Extinction of Dinosaurs - Essay Example

Extinction of Dinosaurs Introduction Dinosaurs were real animals that once lived on the earth, but they died out about 65 million years ago. Since the very first kind of human did not appear on the earth until about 3.5 million years ago, it is clear that no one has ever seen a living dinosaur. Yet, almost everyone has some knowledge about dinosaurs and can picture what at least one or two kinds of these prehistoric creatures looked like. This information about animals that lived so long ago comes from scientists who have pieced together the dinosaurs ancient world from fossil remains. Fossil remains can be in the form of bones, found either in skeletons or separately; footprints in rock; impressions of skin, also in rock; and eggs. Most of the dinosaur specimens that have been collected are in museums. But at Dinosaur National Monument, near Vernal, Utah, a museum has been built around rocks holding dinosaur bones. (Weishampel, p.1) Extinction of Dinosaurs The disappearance of the dinosaurs is in some ways a great mystery. During the time the dinosaurs lived, many new kinds developed and other older kinds died out. Not all kinds died out at once, but by the end of the Cretaceous period, the last of the dinosaurs had disappeared. Scientists have proposed several theories to explain the disappearance of the dinosaurs. There are two main theories of Dinosaur extinction as follows: 1. The Asteroid Theory In 1980 the asteroid theory was proposed by Luis and Walter Alvarez. This theory is based on the discovery of unusually high concentrations of the rare metal iridium at rock levels close to the level of the last dinosaur remains. Iridium is more common in meteorites than in rocks found in the earths crust. According to this theory, a large asteroid crashed into the earth about the time the dinosaurs disappeared. The force of the collision caused a huge cloud of dust to circle the earth. The dust blocked the suns light for as long as five years. This killed many plants, and without food, the dinosaurs died too. High concentrations of the rare-earth element iridium and other heavy metals, believed to be byproducts of a meteor impact, were found in sediments laid down at the time of the dinosaurs demise. Alvarezs theory was further bolstered when, in 1990, geologists discovered a possible site for an extinction-level impact, a 200 km wide crater in southern Mexico. (Ron, p. 277-279) 2. Male Domination Theory Miller et al. who were experts in the field of chemical engineering presented this theory and concluded that main reason of dinosaur extinction was the exceeded birth rate of males as a result of some specific climatic variation. It was a condition where under the gender of the brood was an outcome of temperature. This theory does not raise any criticism against other theories of dinosaur extinction. They don’t oppose the idea that the stroke of meteorite upon the planet and its responding impacts in the long run to kill dinosaurs, but further elaborate it. They elucidate that among mammals like human beings and other creatures gender is genetically determined in an equal ratio. Whereas, in some cold blooded animals like fish and reptiles, sex determination is based on condition of temperature. If these conditions remain ideal, the male/female ratio can be 1:1. However, changing conditions of temperature may cause a slant towards either of the two genders. Consequently, a slant is towards males may direct a turn down in overall population. They further explain that this mechanism of gender classification is being even presently observed among the crocodiles which are basically alike dinosaurs in terms of both biology and physiology. Thus the idea of dinosaur this way is strengthened. In order to demonstrate the impacts of gender ratio on overall population, the theorists utilized the idea of the “Evolution of Y Chromosome” in mankind and linked it with mathematical techniques. Moreover, even better representation is being proposed toward the search of climatic change impacts upon dinosaurs and their eggs in varied types and sizes. The researchers believe that there was a sudden but extended turn in the climate and was not coped y the dinosaurs and they had an exceeded number of males which ultimately resulted into their extinction. (Miller et al., p.954-964) Other Theories Theory of Geographic Changes This theory suggests that dinosaurs were unable to keep up with the many changes that were occurring on the earth toward the end of the Cretaceous period. During the dinosaur age, the earth was very different from the earth today. The climate was generally warmer than it is in the same part of the world today. Large masses of land were covered with inland seas bordered by swamps. And it was in the waters of the seas and on the banks and swamps beside them that the vast number of dinosaurs lived. (The School Science Review, p. 215) Then very slowly, the geography of the earth changed. As the land changed, the habitats that the dinosaurs were used to disappeared, leaving many dinosaurs homeless. Changes in the land brought changes in the vegetation, and the plant-eating dinosaurs were affected. As the plant eaters began to die out, the flesh eaters began to be short of meat. All these changes in geography, plant life, and climate became too much for animals used to other conditions. (The School Science Review, p. 215) In addition to the asteroid theory and the male domination theory, there are some other theories in this context presented by various researchers from time to time. Supernova Theory It is based on an exploding star, or supernova. This theory suggests that a supernova showered the earth with deadly radiation that killed off the dinosaurs. (Svarney, p. 105) Nemesis/The Death Star Theory This theory suggests the existence of an unseen companion star to our sun. It has been called the death star, or Nemesis. Its theoretical orbit would bring it close to the sun about every 26 million years. When it comes close to the sun, it disturbs the gravitational balance of the solar system causing showers of comets to crash into the earth. This could cause catastrophes including the extinction of the dinosaurs. (Raup, p. 19-26) Planet X hypothesis This hypothesis suggests the presence of an unseen planet in our solar system. Its orbit could also cause comet showers on earth. The result, again, would be periodic extinctions. (Golob and Brus, p. 83) Epidemic Theory This theory states that the dinosaurs died from disease. As land bridges formed between masses of land that were once far apart, it became possible for dinosaurs to migrate. Epidemics could have spread during these migrations. (Stanle, p. 18-27) Flood theory A new breakthrough in China may assist the researchers to establish the exact reason of dinosaur extinction. Paleontologists have excavated more than 7,600 fossilized dinosaur bones near Eastern China closed to the Yellow Sea. The majority of the bones date to the late Cretaceous Period, between 65 million and 98 million years ago. This was the actual time of extinction determined by the scientists. The mentioned collection of fossilized dinosaurs is presently the largest ever exposed in the planet. The bones include tyrannosaurs and ankylosaurs. Though, the bones were all discovered at one spot, the dinosaurs could not have all died there. Geologists predict the dinosaur bones could have been swept together by a flood. (What killed Dinosaurs? P. 1) None of these theories has yet been documented. However, we do know that the conditions that supported dinosaur life changed irreversibly. The huge reptiles that walked the earth for more than 165 million years were not, in the end, able to survive the changes, whatever they were, within the planet or from the outer space. Works Cited Golob, Richards & Brus, Eric. The Almanac of Science and Technology: Whats New and Whats Known. Harcourt Brace Jovanovich, 1990 Miller, David, Summers, Jonathan, & Silber, Sherman. Fertility and Sterility, Vol. 81, No. 4 (April 2004), pp. 954-964. Raup, David M. The Nemesis Affair: A Story of the Death of Dinosaurs and the Ways of Science. Edition: 2, revised, illustrated. Norton, 1999 Ron, Morton L. Music of the Earth: Volcanoes, Earthquakes, and Other Geological Wonders, Perseus Books Group, 2002. Stanle, Steven M. Extinctions-Or, Which Way Did They Go? Earth, Kalmbach Publishing Co. 1991, p. 18-27 Svarney, Thomas E. The Oryx Guide to Natural History: The Earth and All Its Inhabitants. Greenwood Publishing Group, 1999 “The School Science Review”, Science Masters Association, Association for Science Education. J. Murray. P. 215 Weishampel, David B. "Dinosaur." World Book Online Reference Center. 13 April 2009, http://www.worldbookonline.com/wb/Article?id=ar159320 "What Killed The Dinosaurs?" Current Events, 2, eLibrary, Proquest CSA. ROBINSON SECONDARY SCH. 13 Apr 2009. http://elibrary.bigchalk.com Read More