The enormous amount of banded iron formation deposited during the period of 2.5 to 2.0 billion years ago signifies a transition from oxidizing to reducing atmosphere on Earth.

Question

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The banded iron formations indicate a transition from a reducing to an oxidizing atmosphere, as they formed when oxygen produced by photosynthetic organisms reacted with iron in the oceans.

The Enormous Amount of Banded Iron Formation Deposited During the Period