Brazilian researchers find goethite survives in Earth's lower mantle

Brazilian scientists have provided the first direct evidence that goethite, the iron‑oxide mineral that gives many soils their brown hue, can survive the extreme pressures and temperatures found deep inside the Earth. Using a diamond anvil cell only 3 mm long, researchers trapped a microscopic impurity of goethite and subjected it to conditions that mimic those in the planet’s lower mantle. The mineral remained stable, demonstrating that it can endure the harsh environment of the Earth’s interior.

Goethite normally forms in soil and on the ocean floor from iron‑rich minerals in the presence of water, incorporating some of those water molecules into its crystal structure. The study’s findings suggest that, under high‑pressure conditions, goethite could act as a carrier, transporting water from the surface into the lower mantle where it may be released. This mechanism offers a new perspective on how water is distributed within the planet and could influence models of Earth’s deep water cycle.

The discovery highlights the resilience of surface minerals under extreme conditions and opens avenues for further research into the role of goethite and similar compounds in deep‑Earth processes. Understanding this transport mechanism may refine our knowledge of mantle chemistry, seismic activity, and the long‑term evolution of Earth’s water inventory.