Earth has a ‘sixth ocean’. But you cannot see it

Earth has a sixth ocean, a new study suggests, but not where you can see. It’s hundreds of kilometres below the surface.

The international study published in Nature Geoscience says this vast reservoir of water is located in the so-called transition zone between the upper and lower mantle at a depth of 410 to 660 kms.

Researchers came to that conclusion by studying a rare Botswana diamond which, according to what its chemical composition suggested, was formed at a depth of 660kms in very watery conditions.

Natural diamonds are generally formed in the mantle at depths between 150 to 250 kms, but a few may come from much deeper down.

The water, though, does not splash around like on the surface of the earth but is locked up within the minerals there making this region very soggy.

“This also brings us one step closer to Jules Verne’s idea of an ocean inside the Earth,” ANI reports Prof. Frank Brenker from the Institute for Geosciences at Goethe University in Frankfurt as saying.

Except that there is no water seen or even felt in this ‘ocean’. It’s just present in the hydrous mineral ringwodite present there throughout the transition zone.

How did scientists find out all that from looking at that diamond? Simple. The Botswana diamond has “inclusions”, or pockets, of ringwodite – a flaw that would make it less valuable at the jewellers, but priceless in a lab.

The study confirmed something that for a long time was only a theory, namely that ocean water accompanies subducting slabs and thus enters the transition zone. This means that our planet’s water cycle includes the Earth’s interior.

So, how much water would be there in the transition zone? Theoretically, the transition zone would be able to absorb six times the amount of water in our oceans.

“So we knew that the boundary layer has an enormous capacity for storing water,” Brenker says. “However, we didn’t know whether it actually did so.”

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