Plate Tectonics

Plate Tectonics

The top layer of the Earth’s crust is covered by giant pieces called tectonic plates. There are seven large plates and several smaller ones, all moving very slowly at different speeds (2cm to 10cm a year), and in different directions. The plates under the ocean are called oceanic plates. The ones under continents are called continental plates.

The place where two plates meet is called a boundary, and it is at these boundaries where new crust forms and old crust is returned to the core to be melted again. This cycle of crust forming and later melting down in the core takes about 100 million years.

There are different ways in which plates meet:

At some boundaries, called Divergent Boundaries, the plates move away from each other, and the very top layer of the crust (called the lithosphere) breaks apart, and the space that forms between them sinks down into the second layer of the crust (called the asthenosphere) to form a valley called a rift. Liquid rock called magma seeps up from inside the earth to fill cracks. It hardens and becomes a new part of the Earth’s crust.

A rift valley in Iceland: photograph © [2007] Jupiterimages Corporation

At other boundaries, called Convergent Boundaries, two tectonic plates come together, pushing against each other. One plate is forced upwards, causing mountain ranges, including volcanoes, to form. The other plate is forced downwards and its edge eventually sinks into the core and melts. Large and small earthquakes occur along these boundaries.

volcano: photograph © [2007] Jupiterimages Corporation

At Transform Boundaries, two plates slide against each other as they move past in different directions. As they slide past each other, neither is destroyed or pushed up or down. The movement causes energy to build up, which may be released as earthquakes.

The study of these movements and formations by geologists is called Plate Tectonics. It is believed that Plate Tectonics is the reason for the movement of the continents hundreds of millions years ago from one huge landmass scientists called Pangaea into the positions where they are now.

If you use any of this information in your own work acknowledge this source in your bibliography like this:
Sydenham, S. & Thomas, R. Plate Tectonics [Online] www.kidcyber.com.au (2010)

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