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 found in the sedimentary rocks at the very end of the Craterous. In several places around the world, at exactly 65 million years age, geologists have found large amounts of the metal iridium in clay bands. Iridium is a rare metal that comes only from space. We normally find only very small amounts, which come from the tiny meteorites that land on earth all the time. But there are very large amounts of iridium at the time the dinosaurs died out. Many scientists believe this is good evidence for an asteroid, but the case is not proved.

The next theory for the extinction of dinosaurs is the "Deccan Trap" theory. The Deccan Traps was a massive volcanic eruption that took place just about the time the dinosaurs died. Benjamin Bonnefoy, a French researcher, presented "a study of Indian lava fields that suggested ancient volcanic activity was intense enough to have caused the climate changes believed to lie behind the extinction of the giant lizard" (Suzuki). So much lava was spewed in this eruption that the Himalayan Mountains were formed. Also, enough ash could have been thrown up into the atmosphere in this eruption, that the sun would have been blocked out, killing the dinosaurs, some plants and other animals. Over a time span of several million years, the volcanic activity could have possibly created enough dust and dirt to prevent sunlight exposure which produced drastic climatic changes.

The last theory for the extinction of dinosaurs is a major climatic change. Changes

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