Plate Tectonics

Plate tectonics: The main features are:

• The Earth's surface is made up of a series of large plates (like pieces of a giant jigsaw puzzle).
• These 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.
• Convection currents beneath the plates move the plates in different directions.
  The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.

Where is the Evidence for Plate Tectonics?

The continents seem to fit together like a giant jigsaw puzzle:

If you look at a map, Africa seems to snuggle nicely into the east coast of South America and the Caribbean sea. In 1912 a German Scientist called Alfred Wegener proposed that these two continents were once joined together then somehow drifted apart. He proposed that all the continents were once stuck together as one big land mass called Pangea. He believed that Pangea was intact until about 200 million years ago

CONTINENTAL DRIFT

The idea that continents can drift about is called, not surprisingly, CONTINENTAL DRIFT.

When Wegener first put forward the idea in 1912 people thought he was nuts. His big problem was that he knew the continents had drifted but he couldn't explain how they drifted. The old (AND VERY WRONG!!) theory before this time was the "Contraction theory" which suggested that the planet was once a molten ball and in the process of cooling the surface cracked and folded up on itself. The big problem with this idea was that all mountain ranges should be approximately the same age, and this was known not to be true. Wegener's explanation was that as the continents moved, the leading edge of the continent would encounter resistance and thus compress and fold upwards forming mountains near the leading edges of the drifting continents. Wegener also suggested that India drifted northward into the Asia forming the Himalayas and of course Mount Everest.