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

Abstract

Abstract Goethite, α‐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 Fe 2 O 3 , Fe 3 O 4 , Fe 5 O 7 , and novel Fe 7 O 10 and Fe 6.32 O 9 ). 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) ∼2.2 Ga ago. Rust was buried on the ocean floor and was transported into the mantle as a consequence of plate tectonics (started ∼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.