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Development of the plate tectonic theory

Why do the plates move?

Figure 5Earth's interior is subdivided in two different classifications (Fig. 5, right, click to zoom in):

Based on differences in composition:

Core: mostly iron
Mantle: mostly olivine
Crust: mostly silicate; solid, separated from mantle by Moho
oceanic crust: 5-6 km thick, basaltic, relatively dense continental: 20-70 km thick, granitic; lighter than basalt

Based on differences in rock behavior:

Inner core: solid
Outer core: molten (source of Earth's magnetic field) Inner mantle: mostly solid, but flows over millions of years
Asthenosphere: behaves like soft butter; part of mantle; present to about 350 km depth
Lithosphere: solid, cold; includes crust and outermost mantle; about 100 km thick;

Plates -- part of the lithosphere -- probably are carried along on top of the asthenosphere as the latter flows due to convection in the mantle. Convection, in turn, is driven by Earth's loss of heat. Thus:

heat loss->convection->plate motion->earthquakes & eruptions


updated January 28, 2002

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