Tech UPTechnologyThe Earth has an 'ocean' 660 km deep

The Earth has an 'ocean' 660 km deep

 

A pinch of ocean inside the planet? It is not literally an underground “ocean”, but it is a huge amount of water trapped inside minerals, as they have been able to discover in a new investigation published in the journal Nature Geoscience.

 

Water can penetrate deeper than previously thought

The key has been given by a rare diamond (type IaB) found in the mines of Botswana (Africa), which has provided more details about the region between the upper and lower mantle of the Earth, known as the transition zone or discontinuity of 660 km. This class of diamonds forms deep underground and usually stays in the Earth for a long time.

The conclusion of this study is that it is a region very rich in water. Finding large amounts of water underground on a planet whose surface is 71% water may not seem like a great find; however, yes it is. The liquid water in all of Earth’s oceans is just a puddle compared to the water content below the Earth’s crust.

As it is, there is also water in minerals more than 200 miles below ground, including in the upper mantle, the semi-malleable layer on which the crust “floats.” The researchers found that the diamond contained inclusions, or small fragments of other minerals, which may contain more water and appear to have existed at the boundary between the upper and lower mantle. The results suggest that there may be a lot of water deeper than previously thought, which would have other implications, for example for plate tectonics. The goal is for scientists to be able to incorporate the findings of this study into models of how water in the mantle might influence processes such as Earth’s internal convection current .

“These mineral transformations greatly hinder the movements of the rocks in the mantle,” explains Frank Brenker of the Institute for Geosciences at Goethe University Frankfurt. “For example, mantle plumes, rising columns of hot rock from the deep mantle, sometimes stop directly below the transition zone. Mass motion in the opposite direction also stops. Subducting plates often have a hard time to traverse the entire transition zone. So there is a whole graveyard of such plates in this zone under Europa .”

Until now, the long-term effects of the “suction” of material in the transition zone on its geochemical composition and whether larger amounts of water existed there were unknown. The water seems to slip deeper into the planet and reaches the lower mantle.

 

Analysis

The dense minerals wadsleyite and ringwoodite can (unlike olivine at shallower depths) store large amounts of water, in fact so large that the transition zone could theoretically absorb six times the amount of water in our oceans, experts say.

The researchers used micro-Raman spectroscopy and X-ray diffraction to probe the 12 mineral inclusions and a group of milky inclusions found in diamond. They found a mixture of minerals in these inclusions ranging from ringwoodite (magnesium silicate) to ferropericlase (magnesium/iron oxide) , as well as enstatite (a form of magnesium silicate). In addition, the research group was able to determine the chemical composition of the stone. It was almost exactly the same as virtually all mantle rock fragments found in basalts anywhere in the world.

Its content suggests that the diamond formed in the transition zone, 660 km below the Earth’s surface.

“In this study we have shown that the transition zone is not a dry sponge, but contains considerable amounts of water. This also brings us one step closer to Jules Verne’s idea of an ocean inside the Earth,” concludes Brenker. The only difference is that instead of an ocean there are hydrated rocks.

Reference: Tingting Gu, Martha G. Pamato, David Novella, Matthew Alvaro, John Fournelle, Frank E. Brenker, Wuyi Wang, Fabrizio Nestola. Hydrous peridotitic fragments of Earth’s mantle 660 km discontinuity sampled by a diamond. Nature Geoscience, 2022; DOI: 10.1038/s41561-022-01024-y

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