The surface of the Earth is broken up into large plates. The Earth is dynamic because of its inner heat, which comes from deep in the mantle where heat, rising and falling inside it, creates convection currents generated by radioactive breakdown in the core. The convection currents move the plates. Where convection currents diverge near the Earth's crust, plates move apart. Where convection currents converge, plates move towards each other. The movement of the plates, and the activity inside the Earth is called plate tectonics. Plate tectonics cause earthquakes and volcanoes. The point where two plates meet is called a plate margin or boundary. Earthquakes and volcanoes are most likely to occur either on or near plate boundaries.
Francis Bacon was one of the first people to propose that the West Coast of Africa and Europe seem to have a jigsaw fit with the Eastern Seaboard of North and South America. But it wasn’t until Wegener put forward his theory that plates moved, that great advances were made into understanding this element of our Earth. It is thought that in the past, Earth had one massive continent called Pangea, 300 million years ago, which has slowly drifted further and further apart.
The first piece of evidence to support Wegener’s theory came from the discovery of the Mid-Atlantic Ridge. Vine and Matthews, who were British Geologists, discovered magnetic lines running parallel to the ridges in the 1960s. These lines corresponded to the times when the Earth’s magnetic field reversed from South to North and so on. Iron particles in the erupting magma either side of the ridge cooled and aligned themselves with the Earth’s polarity at that time. These lines supported a theory by Hess (a geophysicist) on sea floor spreading, which we know exists at the Ridge. Also, by studying the lines, the rates of the spreading could be estimated. This theory has also been supported by more studies of the ages of geology either side of the ridge. Rocks closest to the ridge are up to 10 million years old, and those furthest away are over 156 million years old, on both sides of the ridge.
Fossil evidence is an important part of explaining how continental drift works. There are many examples of fossils found on separate continents and nowhere else, suggesting the continents were once joined together. If continental drift had not occurred, the other explanations would be that the species evolved individually on separate continents, which would oppose Darwin’s theory of evolution. The second explanation would be that the species swam to the other continents in pairs and began to breed to establish a second population.
The surface of the Earth is divided into seven major and eight minor plates. There is the Eurasian plate, the North American plate, the Filipino plate, the Australian plate, the Pacific plate, the Antarctic plate, the Juan de Fuca plate, the Caribbean plate, the Nazca plate, the Scotia plate, the South American plate, the Cocos plate, the African plate, the Arabian plate, and the Indian plate. Each plate is in motion relative to its neighbours, resulting in geological activity at the plate boundaries. It is also possible, though doesn’t occur often, for geological activity to take place in the middle of plates. There are three types of plate margins, divergent, convergent and conservative.
At divergent boundaries new crust is created as two or more plates pull away from each other allowing magma to rise, cool and then new lithosphere to be created. When a divergent boundary occurs within a continent, this forms a rift valley. When it occurs in the middle of the ocean it creates mid-oceanic ridges, a mountain range that lies underneath the ocean. If the magma reaches above the ocean, it creates new land, an example of this is Surtsey, a new volcanic island off the southern coast of Iceland. This activity leads to low magnitude earthquakes and also volcanoes.
At convergent plate boundaries the lithosphere is
