K-T Transition Greenhouse and Embryogenesis Dysfunction in the Dinosaurian Extinctions

Abstract

The dinosaurs became extinct 65 million years ago during the K-T transition mass extinction that defines the Cretaceous-Tertiary boundary. Debate exists over whether the extinctions were caused by asteroid impact or Deccan Traps volcanism. Impact-induced global blackout and refrigeration, known as an “impact winter,” and volcanism-induced climatic warming, known as a “greenhouse,” have both been invoked as killing mechanisms. Temporal linkage of a physical phenomenon with a mass extinction does not establish causality. A killing mechanism preserved in the record must be isolated and coupled physiologically to the organisms that became extinct. The K-T record lacks definitive evidences of an impact winter. Carbon-cycle perturbation and warming are reflected in the δ13C and δ18O records. Several K-T phenomena (marine transgression, reduced photosynthesis of terrestrial and marine floras, reduced weathering rates, K-T boundary eruption of 90 percent of the Deccan Traps lavas, and possible K-T asteroid/comet ...