Plate tectonics

The idea that the Earth’s continents are moving was first proposed by a German scientist, Alfred Wegener, in 1915. Wegener thought that around 300 million years ago there was a single continent, Pangaea (‘all land’ in Greek), which had divided into continents and drifted apart ever since.

People didn’t like Wegener’s ideas because he couldn’t explain the driving force behind the continents’ movements.  Another scientist called Arthur Holmes suggested that the movement could be due to the continual heating and cooling of the Earth’s mantle. Again, no one took much notice.

It wasn’t until the 1960s that scientists started to find evidence for Wegener and Holmes’s theories, when they started to better understand the ocean floor and worked out that:

  • The Earth’s surface is covered by crustal, or tectonic, plates.
  • The ocean floors are continually moving: spreading from the centre, sinking at the edges, and being regenerated.
  • The tectonic plates are moved by forces caused by convection currents beneath them.
  • The source of heat driving the convection currents is radioactivity deep in the Earth’s mantle.

The diagram below shows the boundaries of the tectonic plates and active faults.

The tectonic plates move in different directions by few centimetres each year (about the rate that your hair and nails grow), and this movement causes faults and earthquakes.