Earth's Core Has Been Quietly Leaking Water for Billions of Years
For decades, geoscientists have treated Earth's metallic core and the rocky mantle above it as chemically isolated reservoirs that have barely exchanged material since the planet formed. A study published in Science Advances in October 2026 challenges that picture: the core, the authors argue, has been slowly releasing hydrogen — a key ingredient of water — into the surrounding mantle for billions of years.
The work comes from researchers at the University of Science and Technology of China, led by Yu Zhang and colleagues, published in October 2026 (DOI 10.1126/sciadv.aei4756). The team used machine-learning-accelerated "path-integral simulations" that capture the quantum behavior of atoms under the crushing pressures and searing temperatures of the deep Earth.
The evidence comes from the chemistry of volcanic rocks. The team measured the ratio of deuterium — heavy hydrogen — to ordinary hydrogen (the D/H ratio) in ocean island basalts from Baffin Island in Nunavut, Canada, and from Iceland. These rocks show unusually low D/H ratios, a fingerprint pointing to hydrogen dating back to Earth's earliest history rather than water recycled from the surface through plate tectonics. Such basalts are prized as natural probes of the deep mantle.
The proposed mechanism reaches back to the planet's birth. As iron sank to form the core, it preferentially absorbed lighter hydrogen from the primordial solar nebula, leaving the core depleted in deuterium. Over billions of years, that deuterium-poor hydrogen has been gradually leaking outward into the lower mantle, where it can end up as water locked inside minerals. The process continues today.
Earth's core accounts for roughly one-third of the planet's total mass, but the leak is minuscule — only a tiny fraction of material moved over billions of years. The authors stress that this slow exchange is unlikely to threaten the geodynamo or the stability of the magnetic field on any human timescale. Its main significance is enriching the deep Earth's budget of water and other volatile compounds.
The paper does not pin down a leak rate or the total amount of hydrogen transferred; those quantities, the authors note, will require further observation and experiment to confirm. The simulations so far support selective transfer across the core-mantle boundary rather than wholesale mixing, and ratios of helium-3 to helium-4, along with tungsten isotopes, may offer the next lines of evidence.