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Tectonics - The branch of geology that
deals with regional or global structures and deformational features of Earth.
Plate tectonic theory was developed in the mid 1960s.
The lithosphere is made of the Earth's crust
and part of the upper mantle. It is rigid, but the underlying
asthenosphere is like a very thick liquid.
There are 7 very large plates and about a
dozen small plates that make up the crust of our Earth. Plates move
because they are sliding over the more mobil aethenosphere. Plates
generally move at a rate of 1 cm to 10 cm each year.
Three types of plate boundaries are known to
exist.
Convergent - Intense compression ultimately
rumples the lithosphere and builds folded mountain belts. When two plates
converge, one tips down and slides beneath the other. This is called
subduction.
Divergent - Plates move apart. Here,
magma often rises to the surface, especially on the ocean floor.
Transform - Plates horizontally slide past each
other. Earthquakes are common here, but volcanoes are not.
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