Plate Tectonics

Plate tectonic theory was proposed in the 1960's, and is our current best explanation for the movement and behaviour of the Earth's outermost layer.

The surface of the Earth is made up of 12 major plates and a number of minor ones, ranging from 80 to 120 km thick, and incorporate both oceanic and continental crust. All are in constant motion, moving in different directions at about 1 - 10 centimeters per year, which over millions of years translates into a long way!

The movement of these plates causes earthquakes and volcanos which reshape the continents and ocean floor.

The tectonic plates are made up of the Earth's crust and part of the upper mantle, known as the lithosphere. The lithosphere is broken into giant plates. These plates are about 80 - 120 kilometers thick, and fit around the globe like a giant puzzle, moving abit each year.

These plates sit on the asthenosphere - a hot (1600 C) layer and is more 'plastic' like silly putty, as the minerals are almost at their melting points. The flowing asthenosphere carries the lithosphere of the Earth.

Why do the plates move? It is not fully understood, but most scientists believe that convection currents - which occur when temperatures at the bottom are hotter than at the top - like in a boiling pot of water. These convection currents carry along the plates like a conveyor belt.

Click here for more on the evidence for plate tectonics.

250 million years ago, there was a single gigantic continent called Pangea.

The breakup of Pangea. The continents are still in motion today, causing earthquakes, volcanic eruptions, and tsunamis.

(Graphics used with permission from Woods Hole Oceanographic Institute and courtesy of Windows to the Universe.)

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