From this discovery he deduced that the Atlantic must be expanding from its center as molten rock from the mantle underneath seeps through fissures along the Mid Atlantic Ridge. The Marianas Trench off the coast of Japan). These trenches extended down over 11km (e.g. Second, he discovered that (conversely) the deepest parts of the ocean were actually very close to continental margins in the Pacific. The Mid Atlantic Ridge that runs vertically along the ocean floor and is thousands of kilometres in length) that were up to 1.5km higher than surrounding crust. First, he found what are now called "Mid Ocean Ridges" (e.g. During his service in the US Naval Army in WWII, Hess had access to SONAR technology, which he used to map the sea floor in a series of surveys. It wasn’t until a while later that another geologist, Harry Hammond Hess, also saw similar observations in the ocean floors. Wegener’s last contribution was just before his death, in which he found that shallower oceans were younger. What let Wegener down was his proposed mechanism he suggested that the movement was a result of centrifugal force from the Earth’s rotation, or tidal effects from the moon. He presented his ideas to the German Geological Association in 1912, and wrote a book titled ‘The Origin on Continents and Oceans’ in 1915. However, Wegener deduced that the continents must have once been connected in a single super continent (Pangaea), and from this mass the continents drifted apart. These enormous portions of land, which would spontaneously rise and fall out of the ocean floor, were suggested to exist long enough to that they gave flora and fauna enough time to move around the globe. The best received theory was the idea that ‘ land bridges' rose and fell randomly during Earth’s geological history. This also applied to fossil records, including the fresh-water reptile, Mesosaurus (found across South Africa and southern South America), the land reptile Lystrosaurus (found in a band across current India, Antarctica, and central Africa).Īt the time, some of the most prominent theories were that species evolved independently from one another, or that they swam across oceans to get to their current locations. It was shown that 2 billion year old rocks were continuous from one continent to another when placed side by side. Wegener went on several expeditions on both sides of the Atlantic Ocean to analyze rock type and fossil distribution, and he found a very significant ‘matching’ between the East and West sides of the Atlantic Ocean. He noticed that, at the continental shelves, all the large Earth masses fit nearly perfectly. His first ideas came from noticing that the continents of the Earth fit together very closely - but not along their coastlines (this is because of erosion/weathering). In his time, Alfred Wegner (1880–1930) was known for his work in meteorology and polar research, but today he is best remembered for his additions to the development of continental drift theory. Today we almost take for granted our knowledge of how the Earth’s crust shifts and regenerates on a continual cycle but the theory of plate tectonics wasn’t widely accepted until the 1960s! The concept of Plate Tectonics was first coined by the German geophysicist Alfred Wegener back in 1915, but several ideas of continental drift date back many years before. This branch of geology studies the faulting and folding of the crust along the various boundaries convergent, divergent, subduction, and conservative. The rigid lithosphere is split into 7 major ‘plates’ that slowly move on top of the underlying asthenosphere (mantle). Plate tectonics is the theory used to explain the structure of the Earth’s crust and many of the associated phenomena.
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