Mantle transition-zone water filter

Article By:

Bercovici, David Yale University, New Haven, Connecticut.

Karato, Shun-ichiro Yale University, New Haven, Connecticut.

Last reviewed:2005

DOI:https://doi.org/10.1036/1097-8542.YB051110

The Earth's mantle is the 2900-km-thick (1800-mi) layer of rock between the crust and the iron core. Although solid, the mantle flows very slowly through solid-state creep (similarly to how glaciers flow), moving about as fast as human fingernails grow. What makes the mantle move is convection, the process of hot buoyant material rising and cold heavy material falling. Convection in the mantle is powered by both heat production from decay of radioactive isotopes (such as uranium and thorium) and the loss of primordial heat left over from the Earth's accretion (that is, impact-generated heat). Mantle convection drives plate tectonics (continental drift) and all its attendant phenomena such as earthquakes and volcanoes. Over geologic time scales, mantle convection is vigorous and should thoroughly stir the mantle. However, considerable evidence exists to suggest that the mantle is poorly mixed, and even layered. This paradox of the well-stirred but unmixed mantle remains one of the unsolved mysteries of the Earth's interior and has been an area of active debate for decades. Its solution is at the heart of understanding the nature and structure of mantle convection, the history of cooling of the entire globe, and the chemical differentiation of the Earth (for example, formation of continental crust and oceans from the mantle).

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