March 13th, 2008, EAV 7b #1

According to Chernicoff, Fox, and Tanner in What Caused the Extinction of the Dinosaurs, paleontologists are very interested in the factors contributing to the massive extinction 65 millions years ago, including 75% of all live forms on the earth and dinosaurs in particular. Some early hypotheses focuses on single factor, however, other proposed that global environment changes were the reasons. But none of them was able to explain why 75% species were lost and the other 25% species survived. One possible factor, which is agreed among several hypotheses, is the catastrophic collapse of the global food chain preceded the widespread extinction because of the "impact of winter". One group suggested that the massive volcanic eruption sent enormous ashes and gases into the atmosphere. The other group proposed the same phenomenon, yet, trigged by the strike of a meteorite. The third hypothsis combined both as trigger factors for the wordwild food shortage. Although there are numerous evidences demonstrating the correctness of these hypotheses, none of them has attained theory status. Hence, scientists are still searching more evidence to support their hypotheses.