![]() The cool oceanic crust is denser than the hot mantle and eventually sinks due to the gravitational pull. Subduction is the process where two plates meet, and the denser oceanic crust is pushed under the other. 4 - Convection currents create movement through friction Subduction and slab pull The liquid rock cools, sinks and the process is repeated.įig. The plate then moves due to friction between the convection current and the crust. However, as it reaches the top, it cannot pass through the crust, therefore moving sideways along the crust. This hot liquid rock rises to the crust because its density reduces. The process of mantle convection involves the heating of the liquid rock in the mantle by the core. The continental crust can have a thickness as great as 100km, whilst the oceanic crust is about 5km thick. The oceanic crust is much denser but significantly thinner in comparison to continental crust. The oceanic crust consists of basaltic rock and other materials predominantly of silicon and magnesium. Continental crust is formed of granite rock which comprises quartz, feldspar and other relatively lightweight material mostly made of silicon and aluminium. This makes them less dense than the mantle. Tectonic plates are able to float on the mantle due to the composition of the rocks within the plates. How do tectonic plates float on the mantle? In the 1940s, scientists theorised that magma fills the gap with rock with new magnetic alignment when the tectonic plates move apart. Scientists analysed the rocks in the ocean ground and found that the magnetic signatures of some rocks were in opposite directions, even though they were side by side. As rocks form and cool, the magnetic grains align in the direction based on the magnetic poles. The theory of tectonic plates is also supported by palaeomagnetism (the study of magnetic rocks and sediment to understand the Earth’s magnetic field). The fact that countries are shaped like puzzle pieces and could fit each other.įig.Coal requires warmer and more humid environments to form. He provided considerable evidence that the continents had drifted, but he was unable to find sufficient reasoning for it. This process is called continental drift. In 1912, Alfred Wegener suggested that the continents of Earth had been separated from one large continent, called Pangaea. The theory of plate tectonics answers questions such as: why the earth’s geography changes, why certain locations are prone to certain hazards, and why some locations have mountain ranges. They also found the epicentres of the earthquakes, making it possible to find the outline of tectonic plates. Seismographs were initially used in World War II to test for atomic bombs. The theory of tectonic plates was proposed in the 1960s when seismographs recorded the vibrations of earthquakes. ![]() Principal tectonic plates Why was the theory of tectonic plates proposed? These are: African, Antarctic, Eurasian, Indo-Australian, North American, Pacific and South American.įig. Tectonic plates are moving relative to each other and are responsible for many hazards such as volcanic activities, earthquakes and tsunamis. Tectonic plates are the sections that divide the lithosphere (the Earth’s outer shell, including the crust and uppermost mantle).
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