Water under the earth’s crust! But how did it get there?

Pamela Henriquez weathered chili 6 minutes
Earth
The Earth’s layers extend from the core to the Earth’s surface. Three general groups are distinguished according to their composition: the geosphere, the hydrosphere and the atmosphere. Each layer builds up a higher temperature as it gets closer to the core, due to increased pressure.

When we refer to the interior of the Earth, we realize that we know very little about what happens there. But new technologies have made it possible to know more about certain areas describing its composition and dynamics.

Despite this, some doubts remain. especially about the presence of water under the earth’s crust. Some stories say yes. In Jules Verne’s fictional 1864 book Journey to the Center of the Earth, for example, There was already talk of inland oceans, but it was not until 2014 that the first scientific study showed evidence of the presence of water at a depth of 500 km.

The study by experts from the United States, Italy and Germany, published in an article in the journal Nature Geoscience, provides new evidence for the existence of significant amounts of water between the upper and lower mantle of the Earth – at about 410 and 660 km depth.

“The study confirms something that has long been just a theory, namely that ocean water accompanies subduction losses and thus enters the transition zone.

“This means that our planet’s water cycle includes the interior of the Earth,” explains the Institute of Geosciences of the Goethe University of Frankfurt, to which three of the study participants belong.

Low pressure in the deep

Between the upper mantle and the lower mantle of the Earth is the so-called transition zone (TZ). The pressure can reach 23 million millibars, resulting in a change in the crystalline structure of the olive-green mineral, which makes up about 70% of the Earth’s upper mantle.

At the upper limit of the TZ, at a depth of 410 kilometers, it becomes a denser mineral, wadsleyite, and at 520 kilometers it becomes another mineral, ringwoodite, even denser than the first. “Mineral transformations make it very difficult for rocks to move through the mantle,” explains Professor Frank Brenker of the Institute of Geosciences.

Until now, the long-term effects of the suction of materials in the transition zone on its geochemical composition and whether there were higher amounts of water were unknown. Professor Brenker thinks that subduction losses also transport deep-sea sediments into the Earth’s interior.

“These sediments can contain large amounts of water and CO2, but until now it was not known exactly how much water enters the transition zone in the form of hydrated minerals and more stable carbonates, and therefore it was also not known whether large amounts of water were actually stored there.”

Analysis of a found diamond

The authors analyze a diamond from Botswana that formed at a depth of 660 kilometers, between the transition zone and the lower mantle, where ringwoodite is the predominant mineral.

Analysis revealed that the stone contains numerous ringwoodite inclusions, which exhibit a high water content. In addition, the chemical composition of the stone could be determined.

Jules Verne’s idea of ​​an ocean inside the Earth is far from reality. There would be no real ocean in the depths, but rather an area of ​​hydrated rock.

Brenker comments: “In this study, we have shown that the transition zone is not a dry sponge, but contains considerable amounts of water. It also brings us closer to Jules Verne’s idea of ​​an ocean inside the Earth. The difference is that there is actually no ocean in the depths, but hydrated rock”, explains Professor Brenker.

Diamond
Diamond with inclusions or internal water formations. Images from Nature Geoscience.

Hydrated ringwoodite was first detected in a transition zone diamond in 2014; Brenker was also involved in this study. Nevertheless, it was not possible to determine the precise chemical composition of the stone because it was too small.

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