A water-bearing crystal of ringwoodite was reported inside a diamond in 2014, offering direct evidence that water can be stored in minerals deep in Earth’s mantle. The “ocean” in the headline is a metaphor: the finding was not an underground sea, and it did not measure how much water the mantle contains.
What was found inside the diamond?
The 2014 report described a tiny inclusion of ringwoodite—a mineral that can contain water—encased in a diamond. Chemistry World presented the inclusion as direct evidence supporting the idea that water is stored in minerals in the mantle transition zone. Chemistry World’s March 2014 report and the Royal Society of Chemistry’s later education-page version both describe the discovery.
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Why does the report call it an “ocean”?
Here, “ocean” means water held within deep-Earth minerals, not a cavern or continuous pool of liquid water. Ringwoodite can incorporate water into its mineral structure under the relevant deep-Earth conditions, so the finding concerns water carried in rock rather than a hidden body of seawater.
How deep is the water-bearing region?
The coverage places the mantle transition zone at roughly 500 km below Earth’s surface. That is an approximate depth for the region associated with the inclusion, not a claim that the diamond or crystal marks a single precise boundary or an entire reservoir at that depth.
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Does the mantle contain more water than all the oceans?
The reports say the broad deep-Earth reservoir could contain more water than all the world’s oceans combined. That is an inference about a large region based on evidence such as the small inclusion; it is not a measured global inventory. The coverage does not provide a quantified total for the mantle’s water content.
What the discovery does—and does not—show
- Observed: a water-bearing ringwoodite inclusion was reported inside a diamond.
- Supported: water can be stored in minerals in the mantle transition zone.
- Not established by this find alone: the total amount of water held throughout the mantle, or a direct comparison of measured mantle and ocean inventories.
The 2014 coverage does not supply enough detail to reconstruct analytical methods, sample provenance, uncertainty ranges, or a measured global total. The distinction matters: a tiny sample can support the presence of water in deep minerals without directly measuring the scale of the full reservoir.
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