Tuesday, August 07, 2012
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Quote:
Originally Posted by uzma riaz
Rules for plate movement...
1.continental crust is less dense than oceanic crust so it does'nt sink.it is never destroyes and is permanent.
2.oceanic crust is heavier so it can sink below continental crust,it is constantly being formed and detroyed at ocean ridges and trenches.
3.continental crust can carry on beyond the edges of the land and finally end far below the sea.This explains why the edge of all the continents dont have deep trenches right up against their coastline.
4.Plates can never overlap. This means that they must either collide and both be pushed upto form mountains, or one of the plate must be pushed down into the mantle and be detroyed.
5.There can never be gaps between plates,so if two plates move apart as in the middle of the atlantic,new rock will be formed to fill the space.
6.The earth is not getting bigger or smaller,so the amount of new crust being formed must be the same as the amount being destroyed.
7.Plate movement is very slow.This is partly why Wegner's ideas were ignored.Nobody could see the continents moving.When the plates make a sudden movement we call it an earthquake and its the only time when we are directly aware of the plates movement.
hope this answer will satisfy your question about rules.
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http://www.geography-site.co.uk/page...arth/tect.html
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