Earth is the water planet, with 70% of the surface covered by water and accounting for 0.025% of the mass of the planet. The degree to which water is distributed and stored at depth, however, remains largely unconstrained. Yet water has a great influence on almost all of the physical and chemical properties of earth materials. This includes lower viscosity and seismic velocities, while enhancing electrical conductivity. Together with the observed viscosity increase in the lower mantle, observed mass flux from the upper to lower mantle, and lack of water storage capacity of the major minerals of the lower mantle, this suggests that the lower mantle is dry, leading to a transition zone water filter hypothesis at the base of the transition zone. Alternatively, the viscosity contrast between the upper and lower mantle can be explained without such a water filter by a change in the dominant mode of water storage between the upper and lower mantle. The hydrogen stored in the major minerals of the upper mantle is then stored in minor minerals of the lower mantle, leaving most of the volume of the lower mantle dry and stiff.
To test the central hypothesis of this proposal, this work will combine high-pressure and temperature experimental measurements using pioneering microfabricated samples for use in with theoretical computations. This will clarify the underlying physical and chemical processes responsible for variations in seismic wave speeds, viscosity, and electrical conductivity resulting from the presence of water at depth. The results of this work are broadly applicable to the field of Earth Science and beyond, with implications on the effects of glacial isostatic adjustment on present-day sea level rise to the design of solid-oxide fuel cells. Water-bearing rare-earth perovskites are potential solid-oxide fuel cell (SOFC) materials. A clear understanding of the mechanism of hydration of these materials, as well as the temperature stability limit of hydration can allow for a better design of these devices. Appreciation of the defect mechanisms active in deep-earth silicate perovskites will translate to these rare earth perovskites to allow for design of more efficient and more robust SOFCs. This CAREER award will also aid in development of several learning modules that integrate geophysical concepts and methods into courses taught across an earth science curriculum. In particular, these modules will have a focus on multivariant reasoning in scientific exploration. The effectiveness of these modules will be evaluated by pre- and post-testing of existing and to-be-developed ConcepTests. These modules will be created and tested in the PI's courses and later integrated into OSU's School of Earth Sciences courses.
