Continental Drift and Plate Tectonics

Topics: Plate tectonics, Earth, Seafloor spreading Pages: 7 (2637 words) Published: February 14, 2013
Continental Drift and Plate Tectonics Theory (Part 1a)
Introduction: The Beginning of the “Continental Drift Theory” In the middle of the eighteenth century, James Hutton proposed a theory, uniformitarianism; “the present is the key to the past”. It held that processes such as geologic forces- gradual and catastrophic-occurring in the present were the same that operated in the past. (Matt Rosenberg, 2004) This theory coincides with the theory of Continental Drift that was first proposed by Abraham Ortelius in December 1596, who suggested that North, South America, Africa and Eurasia were once connected but had been torn apart by earthquakes and floods. He also discovered that the coasts of the eastern part of South America and the western coasts of Africa fit together like a jigsaw puzzle and this fit becomes especially prominent as the edges of the continental shelves have similar shapes and thus, appear to be once fitted together. (Figure 1.1 and Figure 1.2) The similarity of southern continents’ geological formations had led Roberto Mantovani to speculate that all continents had once been a supercontinent and was smaller in its volume than it is now. Through volcanic activity, fissures are created in the crust causing this continent to break apart. However, this theory, known as the Expanding Earth Theory has since been proven incorrect. The Theory of Continental Drift

In 1912, The Theory of Continental Drift was intensively developed by Alfred Wegener, who claimed that the world was made up of a single gigantic supercontinent named Pangea since the Permian period, 250 million years ago. It began forming at the beginning of the Carboniferous period, 365 million years ago, when Gondwana collided into Laurussia producing the Appalachian mountain belt in eastern North America and closing in Paleo-Tethys Ocean and modern landmass became exposed to air. Alexander Du Toit then suggested that 145-200 million years ago, in the middle Jurassic Period, Pangea started breaking up into two smaller supercontinents, Laurasia in the northern hemisphere and Gondwana in the southern hemisphere, with Tethys Sea and North Atlantic Ocean separating the two supercontinents. The late Jurassic era began the formation of the Rocky Mountains and Sierra Nevada mountains. In the Cretaceous Period, 65 million years ago, the two supercontinents then began fragmenting into the present seven continents. (USGS, 2012) The Tethys Sea that lay between the two landmasses was subducted beneath Eurasia, forming the lower Atlantic Ocean. Eventually, it disappeared. (Nelson Thomas, 2007) (Figure 2) Wegener proposed that continents were moving at about one yard per century and supported this theory with several points of evidence.

Evidence supporting the Theory of Continental Drift (Alfred Wegener and Du Toit) Alfred Wegener matched up coastlines, and he realized that by fitting the continental shelves together, cratons formed a contiguous pattern across the boundary of South America and Africa. (Lois Van Wagner, 2013) He realized that mountain ranges that ended at one coastline seemed to begin again on another such as ancient mountains in South Africa that align with the mountains in near Buenos Aires in Argentina. (Sant, Joseph, 2012) He discovered earthworms of the family Megascolecina, who are unlikely to be long-distance migrators, were found in soils of all the Gondwanaland continents. (kangarooistan, 2009) This identical species could not have arisen on different continents without some variations. (WiseGeek, 2010) Fossil remains of a prehistoric reptile known as the Mesosaurus had been uncovered on both sides of the South Atlantic coasts, yet the creature was unable to swim across the Atlantic Ocean. (Lois Van Wagner, 2013) Fossils of the land reptile, Lystrosaurus were discovered in South America, Africa and Antarctica. (Sant, Joseph, 2012). He also discovered the fossil plant Glossopteris was distributed throughout India, South America,...
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