Banded iron formations
Due to the emergence of cyanobacteria during the Archean Eon, carbon dioxide began to be absorbed and oxygen released. With the rapid increase in photosynthetic organisms, the oxygen concentration on the earth gradually rose. However, in the beginning, due to the oxidation of the abundant ferrous ions in seawater, banded iron formations appeared. Currently, more than 80% of the earth’s iron deposits were formed during the late Archean Eon (2.5 billion years ago). When there was no more oxidizable matter on the surface, oxygen began to be released into the air, resulting in the so-called Great Oxidation Event (GOE), which represents an important time as the earth’s surface environment evolved from a reduced state to an oxidized state.
Banded iron formations are evidence that oxygen began to appear in the earth’s early atmosphere. When there was no oxygen on the surface, iron was mainly dissolved in a reduced state in seawater. Cyanobacteria released oxygen during photosynthesis and reduced iron combined with oxygen to form fine iron oxide particles, which were deposited on the seabed, with banding due to seasonal factors.
