PLATE TECTONICS AND EARTH'S STRUCTURE

(CS-6.science1a)

Schematic map of the earth's major plates

What do the words 'Plate Tectonics'  mean?  Plates, as you know, are large flat pieces.  Tectonics is the study of the earth's structural features. So plate tectonics means the study of the earth's plate structure.  The basic idea is that millions of years ago the surface of the earth did not look as it now looks.  The pieces (plates) were closer together and over many years drifted apart.  'Drifted' sounds like the plates are floating on something and indeed they are.  The plates, which are solid, are floating on the liquid mantle of the earth.  It looks something like this:

The theory is called 'Continental Drift'.  The picture below is an animation showing the continents drifting apart on the earth's surface. The time scale is from 800 million years ago to the present.  The configuration of continents that we now see moved into place about 50 million years ago. 
 

The evidence that the plates are there and moving includes the following:

• The location of earthquakes, volcanoes and mid ocean ridges.
• The distibution of fossils, rocktypes and climatic zones
  
  

Visit this website which discusses the evidence for plate tectonics.   When you have finished looking at the evidence, click the blue text to have a look at the different layers of the earth.