Plate Tectonics is the combined theory of Seafloor Spreading, Paleomagnetism, and continental drift. The theory states that continental plates rupture, drift, and eventually collide, creating mountain belts, islands, volcanic activity, etc.
The Earth is made up of four main layers. Starting from the center, these are the inner core, which is a solid mass; the outer core, which is made up of liquid; the mantle; and the crust, on which we all walk. The mantle is then further divided, again from the center, the Mesosphere; the Asthenosphere; and the hard Lithosphere. Between the crust and the lithosphere there is a small, thin layer where the plasticity of the Earth changes. This is called the Mohorovicic Discontinuity. The discontinuity is at the very bottom of the crust.
The lithosphere of the Earth is made up of many different plates, or separate sections. There are 8 main plates, which are more than 1000 miles across, and numerous smaller plates, which are less than 100 miles across. The 8 main plates are the African, Arabian, Eurasian, Gorda, Indian-Australian, Nazca, North American, and Pacific plates. Many more plates also exist.
These plates float on the asthenosphere, or the middle level of the mantle. Convection currents in the mantle cause the plates to move. These currents make the asthenosphere to move up and bump the plates, which causes the plates to move. Scientists have devised two ways that the currents could be moving. One is that only the very top level of the asthenosphere is moving, and that is causing the plates to move. The other theory is that the whole asthenosphere is filled with these currents, and this is what is causing the plates to move.
The convection currents cause the plates to move in three independent directions; they are: extensional, transform, and compressional. Extensional, also known as the subduction zone, is the area between two plates when they move apart. That area is also called a destructive plate zone. When plates move along side each other in opposite directions, it is called transform. The last way plates move is called compressional. Here the plates are moving against each other head-on. The area where they are moving against each other is also called a constructive plate zone.
The areas where two or more plates come together are known as faults. There are three types of faults: the normal fault, the reverse or thrust fault, and the strike and slip fault. In a normal fault, one plate moves up and to either the left or right, and the other plate moves down and in the opposite direction. The two plates move toward each other, and one of the plates moves down while the other moves up in a reverse or thrust fault. The strike and slip fault is when the two plates are moving toward each other and along side each other in opposite directions.
When the plates move apart or together, it causes pressure to build up. When the pressure comes to a maximum point, it explodes. In this simple way earthquakes are created. An earthquake is the shaking and trembling of or sudden movement of the earth at a certain point.
Earthquakes can also cause tsunamis, which are huge tidal waves. Tsunamis are so large, that they can sometimes reach the height of a six story building. They occur along coastal or beach areas.
The movement of the plates also causes volcanoes. Volcanoes are points on the Earth where pressure has caused magma, or melted rock, to come pouring out of cracks between the plates, on to the Earth. The magma, called lava once it reaches the surface of the Earth, usually comes pouring out of cone shaped mountains.
There are a variety of actions caused by Plate Tectonics that are much too slow to be recognized immediately. Unlike the earthquakes and volcanoes, which don't take very long to form and are visible as soon as they form, continental shifting and the creation of mountains, valleys, or even continents themselves takes millions and millions of years to become visible. This is explained by the theory of plate tectonics in a simple way.
The Plates are moved by convection currents, as said before, but there are also a variety of other factors that affect the movements of the plates. Gravity, the rotation of the earth, and other such things are also major factors. The plates shift due to this, and then they run, crash, collide, or slowly ooze all over each other at theslow rate of 4 inches of movement per year.
The theory of Alfred Wegener's was that the plates, separate broken pieces, did move, and that they moved on top of the mantle. The theory spoke of the solid inner core, the molten liquid nickel and iron of the outer core, and of the plasticity of the slow-moving mantle.
There has also have been a variety of other scientists that have donated their knowledge to this field.