The purpose of this projects is to provide a new set of laboratory data to understand the deep mantle water cycling. Possible melting near the 410-km and its consequence on geochemical cycling have been speculated. However, there have been no definitive studies on the conditions for partial melting under the deep upper mantle conditions. Consequently there have been large uncertainties on the critical water content. In this proposal, our efforts are focused on determining the critical water content for partial melting near 410-km depth. The critical water content for partial melting is a critical parameter to understand the deep water cycling including the origin and evolution of the ocean mass and the processes to control the water content in the upper mantle. In this project, we will use electrical conductivity to determine the onset of partial melting and consequently, the results of this work will also provide a critical new. . . The complete abstract for this award is available in Research.gov at: www.research.gov.