Scientists uncover how Earth’s mantle locked away vast water in early magma ocean

Some 4.6 billion years ago, Earth was nothing like the gentle blue planet we know today. Frequent and violent celestial impacts churned its surface and interior into a seething ocean of magma—an environment so extreme that liquid water could not exist, leaving the entire planet resembling an inferno.

Since 70% of Earth's surface is now covered in oceans, the mystery of how water was survived and preserved in our planet from an early molten to a mostly solid state,  has long been a subject of scientific study.

Recently, a team of researchers led by Prof. DU Zhixue from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences (GIGCAS) has discovered that substantial amounts of water could have been efficiently "locked away" deep within the mantle as it crystallized from a molten state.

The researchers' findings, published in Science on December 11, are reshaping our understanding of water storage and distribution in the deep Earth. Specifically, their research revealed that bridgmanite, which is the most abundant mineral in Earth's mantle, acts like a microscopic "water container"—making it possible for early Earth to retain a substantial amount of water in the mantle as the planet solidified.

This early-retained water, the team argues, may have been critical to transforming Earth from a fiery inferno into a habitable world.

Previous studies, which relied on relatively low-temperature experimental conditions, suggested that bridgmanite had limited water storage capacity. The researchers wanted to test this hypothesis but faced two major challenges. First, they needed to simulate the extreme conditions found at depths exceeding 660 kilometers in a laboratory. Second, they had to accurately detect water signals in bridgmanite samples—some smaller than one-tenth the width of a human hair—at concentrations as low as a few hundred parts per million.

They overcame these obstacles by building a diamond anvil cell experimental setup equipped with laser heating and high-temperature imaging. This self-developed, ultra-high-pressure simulation device raised experimental temperatures dramatically—to an extreme of ~4,100 °C. This system successfully recreated deep mantle conditions and allowed for precise measurement of equilibrium temperatures, laying the foundation for understanding temperature's role in how water is taken up by minerals.

In addition, using the advanced analytical platforms of GIGCAS, the researchers applied techniques such as cryogenic three-dimensional electron diffraction and NanoSIMS. In collaboration with Prof. LONG Tao from the Institute of Geology of the Chinese Academy of Geological Sciences, they also integrated atom probe tomography (APT). Together, these tools enabled the development of innovative methods for analyzing water at the micro- to nanometer scale, effectively equipping the microscopic world with ultra-high-resolution "chemical CT scanners" and "mass spectrometers." This technology let the team clearly visualize water distribution in tiny samples and confirm that water is structurally dissolved in bridgmanite.

The team's data revealed that bridgmanite's "water-locking" capacity (measured by its water partition coefficient) increases significantly with rising temperature. This means that during Earth's hottest "magma ocean" phase, crystallizing bridgmanite could have retained far more water than previously thought, directly overturning the long-held view that the deep lower mantle is nearly dry.

Building on this discovery, the team modeled the crystallization of the magma ocean. Simulations show that, thanks to bridgmanite's strong water-locking ability under early high temperatures, the lower mantle became the largest water reservoir in the solid mantle after the magma ocean solidified. Its storage capacity, the model indicates, could be five to 100 times greater than earlier estimates. The total amount of water retained in the early solid mantle may even have equaled 0.08 to 1 times the volume of all modern oceans.

This deeply buried water was not a static reserve. Instead, it acted as a "lubricant" for Earth's massive geological engine: It lowered the melting point and viscosity of mantle rocks, promoting internal circulation and plate motion and providing the planet with sustained evolutionary vitality. Over time, this sequestered water was gradually "pumped" back to the surface through magmatic activity, contributing to the formation of Earth's primordial atmosphere and oceans. The "spark of water" sealed within Earth's early structure, the researchers noted, likely served as the crucial force that transformed our planet from a magmatic inferno into the blue, life-friendly world we know today.