Archive · 15 Sep 2026
Earth’s Deep Mantle May Store Two Pacific Oceans’ Water
Scientists think a huge amount of Earth’s water may be hidden deep inside the planet.
It could equal the water in about two Pacific Oceans.
The water would not form a giant underground sea.
Instead, it would be stored inside special minerals.
Researchers made two possible minerals in a laboratory using very high heat and pressure.
These conditions may be similar to those near Earth’s core.
The minerals could have formed when early Earth’s molten interior cooled.
However, scientists have not yet proved that these minerals exist inside Earth today.
The discovery may help explain how Earth kept its water over time.
A study suggests water equivalent to two Pacific Oceans could be stored about 2,900 kilometres beneath Earth’s surface.
Researchers identified two previously unknown iron oxyhydroxides, Fe5O12Hx and Fe7O12Hx, that can retain substantial water.
The minerals were produced in laboratory experiments using extreme pressures and temperatures created with diamond tips and lasers.
The proposed water would be chemically held inside minerals near the mantle–outer-core boundary, not present as underground oceans.
Scientists caution that there is no direct evidence these mineral phases currently exist inside Earth.
- Who
- Researchers studying Earth’s deep interior, with commentary from geoscientist Alfred Wilson of the University of Leeds.
- What
- A study identified two iron oxyhydroxides that could store water deep within Earth’s mantle.
- When
- The minerals may have formed early in Earth’s history as a molten basal magma ocean cooled and crystallised.
- Where
- About 2,900 kilometres beneath the surface, near the boundary between the mantle and the liquid outer core.
- Why
- The research aims to explain where Earth’s water may be stored and how the planet obtained and retained it.
- Estimated water volume
- Equivalent to about two Pacific Oceans
- Proposed depth
- Approximately 2,900 kilometres below Earth’s surface
- Location
- Near the mantle–liquid outer-core boundary
- Candidate minerals
- Iron oxyhydroxides Fe5O12Hx and Fe7O12Hx
- Research method
- High-pressure, high-temperature experiments using diamond tips and lasers
- Publication
- Nature Geoscience
- Key limitation
- There is no proof that the mineral phases are present inside Earth