Chemical Stability of FeOOH at High Pressure and Temperature, and Oxygen Recycling in Early Earth History**

Goethite, alpha-FeOOH, is a major phase among oxidized iron species, commonly called rust. We studied the behavior of iron (III) oxyhydroxide up to 81 GPa and 2100 K using in situ synchrotron single-crystal X-ray diffraction. At high pressure-temperature conditions FeOOH decomposes forming oxygen-rich fluid and different mixed valence iron oxides (previously known phases of Fe2O3, Fe3O4, Fe5O7, and novel Fe7O10 and Fe6.32O9). Rust is known to form as a byproduct of anoxygenic prokaryote metabolism that took place massively from about 3.8 billion years (Ga) ago until the Great Oxidation Event (GOE) similar to 2.2 Ga ago. Rust was buried on the ocean floor and was transported into the mantle as a consequence of plate tectonics (started similar to 2.8 Ga ago). Our results suggest that recycling of rust in Earth's mantle contributes to redox conditions of the early Earth and formation of oxygen-rich atmosphere.

Automated summary

The study found that goethite decomposes into oxygen-rich fluid and different iron oxides under high-pressure and high-temperature conditions. Goethite, formed from about 3.8 billion years ago until 2.2 billion years ago, was transported into the mantle through plate tectonics.