Distinguish between relative and absolute dating

There are three major types of rock: igneous, sedimentary, and metamorphic.The rock cycle illustrates the relationships among them (see diagram).

The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.

The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America.

The remnants of this plate on the surface of the Earth are the Juan de Fuca Plate and Explorer Plate, both in the northwestern United States and southwestern Canada, and the Cocos Plate on the west coast of Mexico.

There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle (that is, the heat transfer caused by bulk movement of molecules within fluids).

Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction — because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convecting mantle.

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