H. JAY MELOSH: What killed the dinosaurs? And is humanity headed for a similar fate? These questions are addressed by H. Jay Melosh, a Professor of Theoretical Geophysics at the University of Arizona, in this lecture entitled, "Death of the Dinos: Giant Impacts and Biological Crises". With the help of sophisticated computer simulations Melosh presents his "hot" new theory on the KT extinction that wiped out the dinosaurs some 65 million years ago.