Tectonic Theories (Essay Sample)

DEVELOPMENT AND HISTORY OF PLATE TECTONICS
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The break up and movement of continents has always been a hot point of debate. As early as 1596, scientists such as Abraham Ortelius speculated on the movement of the continents. It was not until 1912 Alfred Wegener postulated a formidable theory. Unlike his predecessors, Wegener’s theory was significant because the theory provided fossil, paleo-topographical and climatological evidence of similarities in the various continents. His hypothesis was published in his famous compendium Die Entstehung der kontinente und Ozean (The Origin of continents and Oceans) in 1929. This publication came after Wegener noticed a loud congruence between the east coast of South America and the African coastline. Wegener observed that continents had been one large mass that had drifted apart and had been pulled by centrifugal pseudo force as a result of the earth’s rotation. The history of plate tectonics proves that the earth is an unstable collection of matter that undergoes a continuous movement the different tectonic plates.
Wegener’s hypothesis was rejected on various grounds. Harold Jeffrey, a renowned Geologist of his time, did calculations and ascertained that centrifugal forces brought about by the earth’s rotation were not sufficient to move the continents. The work did by Wegener was also refuted because the theory failed to account for earlier magnetic processes. In addition to that, Wegener’s theory failed to provide plausible evidence for the physical processes involved in continental drift. Scientists also argued that masses floating freely in substratum should be in isostatic equilibrium, where gravitational force equals the buoyancy. However, many parts of the earth did not exhibit this equilibrium. The theory also failed to explain why some parts of the earth’s crust had solidified while others were still fluid.
The Plate Tectonics theory is a more modern and refined explanation of continental drift. It describes the process by which plates move across the lithosphere as a result of convection forces. The convection forces are brought about by variations in densities in the mantle. The earth consists of three layers, the crust, mantle and the core. The crust is made of silicates and is divided into oceanic and continental. Continental crust is thicker than the oceanic although it is less dense. The mantle has the lithosphere that is made up of cool and rigid rocks. Most activity occurs at the plate boundaries. There are three distinct plate-boundaries namely: divergent, convergent and transform. In divergent boundary, plates move away from each other and is always accompanied by volcanic activity. There is also sea floor spreading and continental rifting that explains the mid-Atlantic Ridge.
In convergent boundary, plates move toward each other leading to deep earthquakes. In ocean-ocean convergence, the occurrence of subduction leads to volcanic island arcs and deep ocean trenches. In ocean-continent, oceanic lithosphere subducts beneath the continental one and a volcanic arc is formed. In the continent-continent convergence, there is no subduction because the continental crust is less dense. Here, the resultant is mountain building as is evident from the formation of the Himalayas. In transform boundaries, plates slide along faults quickly leading t...