Water—and Beyond—in Earth's Mantle

In the March 2012 issue of Physics Today, Marc Hirschman and David Kohlstedt explore the history of the deep water cycle, as well as the role of water in Earth’s mantle.

Earth cross-sectionCharacteristics of Earth’s deep water cycle such as the persistence of water on the planet’s surface and its storage in the planet’s interior are critical factors that affect plate tectonics. However, the influence is reciprocal with plate tectonics controlling the fluxes of water between near-surface and deep reservoirs.

In the March 2012 issue of Physics Today [1], Marc Hirschman and David Kohlstedt explore the history of the deep water cycle as it is linked to Earth’s history, as well as the role of water in Earth’s mantle from the microscopic considerations to the macroscopic consequences. The authors also note that carbon, like water, cycles through Earth’s interior with vast quantities being stored in the mantle and that it has an equally profound impact on Earth’s dynamics.

Earth’s early atmosphere and near-surface reservoirs were once rich in carbon, but the inventory of carbon in today’s mantle far exceeds that locked in crustal sediments and rocks. No one yet knows if the reversal came about early in Earth's history or developed over billions of years of plate tectonics. The authors speculate that the answer may lie in a deeper understanding of how carbon behaved during the magma ocean stage of Earth’s evolution.

The multiple links and relationships among the deep cycles of water, carbon, and other key volatiles clearly makes the study of all complementary.

Caption: The modern deep-Earth water cycle is strongly coupled to plate tectonics.

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