Super-Deep Diamond Reveals Water Transport to Earth's Lower Mantle

A microscopic mineral pocket sealed inside a 3-millimeter diamond from Juina, Brazil, provides the first direct evidence that the mineral goethite can transport water into the Earth's lower mantle. Researchers analyzed the super-deep diamond using advanced synchrotron light techniques at the Sirius particle accelerator facility operated by the Brazilian Synchrotron Light Laboratory. The research team demonstrated that goethite, an iron oxyhydroxide typically found in soils and ocean floors, can survive extreme temperatures ranging from 877 to 1,827 degrees Celsius and pressures between 35 and 57 gigapascals. These findings challenge the traditional view that goethite decomposes near the surface and cannot endure subduction processes into the deep mantle. By remaining protected within deep fractures of cool oceanic plates, goethite can descend beyond 400 kilometers before transforming into hematite, magnetite, and water. This mechanism reveals a viable pathway for surface water to reach deep interior regions of the Earth previously thought incapable of storing significant moisture. Scientists can leverage these insights to better understand planetary water cycles and mantle dynamics. The study highlights the efficacy of using non-destructive synchrotron X-ray microtomography and diffraction to unlock geological secrets preserved inside natural diamond inclusions.