KEY POINTS IN THIS CHAPTER •
Plate tectonics was proposed by Alfred Wegener, a meteorologist who was the first to notice the similarities between the western edge of Africa and the eastern edge of South America.
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The plates represent crustal areas that migrate or float on magma. Convection currents cause the magma to rise and fall in various places.
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A major plate is greater than 40 million square kilometers in area. The largest plate is the Pacific. There are numerous minor and micro plates.
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Plates come together or separate. These are called convergent and divergent boundaries, respectively.
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Convergence can happen with or without subduction or sinking of half of the boundary beneath another. The sinking half is denser and is often the oceanic half if ocean and continental regions are coming together.
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Convergence without subduction usually creates giant mountain ranges in the middle of a continent.
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Divergence can happen in oceanic situations or on land. In both areas of the world, it gives rise to rift valleys where magma comes up from beneath thinner crust.
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In transform boundaries, plate edges are slipping past each other. Here is where you will get a great many earthquakes as the shift is dextral or sinistral in nature.
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