There are five oceans on Earth: the Atlantic, Pacific, Indian, Arctic, and Southern Ocean. An international team of scientists has now found evidence of considerable quantities of water between the Earth’s upper and lower mantle.The evidence was found during the analysis of a rare diamond that formed 660 kilometers below the Earth’s surface confirming the theory that ocean water accompanies subducting slabs and thus enters the transition zone. The new findings reveal that Earth’s water cycle includes the Earth’s interior.
The evidence points to water in the transition zone (TZ), the boundary layer that separates the Earth’s upper mantle and the lower mantle. The boundary is located at a depth of 410 to 660 kilometers, where immense pressure of up to 23,000 bar causes the olive-green mineral olivine to alter its crystalline structure.
Olivine constitutes around 70 percent of the Earth’s upper mantle and is also called peridot. Researchers said that at the upper boundary of the transition zone, at a depth of about 410 kilometers, it is converted into denser wadsleyite; at 520 kilometers it then metamorphoses into even denser ringwoodite.
“These mineral transformations greatly hinder the movements of rock in the mantle. Subducting plates often have difficulty breaking through the entire transition zone. So, there is a whole graveyard of such plates in this zone underneath Europe,” explains Prof. Frank Brenker from the Institute for Geosciences at Goethe University.
The team explains that the transition zone’s high-water content has far-reaching consequences for the dynamic situation inside the Earth and if it is to be breached, it could lead to a mass movement in the crust.