A theory that the Earth outer shell consists of a series of rigid plates known as the lithosphere. These plates move in response to convection currents within the mantle. The interactions of the plates at their boundaries yield earthquakes, volcanic activity, ocean trenches, island chains, mountain ranges and other features.
Tectonic plates are sections of the Earth's solid crust that “float” on top of the mantle.
The mantle contains hot molten rock (magma) heated by energy from the earth's core
The earth’s crust is made up of seven main tectonic plates and numerous smaller plates.
There are two main types of tectonic plate.
Oceanic plates are relatively thin (about 6-10 km) and contain very heavy (dense) rocks such as basalt.
Continental plates are considerably thicker (35-40 km) but contain lighter (less dense) rocks such as granite.
The plates fit together like pieces of a large jigsaw. Tectonic plates meet along four main types of plate boundaries.
The tectonic plates are in constant motion travelling at a few centimetres per year.
The ocean floors are continually moving, spreading from the centre and sinking at the edges.
Where plates meet, huge forces build up causing earthquakes and volcanoes and the formation of fold mountains and deep-sea trenches.
Have a look at the different plate boundaries in the world and what type of features they create:
http://geology.com/plate-tectonics.shtml
The video below shows how the continents have drifted apart over millions of years. This theory is known as Continental Drift.
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