Extinction of Dinosaurs

Extinction of Dinosaurs Two-hundred and thirty million years ago the first dinosaur-like creature roamed the earth. Dinosaurs were a very successful and diverse group, dominating the terrestrial environments of the earth for 160 million years. The apparently sudden mass extinction of dinosaurs marks the boundary between the Cretaceous and Tertiary periods. Though there is not one definitive explanation to explain dinosaurs' extinction, there are various theories that attempt to account for the mystery of their extinction. The theories that explain their extinction at the end of the Cretaceous period are the asteroid, the volcanoes, and the major climatic changes.
The most popular "disaster theory" for the extinction of the dinosaurs is that the Earth was hit by an asteroid or a comet 65 million years ago. The impact was proposed by a Professor of geology from Berkeley, California, Walter Alvarez. Alvarez's conclusion about the extinction was "A giant meteor had struck down the world of dinosaurs" (Bakker 432). Alvarez believed that "…a huge meteor (or asteroid), smashing into the earth at the end of the Cretaceous, would blanket an immense area of the earth with its extraterrestrial cargo of iridium because the explosion of the celestial mass would send up vast clouds, full of iridium-rich dust" (Bakker 432). An asteroid called Chicxulub hit the earth creating a 150 mile wide crater near the Yucatan Peninsula in Mexico. The asteroid is thought to have weighed 4 million tons. When it hit the Earth it would have formed a crater 60 to 90 miles (100 to 150 km) wide. The asteroid would have exploded deep down in the crater and shot out up to 400 trillion tons of rock and dust. The dust would have blocked the light from the sun. The asteroid might also have heated the air and produced acid rain. The effects of this kind of impact would have killed off many forms of life. However, no crater of the right size and age has been found. The best evidence for the asteroid is