The K-t extinction 65 million years ago is the best known of the five major extinction episodes since the Cambrian period. A. Collectively, the five major extinction episodes resulted in the elimination of a larger number of species than did all the minor extinction events. B. The K-T extinction eliminated the dinosaurs and ammonoid mollusks but was followed by the diversification of mammals and gymnospermous plants. C. An extreme cooling of the climate could not have caused the K-T extinction of dinosaurs, because, while most dinosaurs depended on environmental heat, some did not. D. The K-T extinction of the dinosaurs is the only mass extinction that has been explained by the impact of a meteorite. E. In1980 Luis Alvarez proposed that the K-T extinction was caused by ecological disasters brought about by the impact of a meteorite striking Earth. F. A high concentration of iridium in sedimentary rocks at the K-T boundary and a large impact crater in the Yucatan Peninsula from 65 million years ago strongly support Alvarez's hypothesis.