Deep Reconstruction

Plate Tectonics

Since the beginning of human kind there has been a cloud of wonder of how our planet was formed. Scientist interested in this field through out the years have developed many different theories to how our planet came about. Before the Twentieth Century, scientists and geologists thought that mountain structures were due to the massive tightening of the earth caused by the gradual cooling of molten rocks. In 1900, American scientist Joseph Le Conte, published an article in the Appleton's Popular Scientific Monthly. He described that the problem in understanding mountain building was establishing the cause of sideways pressure. It was not until 1910, that an American Geologist named F.B.Taylor, proposed the idea of a continental drift. Other scientists dismissed Taylor's idea, because there was just not enough proof. However, Taylor's idea was then backed up by a German scientist named Alfred Wegener. He proposed that the continents surrounding the Atlantic Ocean, Africa and South America fit together like a jigsaw puzzle. His broad range of studies enabled him to incorporate his theory of Plate Tectonics. Wegener, later in 1915 while in the German military published his idea that interpreted how his continental drift theory worked. He proposed that a huge landmass called Pangea, meaning ("all land") existed 200 million years ago. He furthered explained that this super continent began to drift apart very slowly throughout millions of years into what it looks like now. Wegener went on several expeditions through out his life to the continents of South America and Africa. He came back with evidence to support his claim of plate tectonics. Wegener and his expedition brought back rock structures, fossils, and evidence of ancient climates. When it came to rock structures, Wegener looked for the similarities of the rocks found along coastlines and the mountain belts found on the continents. They looked at the mountain belts of the Appalachian Mountains and the Caledonian Mountains in Scandinavia and the British Isles. These two continuous belts contained similar rock structures and the ages of these rocks matched the on both ends of the African and South American continents. Wegener also found evidence of massive climatic changes. He researched and found out that ancient glacial deposits were found indicating that ice sheets covered a large part of the Southern Hemisphere, India and Australia. He furthered explained that the Northern Hemisphere was near the equator supporting the idea of coal deposits being located there. Wegener was more intrigued of the fact that fossilized remains were being found along South America and Africa. Remains of the aquatic prehistoric dinosaur called Mesosaurus were only found in eastern South America and Africa. Plant remains were also being found. For example the fossil fern Glossopteris were found sparingly throughout Africa, Australia, India, and South America. Furthermore, this plant was found in polar climates, supporting his theory of connected landmasses. Organisms like the Australian Marsupials and the marsupial opossums found in the Americas, which have a definite fossil link also supports Wegener's theory. Alfred Wegener's theories were not immediately accepted by the scientific community. One of his faults was that he could not prove how the continents moved across the globe. Even though he was in the right direction, he could not completely and precisely determine how the continental drift was accomplished. Therefore, his theories were dropped. Essentially, Wegener was ahead of his time. It was not until years later that other scientist cleaned up some of Wegener's mistakes and resurfaced the Plate Tectonics theory. Thanks to the study of magnetism a whole new window of scientific evaluations emerged to support the theory of Plate Tectonics. S.K. Runcorn proposed an interesting idea. This was strong evidence that the magnetic poles of the earth had migrated through time, meaning that lava flows had moved and so did the continents. This event is called polar wandering. For a long period of time there was still a lot of questions that needed to be answered about the Plate Tectonics theory. Thanks to technological efforts and the mapping of the ocean floor, it became known that there was an oceanic ridge system. Ocean Ridges are slices in ocean floor that extended for 70,000 kilometers. It was not until 1960, when a professor from Princeton University, Harry Hess, suggested Sea Floor spreading. His idea stated that new sea floor was being spread through mid-ocean ridges. As scientist clashed ideas they suggested that continental drift and ocean floor spreading were incorporated in the theory of plate tectonics. They implied that the outer layer of earth called the lithosphere overlaid another layer of earth called the aesthenospshere. It was later learned that the lithosphere was broken into