A new study suggests that Earth's early molten phase preserved water deep in its mantle through bridgmanite, preventing loss to space. Led by researchers at the Chinese Academy of Sciences, the findings explain how this hidden reservoir contributed to the planet's evolution into a water-rich world. Published in Science, the research challenges previous views on the mantle's dryness.
Earth's formative years, about 4.6 billion years ago, were marked by intense cosmic impacts that turned the planet into a molten inferno. A global magma ocean dominated the surface, with temperatures too extreme for liquid water to exist, raising questions about how today's oceans, covering 70% of the surface, came to be.
A team led by Prof. Zhixue Du from the Guangzhou Institute of Geochemistry at the Chinese Academy of Sciences has proposed a solution. Their research, detailed in the December 11, 2025, issue of Science, demonstrates that bridgmanite—the predominant mineral in the lower mantle—can store substantial water under high-heat conditions. Earlier experiments, limited to lower temperatures, underestimated this capacity, but the new work used advanced tools to simulate depths over 660 kilometers, reaching temperatures up to 4,100 °C.
Employing a diamond anvil cell with laser heating, along with techniques like cryogenic three-dimensional electron diffraction, NanoSIMS, and atom probe tomography, the scientists confirmed water's structural integration into bridgmanite. The mineral's water partition coefficient rises sharply with temperature, implying that during the magma ocean's cooling, bridgmanite trapped far more water than thought—potentially 0.08 to 1 times the volume of modern oceans.
This subterranean vault influenced Earth's geology profoundly. The stored water reduced mantle rock viscosity, facilitating convection and plate tectonics. Over eons, volcanic processes released it, aiding the creation of the atmosphere and surface oceans. As co-author Wenhua Lu and colleagues note in their paper 'Substantial water retained early in Earth’s deep mantle,' this mechanism was crucial for transforming a fiery proto-planet into a habitable one.
The discovery reframes the lower mantle not as arid, but as a vital water repository, with implications for understanding planetary habitability elsewhere.