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Introduction

To what extent can the theory of plate tectonics explain global distribution of seismic and volcanic activity? The global seismic and volcanic activity is concentrated along the margins of the earth?s plates, which are broken pieces of the crust and are moved by convection currents that are caused by heat rising and falling inside the mantle generated by radioactive decay in the core. This movement of the plates and the Earth?s inner activity is called plate tectonics and can cause seismic and volcanic activity. However, earthquakes and volcanoes also occur within the plates rather than their edges, an example of which is the Hawaiian volcanoes that occur above a stationary hot spot beneath the Pacific plate. In the late 1960s the theory of plate tectonics was developed by Alfred Wegener and provides an explanation for the Earths tectonic behaviour, particularly the global distribution of mountain building, earthquake activity, and volcanism in a series of linear belts. However, before the theory was developed people had noticed that the continents either side of the Atlantic Ocean seemed to nearly fit together. In 1912 Alfred Wegner published the theory of continental drift suggesting that the continents used to be joined together in an ancient supercontinent which he named Pangaea. He then proposed that it later split in to two continents- Laurasia in the north and Gondwanaland in the south, which further split forming our current continents and at some point these land masses had drifted apart to their current positions on the globe. ...read more.

Middle

The Earth?s magnetic field is thought to be due to the different rotation speeds of the mantle and outer core. Earthquakes often occur in broad uneven belts along plate boundaries because most are related to plate motion. However, the earthquakes that do not occur along plate boundaries are associated with the reactivation of old fault lines, such as the September 2002 earthquake in the Midlands which measured 4.8 on the Richter scale. It is believed that it was caused by the movement along an old fault line called the Malvern lineament. It has also been suggested that human activity could be the cause of some minor earthquakes due to the impacts of building projects; including the construction of large reservoirs in which the water puts pressure on the surface rock or in deep mines where they gradually start to cave in or sink. Volcanoes form when magma rises through cracks or weaknesses in the Earth?s crust causing pressure to increase inside the Earth. Once the pressure is released such as by plate movement magma explodes to the surface, this is called a volcanic eruption. The lava then cools to form a new crust. Most volcanic activity is associated with plate tectonic processes and is mainly along plate margins. Therefore, volcanic activity occurs along oceanic ridges where the plates are moving apart, (an example of this is the mid- Atlantic ridge where Iceland was formed by volcanic activity) ...read more.

Conclusion

Also at subduction zones the convection currents can pull slabs of Oceanic crust down into the mantle. The theory of plate tectonics sufficiently describes seismic and volcanic activity that occurs along plate boundaries, practically localized movement and it is supported by several pieces of both geological and biological evidence, such as fossil remains of the Mesosauras reptile have been found in South America and Southern Africa. This is because it is very unlikely that this reptile could have migrated across the Atlantic or developed in both places. Furthermore, it provides an explanation for the distribution of majority of earthquakes and volcanoes so can explain the global distribution to a high extent. However, it does not take into account every single one and can be argued that the theory?s extent is weak because it does not provide an adequate explanation of the start of continental movements or the initial plate boundaries. It also assumes that the Earth is billions of years old and the time frame for the continents movements is dependent on various periods in of the earth?s history, which can be classified differently. On the other hand the theory of plate tectonics provides a basis for analyse of present events along plate boundaries and the prediction of future events including their size and scale. Overall, the theory of plate tectonics explains the global distribution of seismic and volcanic activity to a high extent because the majority of events occur along the plate boundaries. ...read more.

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