Last week a study, published in the scientific journal Nature, provided the first direct evidence that parts of deep Earth are hydrous, with possibly as much water trapped in Earth’s transition zone as there is in all the world’s oceans.

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For the last few decades, scientists have been trying to understand whether the deep Earth is dry, wet, or wet in patches. Prior to the new findings, ringwoodite, a mineral that contains water within its structure, had only been found in meteorites. However, the presence of the mineral within a diamond from the Earth’s mantle provides the first terrestrial evidence confirming that water is present within the deep Earth.

The research was conducted on a diamond from a 100-million-year old kimberlite rock from central-west Brazil that was brought to the surface through volcanic eruptions. It was found to contain the mineral ringwoodite, which is thought to only form in the transition zone, which is between 410 km and 660 km beneath the Earth’s surface.

The results revealed that the diamond has a water content of approximately 1.0%. Although this value may appear insignificant, ringwoodite makes up an extremely large proportion of the deep earth, with this acting as a major repository for water that may contain an ocean’s equivalent, or more, of water.

Looking beyond Earth, ringwoodite is also expected to form deep within other planets, suggesting that water may be stored in the mantle of rocky planets, including Mars. Further research will aim to predict the amount of water trapped within the interior of other planets in our galaxy, as well as understand exactly how Earth’s plate tectonics control the processes by which water is recycled deep within the mantle.