Both the presence of banded iron formations and red beds are evidence that the atmosphere and hydrosphere changed from oxidizing to reducing in the Proterozoic.

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Banded iron formations indicate a transition from a reducing to an oxidizing atmosphere in the early Earth, while the presence of red beds signifies an already oxidized atmosphere and hydrosphere, not a change from oxidizing to reducing.

Both the Presence of Banded Iron Formations and Red Beds