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Roger Weller, geology instructor                         

Plate Tectonics
Erik Anderson
Physical Geology

Spring 2006

Plate Tectonics

The Earth’s surface is built on very large and rigid slabs of solid rock.  Plate tectonics is a theory that the Earth’s outer layer is broken into a dozen or more small and large plates that move in relation to one another on top of the mantle of the earth.  Many people believe that the continents of today were one all one super continent called Pangaea.  Then about 225-200 million years ago began to break up into what we live on today.




          Plate tectonics has helped to explain why earthquakes and volcanoes happen, and also why and how some of the biggest mountain ranges like the Himalayas and the Alps formed. 

            Another reason that people believe that there is continental drift is because of fossils found on different continents.  The same identical plant and animal fossils were found on the eastern coastline of South America, and the western coastline of Africa.  Still there is more evidence that the continents have been moving.  Their were signs of massive climate changes, like tropical plant fossils found in the form of coal deposits in Antarctica.  The only way for these plants to have been on this frozen landmass was that it must have been closer to the equator at some point in time.

            One of the ways that the plates are moving is form Sea-Floor Spreading.  Sea-Floor Spreading occurs in the Mid-Oceanic Ridges.  These ridges rise up from the ocean floor and are actually bigger than the Himalayan mountain range.  Making maps of the ocean floor has showed that these massive underwater mountain ranges have deep trenches in the center which runs the whole distance of the ridge.  In Some places these trenches can be more than 2000 meters deep.  Also the most heat comes from the centered peaks of the ridges. 







Diagrams of Mid-Oceanic Ridge thanks to UC Museum of Paleontology 

     The deepest waters in the ocean are found in trenches, some of which go as deep as 35,000ft below the earth’s surface.  Deep-sea trenches are usually associated with and run next to large continental mountain ranges.  They also are seismically active, but do not have the same high flows.  When the sea floor spreads it forces the thinner oceanic plates under the continental plates which are what creates a convergent plate boundary, and the deep ocean trenches.



            Everyone has theories to how or why the contents move or don’t move, or why there are fossils of the same species on to completely different continents.  There are even theories that the earth is actually expanding and that the whole earth was once completely covered by the continents.  But for me I believe the theory of Pangaea and that the plates are moving over the mantle of the earth.


Kious, W. Jacquelyne and Robert I. Tilling. “This Dynamic Earth: The Story of Plate Tectonics.” Eastern Publications Group 17 Feb. 2006: 13 Apr. 2006

Louie, J. “Plate Tectonics, The Cause of Earthquakes.” Nevada Seismological Laboratory 11 May 2001; 13 Apr. 2006

“Plate Tectonics: The Mechanism.” UC Museum of Paleontology 22 Sep. 1997, 13 Apr. 2006