Today, banded iron formations, a type of sedimentary rock found in many locations, provides evidence for the dramatic increase in oxygen released by cyanobacteria. oxygen reacted with iron dissolved in the ocean. this created black iron oxide minerals (like hematite and magnetite). these minerals, together with reddish-colored chert (a very fine-grained quartz that contains small amounts of iron), precipitated out of solution, collected at the sea floor, and eventually turned into banded iron formations.

the majority of banded iron formations were formed about 2.2 billion years ago during the precambrian eon. during this time, widespread iron oxidation, in large part due to oxygen production by cyanobacteria, provided the minerals that make up banded iron formations.

take a look at the image showing banded iron-rich rocks deposited during the precambrian eon. the statements below describe conceptual relationships between iron-rich deposits and earth’s early atmosphere. determine if these statements are true or false.