Reservoirs of primordial water may lie deep beneath Earth’s surface
A new study by Chinese researchers points to the existence of sizable, undiscovered reservoirs of primordial water buried many kilometers below the planet’s crust.
Using an innovative approach to simulate the extreme conditions 660 kilometers underground—at high heat and pressure—the team found that bridgmanite, the mantle’s most abundant mineral, can hold a substantial amount of water at temperatures reaching about 4100 degrees.
The results, published in Science on Friday, challenge conventional views of how water is stored and distributed in the deep Earth. They also suggest that water retained during early Earth history could have played a pivotal role in cooling the planet from a molten, inhospitable state to a world capable of supporting life.
Led by Du Zhixue of the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS), the researchers propose that large quantities of water could have become trapped deep in the mantle as the magma ocean solidified.
Earth 4.6 billion years ago was far from a tranquil blue marble. Frequent, violent impacts kept the surface and interior in a turbulent, molten state. Liquid water could not exist amid such heat, leaving the young planet a raging inferno.
As this primordial magma ocean cooled and crystallized, solid minerals formed the mantle. Bridgmanite—the first and most abundant mantle mineral, comprising more than half of the mantle’s mass—may have functioned as a tiny, natural water container, according to the GIGCAS statement.
The mineral’s capacity to “lock” water would determine how much water could transition from the molten stage into solid Earth, the researchers say.
By modeling the crystallization of the early magma ocean, the team found that bridgmanite’s strong water-locking ability at high temperatures would make the lower mantle the planet’s largest solid-water reservoir after solidification.
Earlier work, based on cooler conditions, had suggested bridgmanite’s water-storage potential was modest. However, the Guangzhou team pushed temperatures up to 4100 degrees with a self-developed ultra-high-pressure experimental setup, showing that water-locking increases with temperature and could be 5 to 100 times greater than prior estimates.
Estimates indicate the amount of water trapped in the early solid mantle could equal about 0.08 to 1 times the volume of all oceans we have today.
The researchers emphasize that this deeply buried water is not a static stash. It likely acts as a “lubricant” for Earth’s vast geodynamic engine, lowering rock melting points and viscosity, enabling mantle convection and plate motion, and providing enduring geochemical vitality.
Over geological time, much of this water would gradually migrate back toward the surface via magmatic processes, contributing to the formation of the primordial atmosphere and oceans.
GIGCAS notes that the water sealed within Earth’s early interior may have been the decisive catalyst that helped transform the planet from a fiery, magma-dominated world into the blue, life-supporting Earth we know today.
