Health & Science

In a rare diamond from Botswana, scientists found the existence of water deep inside Earth

A team of scientists analyzed a diamond from Botswana revealing that considerable quantities of water are stored deep inside Earth.

The diamond from Botswana whose composition proved large quantities of water exist in deep Earth
The diamond from Botswana whose composition proved large quantities of water exist in deep Earth | Goethe University Frankfurt

The research team, led by Tingting Gu from the Gemological Institute of America and Purdue University, in the scientific peer-reviewed scientific journal Nature published results that show water exists much deeper than previously believed.

The GIA analyzed a small and very rare diamond extracted in Botswana whose composition helped identify the presence of hydrous minerals.

This 1.5-centimeter diamond was formed at 660 kilometers (410 miles) below the surface and is part of the rare category of super-deep diamonds. The diamond came from the bottom of the Transition zone, a boundary layer that separates the Earth’s upper mantle and lower mantle. Plates hardly pass through beyond the transition zone from one mantle to the other. So there are plates that carry deep-sea sediments that can hold large quantities of water and carbon dioxide back in the Earth’s interior. However, they get stuck when they reach the transition zone.

The solidity of diamonds is the best time-capsule shell to protect minerals trapped inside deep earth for humans to see when they reach the surface. At this depth, temperature and pressure, up to 23 000 bars, are extremely high which modify the composition of minerals. Trapped inside diamonds, those minerals therefore tell the journey of rock, where it was formed and where it comes from.

The analysis of the diamond showed it contained a lot of water content that it came from a normal piece of the Earth’s mantle. As such, it demonstrates that the “transition zone is not a dry sponge, but holds considerable quantities of water,” explains Frank Brenker, professor at the Institute for Geosciences at Goethe University in Frankfurt. Hydrous conditions extend at least across the transition zone and into the lower mantle.

The transition zone could potentially store almost six times as much water as what is on Earth’s surface, but until now “we didn’t know whether it actually did so,” adds professor Brenker, member of the team who participated in the discovery.

They analyzed the diamond using a type of spectroscopy and X-ray diffraction, observing the stone  and its mineral imperfections without cutting it open, unlike for the discovery of Davemaoite, a compound observed for the first time after having opened a super-deep diamond from the lower mantle.

Water is therefore vastly present deep under Earth and the discovery helps explain how water circulates inner earth, the deep water cycle, until water eventually reaches to the surface through volcanic activity.

But the potential existence of a gigantic ocean does not look like how humans see water on the surface. An ocean in the transition zone is hydrous rock but it would not feel wet or drip water. Because the pressure is immensely different, elements as we know it change forms. Rock has various viscosity which helps explain the movement of tectonic plates, seismic and volcanic activity, for instance.

A previous diamond from Botswana studied in 2014 suggested similar results but it was too small to determine its precise chemical composition.

Read more about Botswana

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