What does the Earth’s mantle hide? For a long time, scientists have debated about whether the depths of Earth are completely dry or contain water. Now, several discoveries have changed what we knew about this: there are huge amounts of water trapped inside the minerals in the Earth’s mantle, hundreds of km under the surface.
Even though we are not talking about liquid water like in the oceans, this water is part of the structure of certain rocks and this finding could transform our understanding about how the planet works. So, let’s find out more about this discovery.
A science-fiction mystery
Despite what we have learnt about Earth, many parts of our planets are still a mystery and one of the most intriguing ones is the mantle. This is the thick layer between the Earth crust and the core.
Writer Julio Verne imagined oceans hidden in the depths in his novel Journey to the Center of the Earth. Surprisingly, scientists discovered that that idea wasn’t far from reality: in the depths of the mantle could exist a kind of ‘’hidden ocean’’ inside the minerals.
Every beginning has a ‘’dirty’’ diamond
In 2009, a graduate student working with Dr. Graham Pearson, a geologist and geochemist from the University of Alberta, found a small, brown diamond that looked rather dull and dirty. When they analyzed it, they found something surprising: inside the diamond there was a strange mineral called ringwoodite, which can hold water inside its structure.
In this case, 1.5% of its weight was water, which is a lot if we think about the immensity of the mantle. It was the first real evidence of huge reservoirs of water deep inside the Earth.
A mineral formed in the depths
The ringwoodite can’t be formed on the surface, but on great depths where pressure and temperature are extremely high. This mineral can only exist between 410 and 660 km underground, in an area called ‘’transition zone’’ of the mantle.
Until now, this mineral was only found in meteorites like the one found in Australia in 1969. This is why the diamond discovered by Pearson’s team was the first example of the mineral coming from the inner Earth. The diamond that contained ringwoodite was brought up to the surface by a special kind of volcanic rock known as kimberlite, which forms deep within the mantle. Later, the diamond was found in a riverbed in Brazil and sold to researchers for just $20 — without anyone realizing how valuable it truly was.
A second diamond
In 2022, the mineral physicist Tingting Gu, from the Gemological Institute of America, found another important clue. She discovered a diamond from Botswana that contained not only ringwoodite but also two other minerals that can only form at depths of 410 miles or more. This discovery confirmed that water-containing minerals exist across a wide area of the mantle, not just in one small spot.
What this discovery about the mantle means
These findings suggest the mantle could contain more water than all the oceans of the surface together, water trapped inside the minerals. This ‘’inner ocean’’ could have a crucial role in how the planet works since scientists believe it influences in:
- Plate tectonics, the movement of the Earth’s crust that creates continents and earthquakes.
- Volcanic activity, by affecting how magma forms and rises to the surface.
- The planet’s heat and energy balance, helping to shape its internal processes.
So, thanks to a few tiny diamonds — one found in Brazil and another in Botswana — scientists now know that massive amounts of water exist deep inside the mantle, changing what we thought we knew about the inner workings of the Earth.