Continental Drift

The Earth's Surface 

 

It is thought that the crust, underneath the oceans as well as the continents, together with the upper part of the mantle is divided into huge 'rafts' called plates.  The movement of the plates will be explained below, by the theory of continental drifts.

 

Amongst these plates there are 8 major ones and assortment of smaller ones.  The major plates include the following:

1. The African plate
2. The Antarctic plate
3. The Indoaustralian plate
4. The Eurasian plate
5. The Nazca plate
6. The North American plate
7. The Pacific plate
8. The South American plate

The diagram below indicates the different plates on the world map which shows that the plates are capped by both the oceanic and continental crust.  Most volcanoes are found around and along the plate edges.

 

 

Continental Drift - Plate Tectonics

During 1915, German scientist Alfred Wegener put forward this idea of continental drift.  He proposed that today's continents once formed a single landmass, which he named Pangaea (Greek for 'all land').  This 'snapped' into pieces due to the weaknesses in the earth's crust as they were made up of less dense materials.  These 'huge chunks' of land drifted centimeter by centimeter over millions of years until they got to where they are now.  See animation below.

 

Jigsaw Fit

 

Continental Drift

 

So, what evidence is there to prove the existence of the Pangaea?

 

If you look at the present day map of the world, there is an obvious jigsaw fit between Africa and South America.  The other continents can also be fitted in without too much difficulty (see animation above).   The distribution of some fossil plants and animals provides further evidence to support the theory of continental drift.  Matching plant fossils of the same era have been found in rocks in  South America, South Africa, Australia, Antarctica, and India, which strongly suggests that they were all joined once upon a time.  Identical fossils of a freshwater crocodile, Mesosaurus, fold mountain chains and glacial deposits found in both Brazil and South Africa also back the theory.  

 

The symmetrical pattern of 'magnetic stripes' found in the rocks on either side of the Mid-Atlantic ridge is the clearest evidence found only recently that indicate the two sides are spreading away from each other (see animation above).

 

Mid-Atlantic Ridge

Continue... Plate Boundaries