Chinese scientists have uncovered compelling evidence that Earth’s deep mantle once stored vast quantities of water during the planet’s earliest stages, offering new insight into how Earth evolved into a habitable world. The findings, published in the journal Science, suggest that the lower mantle acted as a massive ancient water reservoir more than four billion years ago.
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The research was carried out by scientists at the Guangzhou Institute of Geochemistry under the Chinese Academy of Sciences. Using advanced laboratory techniques, the team explored how water behaved as Earth cooled from a molten magma state into a solid planet. Their work addresses a long-standing scientific question about the fate of water during Earth’s early magma ocean phase.
At the centre of the discovery is bridgmanite, the most abundant mineral in the Earth’s lower mantle. Previously believed to have limited capacity to store water, bridgmanite was found to trap significant amounts of water under extreme conditions. The researchers recreated lower-mantle pressures and temperatures — reaching nearly 4,100 degrees Celsius — using a diamond anvil cell combined with laser heating.
Surprisingly, the experiments revealed that bridgmanite becomes more efficient at capturing water as temperatures rise, a finding that challenges earlier assumptions. This temperature-dependent behaviour means that, as early magma cooled and crystallised, enormous volumes of water could have been locked into the solid mantle.
According to the study, the deep mantle may have stored an amount of water ranging from 0.08 to one full modern ocean’s volume. Over billions of years, this hidden water was gradually released back to the surface through volcanic processes, contributing to the formation of oceans and sustaining Earth’s long-term water cycle.
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Scientists say the discovery provides a missing link in understanding Earth’s transformation from a fiery, molten body into a planet capable of supporting life. It also reshapes ideas about the role of the deep interior in regulating surface conditions over geological time.