A recent study has revealed the presence of a massive ocean deep in the Earth’s rocky mantle. This discovery should help scientists to understand the Earth’s water cycle and how tectonic plates move the oceans between our planet’s surface and “inner reservoirs.”

(The Earth’s mantle is the layer of hot rock found between the Earth’s core and the crust.)

Scientists have long assumed that the transition zone of the Earth’s mantle (which lies between the upper and lower parts of the mantle, between 410 and 660 kilometers below the Earth’s surface) may contain water, held by a rather rare type of rock. If direct evidence of the existence of this aquatic zone has long been lacking for scientists, it is now well available.

Earth's Mantle

Earth’s Mantle

To be able to affirm that this transition zone was indeed a reservoir of water hidden in the depths of the Earth, the researchers carried out experiments on water-rich minerals after analyzing the seismic waves that cross the Earth’s mantle under American territory. They then discovered that material transiting to the lower part of the Earth’s mantle entered into fusion as it moved away from its transition zone.

“If we could observe this phenomenon, then the presence of water in this transition zone is inevitable,” said Brandon Schmandt, seismologist at the University of New Mexico and co-author of the study published in the journal “Science.”

Laboratory studies have shown that these minerals can contain water in forms other than liquid, solid, or gas: water is “trapped” in the molecular structure of Ringwoodite. Ringwoodite is an extremely rare type of mineral derived from olivine, which forms only under very high pressures and temperatures, precisely those present in the transition zone of the Earth’s mantle.

According to Graham Pearson, a mantle specialist at the University of Alberta (who was not involved in this work), “this study is an important tool for understanding the role of this transition zone on hydrogen fluxes deep in the Earth.”

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