The surface of the lithosphere is fractured into a number of tectonic plates (also known as lithospheric or crustal plates) which are in constant motion. As these plates move and collide, the lithosphere buckles, warps, and is torn apart. When this occurs, the Earth's surface shakes with great force, like that which accompanies earthquakes. Volcanoes are common along many plate boundaries as well.
Figure 15.1 Major Tectonic plates of the world
Plate tectonics refers to the process of plate formation, movement, and destruction. It finds its foundations in two theories, continental drift and sea-floor spreading. Continental drift describes the movements of continents over the Earth's surface. Sea-floor spreading refers to the creation new oceanic plate material and movement away from the midocean ridge. It was Alfred Wegener in the early 1900's who brought forth the concept that the "shell" of the Earth's surface was fractured, and these "pieces" drifted about. Blasphemy in the minds of scientists of Wegener's day, some 50 years later his ideas were finally accepted. Wegener was able to piece together (pardon the pun) several bits of information which led to his conclusion that the present configuration of the continents is not the same as it was in the past. In fact, the continents were one "super-continent" called Pangea.
Figure 15.2 The supercontinent of Pangea
Look at a map of the Earth like that in Figure 15.3. Carefully examine the east coast of South America and then let your eyes drift to the west coast of Africa. It looks like you could "fit" South America up against Africa like a puzzle. The same can be said for the fit between North America, Africa, and Europe (Figure 15.4)
Figure 15.3 Present location of world
Figure 15.4 Fit of continental land masses
When we slide the continents together, some over lap between the land masses occurs. This is possibly due to the creation of exotic terrain, new land that has been formed somewhere else and moved to its present location. This remarkable correspondence provides circumstantial evidence for the theory of continental drift. Watch "Exotic Terrane" then return here.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.