Plate Tectonics Theory Essay

Evaluate how dwelling tectonics possibleness helps our understanding of the distribution of seismic and volcanic events In 1912, Alfred Wegener published his possible action that a single super continent named Pangaea once existed about three hundred million years ago. He proposed that Pangaea then later split into 2 continents of Laurasia in the north and Gondwanaland in the south and that todays continents were the emergence of further splitting of these devil land masses. Where the plates split atomic number 18 know as plate boundaries. Wegeners scheme of continental drift was support by both geologic and biologic designate that these areas were once joined. The geological evidence included the rock sequences in Northern Scotland closely agreeing with those put up in East Canada, indicating that they were laid downward(a) under the same conditions in one location as well as the obvious gigue saw fitting appearance of todays continents, in particular, the gibbosity o f south America fitting into the indent below west Africa.The biological evidence comp rescindd of fossil findings linking divers(prenominal) continents. Fossil brachiopods found in Indian limestones were comparable with similar fossils in Australia and the fossil remains of Mesosaurus were found in both South America and southern Africa. It is unlikely that the same reptile could have developed in both areas or that it could have migrated crosswise the Atlantic. Despite the evidence, Wegeners theory was unable to explain how continental execution had farered. However from the 1940s additional evidence accumulated after the baring of the mid-Atlantic ridge and huge mari dateic trenches. Examination of the ocean change surface either expression of the mid-Atlantic ridge suggested that ocean- nucleotide spreading was occurring. Magnetic surveys of the ocean floor in the 1950s, showed regular patterns of paleomagnetic striping surrounding the ridges. It was discovered that whe n lava erupts on the ocean floor, magnetic domains within iron rich minerals in the lava are aligned with the magnetic field of the earth. This fixes as the lava cools and records the earths signboard at the time of their chill.As the polarity of the earth reverses every 400,000 years, bands of normal and reversed polarity rocks are mirrored on either side of the mid ocean ridges, suggesting that brand-new rocks are being added equ aloney on either side. Surveys to a fault established the age of the rocks and found young ages for places on or adjacent the ridges and much older ages for rock nearer to the continental masses, demonstrating that older rancor is continually being pushed aside bynew sauciness. The discovery of sea floor spreading led to the assumption that the earth must be getting bigger however this was not the case and the discovery of nautical trenches allowed for the conclusion that plates must be being destroyed at different boundaries to accommodate the inc rease in their size at mid-oceanic ridges. Hot muscae volitantes around the core of the earth generate thermal convection currents within the cape which cause magma to rise towards the cheek and then spread before cooling and sinking.This circulation of magma is the driving force of plate operatement. This feat has an effect on all the plates determining their type of limitation from each one with their own lineaments and outleting volcanic and seismic events. Divergent boundaries occur on spreading centers where plates are moving by and new crust is created by magma pushing up from the mantle resulting in oceanic ridges and rift valleys. Where two oceanic plates are moving isolated they gain mid oceanic ridges with their form influenced by the rate at which the plates separate. Volcanic activity occurs along the ridge forming deputizemarine volcanoes which sometimes rise above sea level accommodating fairly gentle sides and oftentimes gentle eruptions. An example of this is located in Surtsey, to the south of Iceland, and Iceland itself. As new crust forms and spreads, transform faults occur at right angles to the plate boundary due to shearing pressure. The parts of the spreading plates on either side of these fault lines may move at different rates do shallow focus earthquakes. Where two continental plates are spreading they produce rift valleys.The brittle crust fractures at sections as it moves apart create a normal fault where hanging wall falls down relative to the foot wall due to tensional stress. A feature of a rift valley is known as a graben which forms when a block of rock falls between two faults and creates the valley floor and also a horst which is formed when a block of rock is pushed up between two faults. This area is associated with volcanic activity as the crust is much thinner than in neighbouring areas. Convergent plate boundaries occur when two plates are moving towards each other. Where oceanic and continental crusts go steady, the denser oceanic crust is forced under the lighter continental plate known as subduction. The down warping of the oceanic plate forms a very thickset ocean trench and the continental plate edge is affected by the reverse fault lines that cause crease of the plate to produce steep rock that forms Fold Mountains. Asthe oceanic crust descends, the increase in pressure can stir up major earthquakes along the line of the sub ducting plate. As it descends further the surroundings become hotter and additional heat from the attrition causes the rock to melt in the benioff zone which begins to rise as plutons of magma. When they ambit the surface they form composite explosive volcanoes.Eruptions can also occur offshore producing volcanic islands referred to as island arcs. Where two types of the same plate meet they create collision zones by which the compression of the two plates results in the folding of the plate to form Fold Mountains. As at that place is little subd uction, there is no volcanic activity however the movement of plates can trigger shallow-focus earthquakes. Conservative plate boundaries occur when two crustal plates slide past each other and the movement of the plates is parallel to the plate boundary. The movement of the plates creates stresses between the plate edges and as they rub past each other the release of encounter triggers shallow focus earthquakes. However as there is no subduction, there is no volcanic activity. The best known example of a right boundary is the San Andreas Fault in California, where the pacific and North American plates move parallel to each other.Volcanic activity that does not occur along any plate boundary can be the result of many another(prenominal) a fault lines and hot floater beneath the crust. Alfred Wegeners theory allowed us to gain insight into the potential creation of our tectonic plates and their boundaries. The evidence provided by wegeners theory and the record of paleo-magnetism upon the ocean floor back up the idea that the tectonic plates are moving. Supported by the theory of convection currents, the movement of these plates helps our understanding of the distribution of seismic and volcanic events by allowing us to rank varying plate boundaries that create different features and as a result cause these events. This explains their distribution, as events such as these are located in areas above plate boundaries, apart from the odd one which can occur above many a fault lines or hot spots caused by the movement of plates.