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Plate Tectonics Resource Page
Basic Structure of the Earth
Understanding plate tectonics requires a little knowledge of the earth’s basic structure. If you could slice through the earth, you would find
that it is made up of three layers.
Crust
Mantle
Core
The innermost layer is a very hot core of iron and nickel. The inside of the core is solid and the outside is liquid. The middle layer is the
mantle. It is composed of rock that flows very slowly. The outermost layer is the crust. There is oceanic crust and continental crust.
The crust and the upper part of the mantle (which is cooler and more rigid than the lower parts) together make up the lithosphere. The
lithosphere is broken into huge rocky slabs called tectonic plates. These plates ride on top of the asthenosphere, a hot, semisolid part
of the mantle that lies directly under the lithosphere.
Plate Tectonics
Sometimes when the plates move, they can either collide or bump into each other or one can slide under the other. These are called
convergent boundaries. Sliding under one another is called subduction, and often results in volcanoes. If the crusts collide,
mountains can be formed.
Convergent boundaries
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Subduction
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A second type of plate has a divergent boundary. This is when the plate move apart. The space that this creates is filled with new
crustal material that comes from the molten magma below it.
Divergent boundaries
The third type of movement involves transform boundaries. This is when the plates build up as they try to slide against one another.
Eventually the pressure becomes too great and the plates break apart. This causes an earthquake. A fault line is made.
Transform boundaries
Scientists still have a lot to learn. The better able they are to understand the movement of the plates, the more readily they will be able to
predict earthquakes and volcanoes and ultimately save lives.
Proof of Movement of the Plates
Continental drift is the theory that explains why the landmasses on the surface of the planet have changed over time. There is fossil and
plant evidence of the continental drift. Identical fossils and plants are found on different continents and no where else. This leads us to the
conclusion that the continents were once joined. These plants and animals could have lived on the continents when the continents when they
were connected. Then when the continents divided, animals and plants from one area were stuck in other areas. Scientists believe that the
continents had moved and formed through the movement of tectonic plates.
The Changing Earth
The movement of the plates has caused and continues to cause enormous changes in the earth. Mountains have formed, volcanoes have
erupted and earthquakes have shaken the land. This is all due to plate tectonics.
Earth Motion3: Our Changing Earth
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