What physical evidence supports great oxygen event theory
>>8971518
https://en.wikipedia.org/wiki/Great_Oxygenation_Event
banded iron formations (soluble ferrous iron turning into insoluble ferric iron in the oceans), absence of detrital pyrite and uranite (oxidizing atmosphere degrades those minerals during transport), no more mass-independent fractionation of sulfur isotopes (fractionation signal from UV is scrambled by reactions with oxygen in the atmosphere), etc.
Information on its Wikipedia entry