Banded iron formations indicate that there were oxygen-rich and oxygen-poor episodes during Earth's early atmosphere. Banded iron formations first appear in the Archean, 3 billion years ago. Unbanded iron deposits (red beds) from the Proterozoic, 1.8 billion years ago, indicate that the atmosphere became oxygen rich and that oxygen-poor episodes were no longer prevalent.
The Archean atmosphere is believed to have been free of free oxygen. Banded iron formations did not occur till near the end of the Archean period.
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BIFs are associated with the oxygenation of Earth's atmosphere, over vast periods of time, in Earth's distant past. They are also a vast storehouse of the element iron (mainly in the form of the minerals hematite and magnetite), and are mined for such.
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The Archean atmosphere is believed to have been free of free oxygen. Banded iron formations did not occur till near the end of the Archean period.
Banded iron formations indicate that there were oxygen-rich and oxygen-poor episodes during Earth's early atmosphere. Banded iron formations first appear in the Archean, 3 billion years ago. Unbanded iron deposits (red beds) from the Proterozoic, 1.8 billion years ago, indicate that the atmosphere became oxygen rich and that oxygen-poor episodes were no longer prevalent.
Oxygen
Banded iron formations (BIFs) are cherts (a form of quartz - SiO2) that exhibit an alteration of rust-red and gray bands. The rust-red bands represent oxygen-rich episodes and are colored by ferric iron oxide (Fe2O3) and the gray bands represent oxygen-poor episodes in Earth's early atmosphere. The first appearance of BIFs was in the Archean, 3 billion years ago. Unbanded iron deposits first appear in the Proterozoic, 1.8 billion years ago. Banded iron formations are the largest source for mined iron. ----------------------------------------------------------------------------------------------------------- Banded Iron Formations are sedimentary rocks deposited in Earth's early oceans. Originally Earth had no Oxygen in its atmosphere or oceans and the oceans were full of Iron salts. As life began to establish on Earth it started in the Oceans and as a waste product it produced Oxygen (from photosynthesis). This oxygen reacted immediately with the Iron salts dissolved in the water and Iron Oxide precipitated out to form the banded Iron formations. This went on for billions of years until all the Iron was gone and the Oxygen began to be released into the atmosphere.
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Because the Earth's first atmosphere/ocean system didn't have free oxygen, dissolved iron accumulated in the oceans, giving them a green color. As oxygen became available, it combined with the iron and settled to the sea floor to form banded iron formations (BIFs). Once the iron was "rusted" out of the water column, the ocean color changed from green to blue.
BIFs are associated with the oxygenation of Earth's atmosphere, over vast periods of time, in Earth's distant past. They are also a vast storehouse of the element iron (mainly in the form of the minerals hematite and magnetite), and are mined for such.
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J. E. Maynard has written: 'The origin of the precambrian banded iron formations'
It was laid down when earths oceans first acquired oxygen in the Precambrian
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Yes, banded can be a past-tense form of the verb band. As in, "They banded together to face the challenge."