Water in the Mantle; A Scoping Proposal

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The habitability of Earth depends fundamentally on the sustainable presence of liquid water at its surface, but water plays a far greater role in creating a platform for life than simply providing the medium for life and climate at the surface. Small variations in the water content of the mantle changes the minerals properties and specifically their viscosity in the mantle (Mei and Kohlstedt JGR 105, 21457-21469, 2000) with fundamental repercussions on the mode and efficiency of mantle convection (McGovern and Schubert EPSL 96, 27-37, 1989) and may even determine the distribution of incompatible elements in the mantle and their availability to surface systems (Bercovici and Karato Nature 4125, 39-44, 2003). Convection in turn, as well as being the principle mechanism for planetary cooling, controls ocean crust production; continental breakup; plate movement and mountain creation; and flux of water and other volatiles into and out of the mantle. It is clear that mantle convection determines and possibly regulates the habitability of our planet, yet our basic understanding of fundamental controls of this system by the deep Earth, and specifically the critical role of wate over geological time, is woeful.