Extinction Essay

2048 words - 8 pages

EXTINCTIONTwo-hundred and thirty million years ago the first dinosaur-like creature roamed the earth. Within five million years it could be considered a dinosaur. They were soon at the top of the food chain. They populated every continent. Then 65 million years ago they vanished. The most powerful creatures ever to live on earth had become extinct.Dinosaurs were not the only victims of this 'mass extinction.' There were many other species that were killed off. During what is known as the K-T extinction (K stands for Cretaceous, T stands for Tertiary), many species and families became extinct. These include all marine reptiles such as plesiosaurs, mosasaurs, ichthyosaurs, and ammonites, swimming and flying reptiles, sea crocodiles, and foraminifera. In addition to that there were many bony fish, sponges, snails, clams, and sea urchins became extinct.Paleontologists have proposed scenarios that could have caused these extinctions. One such scenario involves the growing number of small mammals which ate dinosaur eggs, and therefore caused the dinosaurs' birth rate to drop. The birth rate became smaller than the death rate and the dinosaurs died out. This, however, is not a plausible scenario. This would only account for the dinosaurs, but not all the other creatures of that time. Paleontologists needed to come up with a more plausible and devastating theory that would include the other creatures that died out 65 million years ago.There have been several major theories that have come about that can all be substantiated. Any one of these events, theorized by paleontologists, could have brought an end to the dinosaurs and all the other species that died with them. Since there are many theories about this I will not write about them all. I have chosen the theory about death by Cosmic Collision (an asteroid).In 1980 Luis Alvarez and John Sepkowski Jr., famous geologists, blamed the extinction of the dinosaurs on a large celestial body which hit the Earth 65 million years ago. According to them, an asteroid five miles across blasted through the Earth's crust, and threw up molten rock, ash, and dust. Adding to the support to this theory is the discovery of a layer of iridium in New Zealand, Denmark, and Italy. This layer became known as the iridium anomaly. Remarkably, this layer of iridium was found in sedimen tary rock that is abundant on other celestial bodies. This was too remarkable to be a coincidence, so the research team decided that the layer of iridium must have been caused by space debris which resulted from the collision of Earth and another celestial body. At first, Alvarez's theory was not widely accepted, but as more iridium was found from that period of time around the world, it became the leading theory. Other evidence includes the discovery of stishovite, a mineral created by high heat and pressure. These two minerals were most likely caused by a cosmic collision. Even more stunning, geologists have found a huge crater on the Yucatan...

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