes?

Abstract

Since Charles Darwin's view of geology, the earth sciences have greatly increased in scope and comprehension of processes shaping the evolution of the earth. This is illustrated by the extensive debate concerning extinction of biota at the Cretaceous/Tertiary (K/T) boundary, including the departure of dinosaurs.Pendulums of opinion on causes of K/T extinctions have oscillated as new geochemical, mineralogical, palaeontological, meteoritical, climatological and geothermal data became available for synthesis and interpretation. Abrupt changes at the K/T boundary promoted concepts of catastrophic extinctions. A meteoritic impact school won early acceptance and _a 'volcanic outburst' school developed by 1985. A third catastrophic school, combining both impact and volcanism gained ground in 1988, some workers invoking impact-triggered volcanism and others coincidental but independent impact and volcanic events.Evidence for major impact and volcanism at K/T time is strengthened by location of impact craters, tektite deposits, diamonds, extraterrestrial amino acids and extensive hotspot volcanism. Craters in the northern hemisphere and more extensive hotspot volcanism in the southern hemisphere may explain geochemical differences in K/T sections. Impact directly triggering volcanism is unlikely. Iridium output from over 35 hotspots can account for lower level Ir over 500,000 years, but the sharp Ir peak could fit an impact source. This paper proposes that combined impact and volcanism best explains K/T boundary events. Such a coincidence of major extraterrestrial and terrestrial catastrophic events is not improbable over geological time, but is not essential for global extinctions, judging from the Permo-Tniassic Siberian volcanism.The dinosaurs succumbed to complex K/T events, but exact reasons for their demise remain uncertain. Selenium increase in their egg shells towards the K/T boundary correlates with increasing pathology of egg protein, shell fragility and reproductive loss. Dinosaurs disappeared, while other terrestrial vertebrates survived. The dinosaurs do not rest in peace but haunt the human realm in fantasy literature.