b'Carnegie Science|Spring/Summer 2020 7A Deep-Earth Water Cycle?Earths water cycleevaporation, condensation, precipitation, and collectionis obvious at the surface. But it may be possible that there is a deep-Earth component of this process making our planet ideal for sustaining life.New work published in the Proceedings of the National Academy of Sciences Lead author Yanhao Lin is a Carnegie postdoctoral associate (left). He arrived from by Carnegies Yanhao Lin and Michael Walter, along with former Carnegie scientists and ongoing collaboratorsVrije Universiteit Amsterdam. He conducted the work with Mike Walter (right) and team. Ho-Kwang Dave Mao and Qingyang Hu of the Center for HighImages courtesy Carnegie Institution for SciencePressure Science and Technology Advanced Research Shanghai and Yue Meng of Argonne National Laboratory, demonstratesStishovite is a silica-based mineral and a major component of that a key mineral called stishovite is capable of storing andthe oceanic crust, explained Mao. In plate tectonics, there are areas transporting large amounts of water under extreme conditionscalled subduction zones where an oceanic plate slides beneath a like those found in Earths lower mantle. continental plate, sinking from the Earths surface into its depths. The result shows that substantial quantities of water couldWhen this happens, stishovite is transported into the mantle.be present deeper in the mantle than previously thought,The discovery of diamonds with water-containing mineral indicating that a whole-mantle water cycle is possible. inclusions that come from depths to about 435 miles down (700 To get down into the mantle, water must be incorporatedkilometers) in the mantle revealed that water does get at least that into minerals on the surface and then be stably maintained infar if it finds the right mineral partner.those structures under the conditions found deep inside theTo investigate whether stishovite is such a partner for lower planet, explained lead author Lin. depths, the team subjected tiny samples of stishovite with water to The researchers used lab-based mimicry to study thea range of about 320,000 to 510,000 times normal atmospheric mineral stishovite, which is a high-pressure form of quartz, whenpressure and heated it to a range of about 1800F to 2730F (1000C partnered with water under high-pressure and temperatureto 1500C), simulating a transition from upper mantle conditions to conditions. Its known that substantial amounts of water can belower mantle conditions. Remarkably, they found that stishovite stored in silicate minerals in the Earths upper mantle, betweencan accommodate large amounts of water under these conditions.about 60 to 415 miles deep (100 and 670 kilometers). But the teamIf water can be stored in minerals at lower mantle pressures examined stishovite and water under simulated conditionsand temperatures, it could indicate that there is a global water cycle found deep in the lower mantle, between about 415 to 1800 milesoccurring on very long geologic timescales, explained Walter. This down (670 and 2900 kilometers), where it was believed that muchcould alter our understanding of how deep planetary interiors may less water could be stably stored in minerals. influence or control the water content at the surface.Arc VolcanoHOT SPOTRe gasket Unheated area Silver paint SLAB PLUME MORUPPER MANTLEIron oxide St LOWER MANTLEStCORERe gasketThe Earths interior is dynamic This microphotograph shows a tinywith materials flowing to andSUPPORT:sample of the mineral stishovite.from the surface. This cutawayThe U.S. National Science Image courtesy Yanhao Lin shows the layers of the interior.Foundation supported this Image courtesy Yingwei Fey,work, in part.Carnegie Institution for Science'