The abundance of the element oxygen is not only crucial for life at the surface of the Earth, but also greatly affects the properties and dynamics of the interior of our planet.The combination of a highly oxidized atmosphere and a large reduced metallic core makes our Earth unique among the terrestrial planets, and has led to substantial variations and gradients in oxygen abundances in the rocky crust and mantle.Recent results from a range of research fields including mineralphysics, seismology, thermodynamic modelling and numerical geodynamic simulations have provided compelling evidence that the oxygen distribution in Earth's mantle is highly heterogeneous, with large oxygen-rich domains within a generally reducing mantle environment [1-3], with possible variations up to over 10 orders of magnitude expressed through oxygen fugacity.A novel deep super-oxidized form of FeO2, produced by pressure-induced decomposition of goethite (FeO2H) and releasing hydrogen, was recently revealed based on theoretical and experimental studies at the high pressure-temperature conditions present in Earth's lower-mantle [1].In addition, an oxygen-rich layer can be produced and thickened when water transported into the mantle by subducting slabs is brought into contact with the nearly inexhaustible metallic iron source in the core [2,4].