There have been many different theories of how the dinosaurs went extinct. These theories were the asteroid theory, the volcanic theory, and the marine regression theory. The marine regression theory does not exclude the existence of an asteroid impact, but the impact is determined to be extinction to an already decreasing ecosystem. The volcanic theory suggests that the iridium surplus found in the Yucatan Peninsula might have come from the intense volcanic activity. This theory believes that the dinosaurs went extinct from the volcanic activity because iridium is more frequently found in the earth's mantle. The asteroid theory states that sixty-five million years ago an asteroid hit the Earth and caused the extinction of the dinosaurs. This theory is believed because of the huge amounts of iridium found in the Yucatan Peninsula were from within the asteroid, and when it crashed into the Earth. In recent years, the evidence suggests that the theory of dinosaurs becoming extinct by an asteroid collision seems to be the most accurate theory.
             Many dinosaurs became extinct before the mass extinction, towards the end of the Cretaceous period. During the end of the Cretaceous period, it was the time of continental drift and volcanic activity. Pangaea was separating into the continents we see today, and many mountain ranges were formed, from this movement. During the middle of this period, sea levels also rose and covered about one-third of the land area. Toward the end of this period, the sea levels dropped, which exposed many of the continents, and the Earth was becoming colder.
             Luis and Walter Alverez made a study of the rocks around the K-T boundary in Gubbio, Italy. While researching, they found an unusual layer of clay. The clay showed high levels of iridium, which was thirty times more than the normal level in this area of the K-T layer. There are only two sources of iridium, which are from outer space, and the Ear...