Cu2O is oxidized and reduced. It lost an electron in CuSO4 for the 2+ charge, but it gained an electron in Cu to go from the 1+ charge to a neutral charge. This is dismutation (aka disproportionation)
The formation of the tertiary atmosphere, with the re-arrangements of the plates, took that influenced the long term evolution of the planet that transferred the carbon dioxide to the large continental stores and the surplus oxygen came into formation about 2.4 billion years ago during the massive oxygenation event that leads to the appearance at the end of the banded iron formations.
The process of photosynthesis also added and reduced the material that reduces the oxidation of the atmosphere and kept ion place till 15% of the Precambrian period had ended.