The Theory of Continental Drift - Essay Example

?Plate Tectonics In 1915, Alfred Wegener, a German geophysicist, published his Theory of Continental Drift to answer why similar plant fossils and geological features were found on either side of the Atlantic. However, Wegener was unable to explain the mechanism that allowed land masses to move and his theory was discredited by his peers. It was not until the 1960s that scientists were able to explain the mechanism, finally answering Wegener's problem, which was that solid continental and oceanic plates floated on a molten rock bed. This became known as Plate Tectonic Theory and has become widely accepted by geologists. This paper explores both Wegener's theory and Plate Tectonic Theory, explaining how the Earth's land masses move and the construction and destruction of the Earth's crust and the features of plate tectonics as understood today. Plate Tectonics In 1911, Alfred Wegener (1880-1930), a German geophysicist, was intrigued to explain similarities in fossils of plants and animals found on either side of the Atlantic . Scientific thinking of the time was that continents were joined by land bridges that were now submerged by the ocean. However, Wegener also noticed the similar shapes of the coastlines of the continents and similar geology that supported his theory of continental drift. He postulated that these land masses may have been joined together at one time and that the original land mass, called ‘Pangaea’ (after the Greek for ‘all of the Earth’) has broken up and drifted apart . Wegener found evidence to support his theory of continental drift. He noticed that land masses fitted together with adjacent land masses. He also found signs of glaciation on the plains of Africa and coal deposits, usually associated with tropical areas, found near the North Pole. He also found fossils of exactly the same prehistoric species located in the same areas if the land masses were joined together, see Figure 1. . Figure 1: Locations of spread of fossils across continents before they broke up . Wegener did not fully explain what caused continental drift. He suggested two hypotheses, one that continents moved due to the forces associated with the rotation of the Earth and a second, which suggested continents moved due to tidal attraction of the Sun and Moon . However, both of these forces were too weak. These hypotheses were ridiculed by other scientists because no answer could be provided to explain how continental masses move . The original theory of continental drift was discredited, helped along by the growing anti-German feeling in the 1910s and 1920s and Wegener’s lack of scientific knowledge of geology . Wegener’s principle of continental drift was discredited but it did pave the way for scientists to explore why parts of the Earth’s surface have moved over time . Paleomagnetic studies, which measured the Earth's past magnetic field, found that the magnetic North Pole seemed to wander around the Earth over time . Evidence from seismometers, originally installed to monitor nuclear testing by the 1960s, found that geological phenomenon, such as volcanoes and earthquakes, were mostly found along the edges of tectonic plates . In addition, scientists found that rock crystals in certain rocks varied from normal to reversed polarity depending on when the rock was formed and solidified . These patterns mirrored themselves either side of the mid-oceanic ridge in the middle of ocean basins and rock samples were older the farther from the mid-oceanic ridge . All this evidence answered the problem Wegener was unable to; that solid continental and oceanic plates of the Earth’s crust, or lithosphere, ‘float’ on molten viscous rock called the asthenosphere, which forms the basis of Plate Tectonics Theory . Based on the Plate Tectonics Theory, plates adjacent to one another must move. Plates can move apart (forming a divergence plate boundary), together (forming a convergent plate boundary) or slide or grate against each other (creating a transform fault boundary) . A diverging plate boundary occurs when plates begin to separate, creating a rift, (see Figure 2 for a summary of all forms of plate tectonics). Hot magma rises from deep within the mantle pushing up the plate's crust forcing the continent to break up . Earthquakes and lava flows are often seen during the creation of a diverging plate boundary . Plates are continually being made and destroyed. New boundaries are created by rifts and plate boundaries are destroyed, by subduction, resulting from convergent plate boundaries . As the plates move towards each other, one plate slips below the other, which is 'lubricated' by the water of the ocean. An island arc system is formed as molten magma rises to the surface to create volcanoes that may eventually grow out of the ocean creating islands along the boundary . If subduction occurs between two continental plates, vast mountain ranges can occur and earthquakes may occur . The Himalayas were created following the collision of the Tethys oceanic crust and the Asian continent 55 million years ago . If subduction occurs between a continental and oceanic plate, deep trenches form, and earthquakes and volcanoes may occur . Figure 2: Visual summary of Plate Tectonics Two features commonly associated with plate tectonics are earthquakes and volcanoes. The forces exerted by moving plates can be tremendous. The strain and pressure can be built up over a long time and released within a matter of minutes in the form of an earthquake. Often earthquakes are unpredictable and cause significant damage to buildings and loss of life . Volcanoes occur along divergent and convergent plate boundaries, areas of continental extension and in areas, known as hotspots, located away from the plate margins . Volcanoes occur as mantle plumes rise from some 1,800 miles beneath the Earth’s surface and burst through, pouring lava out onto the Earth’s surface . The force of magma plumes have been suggested as being responsible for breaking up the Pangaea supercontinent . References Read More