The assumption that the earth’s continents are fixed in one place was challenged in the early twentieth century by German earth scientist Alfred Wegener. He proposed that all the contentents existed as one body of mass, called a “supercontinent”. Unfortunaty his proposal was rejected during his time because there was no explanation for why the continents moved.

However, in the 1960’s researchers came out with the plate tectonics theory to explain Wegener’s idea. This theory states the reason for continental movement, is due to the free flowing liquids underneath it called the mantle. The current

of liquid travels along the convection current. The movement of the tectonic plates is the cause for earthquakes, volcanic eruptions, and the creation of mountains. The plate tectonic theory not only explains the movement of the continents but can explain mid-ocean ridges, and deep sea trenches. In the ocean, where crustalplates collide the crust is forced downwards.

Figure A

Additionally, shapes of the continents suggest their once wholeness as “Pangea”. In addition to the “jig saw” fit of continents, similar fossil similarities. For example the Mesosaur was found in both south america and south africa.

Figure B

In addition Harry Hess, a geologist at Princeton proposed that the mid-ocean ridges marked regions where hot magma rose close to the surface. His theory was proven when the U.S Navy published a summary on sea floor magnetism. The found magnetism bands of alternating strong and weak magnetism in the rocks of the seafloor.

Figure C

This clip mentions additional evidence of plate tectonics including some of the points already presented.

References:

Figure A: was an image from http://io.uwinnipeg.ca/~simmons/16cm05/1116/16evolut.htm

Figure B and C: are both from http://www.visionlearning.com/library/module_viewer.php?mid=65

The video can be found at http://www.youtube.com/watch?v=gCehZwV6fcA&feature=related

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