The deposition of banded iron formations during the Proterozoic Eon tells us that large amounts of iron settled out of the ________ as the result of rising atmospheric oxygen concentrations.

Question

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Banded iron formations are sedimentary rocks that are mainly composed of alternating layers of iron oxides and chert. They were deposited in the Earth's oceans between 2.5 and 1.8 billion years ago during the Proterozoic Eon. At that time, the Earth's atmosphere had very low oxygen levels. However, as oxygen began to build up in the atmosphere, it reacted with iron dissolved in the oceans to form insoluble iron oxide minerals that sank to the seafloor and accumulated to form banded iron formations. Therefore, the correct choice is B, oceans.

The Deposition of Banded Iron Formations During the Proterozoic Eon