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Plate Tectonics
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The evidence
of sea floor spreading changed the way scientists looked at the surface of the
earth. Building upon what they had learned from the magnetic records of the
rocks, they developed the theory of plate tectonics.
The Theory of
Plate Tectonics
Basically the
theory of plate tectonics says that the earth is separated into 20 or so large
sections called plates. These plates are about 70 kilometers thick. These
plates sit atop the lithosphere, which is the solid outer shell of the earth.
The crust and the upper mantle are part of the lithosphere. The plates are
rigid and move over the softer asthenosphere of the mantle. This part of the
mantle is partially melted.
Plate
Boundaries
Plate
boundaries are the regions where one plate ends and another begins. There are
three types of plate boundaries.
 Spreading
Boundaries
These are
plates boundaries that are moving apart. Iceland, an island along the
Mid-Atlantic ridge was formed these way. Basically the magma that pushes up
forms new crust as it spreads the existing plates.
Colliding
Boundaries
As the name
implies, these boundaries are formed when two plates collide. When the two
plate bump one plate is absorbed in the mantle of the other. Heat and pressure
when these plates collide causes volcanoes and earthquakes.
Fault
Boundaries These type of boundaries occur when plates rub against each
other. These fault boundaries are seen as cracks in the earth's surface. The
San Andreas Fault in California, where I live by the way, is an example
of a fault
boundary.
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