A water body, nicknamed as the Earth’s sixth ocean, that is three times the volume of all the five oceans, exists underground, an international study has found. The reservoir is located between the transition zone (TZ) of the Earth's upper and lower mantle. This means that our planet's water cycle includes the Earth's interior. The research team analysed a rate diamond formed 660 meters below the Earth's surface using techniques including Raman spectroscopy and FTIR spectrometry.
What has the study found?
Evidence of the sixth ocean was discovered while analysing a rare diamond that had taken form 660 km inside the Earth. This has confirmed a long-time theory that ocean water accompanies subducting slabs, and thus enters the transition zone. Subduction is a geological process in which the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the denser plate dives under the second plate and sinks into the mantle.
"These mineral transformations greatly hinder the movements of rock in the mantle," explains Prof. Frank Brenker from the Institute for Geosciences at Goethe University in Frankfurt. "The subducting slabs also carry deep-sea sediments piggyback into the Earth's interior. These sediments can hold large quantities of water and CO2. Until now, it was unclear just how much enters the transition zone in the form of more stable, hydrous minerals and carbonates, and whether large quantities of water are really stored there."
What have scientists found about the diamond?
The diamond was formed at the interface between the TZ and the lower mantle at a depth of 660 km, where the dominant mineral is ringwoodite. Research shows the stone contains ringwoodite inclusions that exhibit high water content. The chemical composition of the stone has been determined, which is nearly identical to the fragments of mantle rocks found in basalt. This indicates the diamond comes from a piece of the Earth’s mantle. “In this study, we demonstrate that the transition zone is not a dry sponge, but holds considerable quantities of water. This also brings us one step closer to Jules Verne's idea of an ocean inside the Earth,” says Brenker.
What was Jules Verne’s analysis?
In 1869, French writer Jules Verne wrote a classic science fiction adventure novel titled Twenty Thousand Leagues Under the Seas. It implies the distance travelled under the various seas: 20,000 metric leagues (80,000 km, over 40,000 nautical miles), almost two times the Earth’s circumference.