Plate tectonics is a theory which states that Planet Earth's lithosphere (the crust and the upper mantle) is made up of solid plates which float on an underground ocean of magma. These plates are proven to move around. This movement results in earthquakes in the short term, and the movement of continents over hundreds of millions of years.
Tectonic plates can range from the very large-such as the Eurasian Plate, which includes all of Europe and Asia and large chunks of the Arctic Ocean and South China Sea. They can also be small, which includes the part of the Atlantic surrounding the Caribbean islands and a small part of Central America. These plates touch each other at plate boundaries. There are three different types of boundaries.
Transform boundaries are places where the edges of the plates grind against each other. These boundaries are known as fault lines. Sometimes this grinding is gradual and slow. Often, the edges can catch against each other, which results in force building up along the fault. The plates keep straining against each other until the forces become too great. The strained edges skid against each other violently releasing the force and causing an earthquake.
Divergent boundaries are the second type of boundaries. These are often found on the ocean floor and are called mid-ocean ridges. They look like mountain ranges with trenches in the center when looked at from above. At divergent boundaries, the plates are moving away from each other creating trenches. Underground magma rushes up to fill the gap and rises to the sea floor. There it cools into the stone forming the Earth's crust. This newly-formed crust slowly moves away from the ridge as the continents drift, and more crust is formed behind it. This is known as seafloor spreading.
Convergent boundaries are the third type. At these points, two plates are moving towards each other. One plate is pushed underneath the other and into the ocean of magma under the Earth, where it likely melts into magma over time. The second plate is scrunched as it is pushed on top of the first, and often forms mountain ranges. The moving of one plate under the other is known as subduction.
Both divergent and convergent boundaries can lead to volcanoes forming.
The theory of plate tectonics was first hypothesized by meteorologist Alfred Wegner in 1912, though he called it continental drift at the time. He noticed that some continents seem to have coastlines which could fit into each other like puzzle pieces. The east coast of South America and the west coast of Africa are an example of this. There was also archeological evidence, like the fact that many fossils from the same time-period, and of the same species, were found across South America, Africa, and India.
This led Wegner to hypothesize that all the continents on Earth had at one point formed one supercontinent (now called Pangea), and had split up over time due to some mysterious force. He was not the first to have come up with this, but his hypothesis was the most complete at the time. His hypothesis was largely rejected by the scientific community, because he could not find a force which would move the continents around-and nothing just moves by itself. Continental drift only grew to acceptance in the 1960s as scientists discovered mid-oceanic ridges.
It has since been hypothesized that tectonic plates move because of activities in the ocean of molten rock flowing underneath them. The continents sitting on top of these plates are along for the ride, moving at an average of one to two inches per year, about as fast as fingernails grow.
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