Dinosaur Extinction: The Asteroid Theory While several theories exist as to why dinosaurs became extinct at the end of the Cretaceous period, most sci- entists agree that their end came about due to a cata- strophic event. One theory is that an asteroid hit the Earth; this theory is known as the asteroid theory. In the 1970s, Walter Alvarez was studying soil composition in a deep layer of Earths crust in Italy. He found high levels of an element called iridium, levels that were almost 20 times higher than expected. Iridium is quite rare on Earth but is common in asteroids and comets. His findings, and those of oth- ers in over 50 different locations, support the theory that an asteroid hit Earth about 65 million years ago. The theory proposes that the asteroid hit with such speed and force that a large hole opened in Earths atmosphere as well as in the ground as it hit. The force of the impact caused a huge dust and debris cloud to cover the planet, which prevented the suns rays from reaching the Earths surface. The lack of the suns energy would have had two devastating consequences to life on Earth. First, Earths tempera- ture would have plummeted, likely to below freezing. Second, the plants and other organisms that used photosynthesis as a means to obtain and store energy would have died. When the plants died off, larger crea- tures that ate plants (herbivores) would no longer have a food source, leading to their deaths. As the herbivores died out, the carnivores (meat eaters) that relied on the herbivores for food would also have died out. And with plants unable to perform photosynthesis, the amount of oxygen available for breathing would de- crease drastically. Therefore, dinosaurs and other animals that went extinct following the Cretaceous period likely died from a lack of food and a lack of oxygen. #biology AIU Alumni Association
Posted on: Sun, 01 Dec 2013 05:54:51 +0000
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