Scientists are transforming our understanding of planetary origins with growing evidence that Earth’s largest reservoir of water may be hidden far below the surface, locked inside solid rock for billions of years. Long believed to be relatively dry beneath its crust, Earth is now thought to have formed with a substantial internal water supply that remains trapped deep within Earth’s interior, reshaping theories about where planetary water came from and how it has influenced the planet’s long-term evolution and habitability.
This shift is driven by new research published in Science on December 11, which focuses on the behavior of bridgmanite—the most abundant mineral in the lower mantle. Under everyday conditions, bridgmanite appears dry, but under extreme temperatures and pressures similar to those present during Earth’s formation, it can incorporate far more water than scientists previously realized. Because bridgmanite dominates the lower mantle, this discovery suggests that a massive amount of water may be stored deep within Earth’s interior, potentially exceeding the volume of all surface oceans combined.
To reach this conclusion, researchers from the Carnegie Institution for Science, led by Wenhua Lu, used a laser-heated diamond anvil cell to recreate the intense conditions of the early planet. Their experiments reached temperatures above 3,700 Kelvin and pressures greater than 700,000 atmospheres, simulating the environment that existed as Earth’s primordial magma ocean cooled and crystallized. Under these conditions, bridgmanite absorbed increasing amounts of water as temperatures rose, indicating that water was preferentially retained in the mantle rather than being fully expelled to the surface during planetary differentiation.
These findings challenge long-standing assumptions about Earth’s water cycle, which has traditionally focused on surface reservoirs such as oceans, ice, and the atmosphere. If vast quantities of water are stored within Earth’s interior, the global water cycle must be redefined to include deep, long-term exchanges between the mantle and the surface. This hidden reservoir could help explain the unique chemical signatures observed in mantle plume volcanism, particularly in regions like Hawaii and Iceland, where magma rising from great depths appears to carry ancient, water-related characteristics.
The research also aligns with previous discoveries of water-bearing minerals such as ringwoodite in the mantle transition zone, strengthening the case that Earth’s water did not arrive solely through late-stage impacts from comets or asteroids. Instead, the results support a “wet accretion” model, in which water was incorporated into the planet during its initial formation. This suggests that Earth’s building blocks already contained hydrogen and oxygen, embedding water deep within the planet from the very beginning.
The implications extend beyond Earth. If rocky planets commonly form with internal water reservoirs, worlds that appear dry at the surface could still host significant hidden water stores. Such internal hydration could influence tectonics, volcanism, magnetic field generation, and long-term climate stability, expanding the criteria for planetary habitability. Although the lower mantle cannot be directly observed, seismic anomalies, geochemical evidence, and experimental advances increasingly point to a deeply hydrated Earth’s interior. As future studies refine these models, they may fundamentally change how scientists understand planetary evolution, internal dynamics, and the long-term regulation of surface conditions.
www.dailygalaxy.com/2025/12/scientists-just-uncovered-what-may-be-the-largest-water-reservoir-ever-found-buried-inside-earths-mantle/