A groundbreaking studypublished in Nature reveals compelling evidence of a vast ocean trapped deep within the Earth’s mantle, about 400 miles beneath the surface.
This hidden water reservoir, stored within a rare mineral called ringwoodite, challenges previous ideas about how much water the planet holds. Scientists now believe that Earth’s interior contains as much water as all the surface oceans combined, locked inside mantle minerals under extreme pressure and heat.
Ringwoodite and the Deep Earth Water Cycle
The discovery focuses on ringwoodite, a high-pressure mineral that forms in the Earth’s mantle between 250 and 410 miles deep. What makes ringwoodite unique is its ability to store water molecules within its crystal structure. Steve Jacobsen, a co-author of the study, explained, “Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight.” He continued, “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.” This finding suggests a continuous water cycle not just on the surface but through the entire Earth.
Evidence of Deep Melting Linked to Water ReleaseBrandon Schmandt, another co-author, pointed out the unusual melting of mantle rock at such great depths: “Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles.” He added, “If there is a substantial amount of H2O in the transition zone, then some melting should take place in areas where there is flow into the lower mantle, and that is consistent with what we found.” This melting is driven by the release of water from ringwoodite as it changes form under intense pressure. Jacobsen noted, “Whether or not this unique sample is representative of the Earth’s interior composition is not known, however. Now we have found evidence for extensive melting beneath North America at the same depths corresponding to the dehydration of ringwoodite, which is exactly what has been happening in my experiments.”
Unique Properties of Ringwoodite and Its Water Storage CapacityRingwoodite’s ability to hold water is extraordinary. Jacobsen remarked, “There is something very special about the crystal structure of ringwoodite that allows it to attract hydrogen and trap water. This mineral can contain a lot of water under conditions of the deep mantle.” Laboratory experiments simulating mantle conditions showed that ringwoodite can hold over one percent of its weight in water, bound as hydroxyl radicals inside its crystal matrix. This trapped water reservoir influences many geological processes by affecting the physical and chemical behavior of mantle rock.
Seismic Confirmation of Mantle Melting and Subduction ProcessesUsing seismic data from the USArray network across North America, scientists gained clearer insight into the Earth’s internal structure. Schmandt explained, “Seismic data from the USArray are giving us a clearer picture than ever before of the Earth’s internal structure beneath North America. The melting we see appears to be driven by subduction — the downwelling of mantle material from the surface.” This subduction-related melting matches the water release from ringwoodite, supporting the idea that water affects deep mantle convection and tectonic movements.
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