Why are banded iron formations limited to the Precambrian geological record??

Question

Does anyone know?? Also why do they not form today??

Answer 1

It has to do with the composition of the atmosphere at that time. I have included an excerpt from the referenced web site.

This was a time when the atmosphere was a choking mix of nitrogen and carbon dioxide. In the shallow anoxic seas lapping upon the early continents, the cyanobacteria were in Fat City with the world to themselves, breathing carbon dioxide and making oxygen as a waste product. Ferrous iron in the water scavenged that poisonous waste, turned into solid minerals—magnetite and hematite—and settled in vast, thin layers.
For over 2 billion years this went on, until the iron ran out, and then the oxygen bubbled up into the atmosphere. The clear, oxygenated atmosphere we know dates from about 1,700 million years ago, after two-thirds of Earth history. The vast layers of iron minerals stayed behind in the banded iron formations, or BIFs. Those are the algal legacy that we mine today. Nowadays, such iron deposits can form only in the airless bottoms of bogs. "Bog ore" was the main source of iron in ancient and medieval times.

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Answer 2

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Answer 3

The PreCambrian is when life was just starting to appear. Life was 1-celled organisms and most complexity to be seen was in the stromatolites (living ones to be found off the coast of Australia)--mushroom-like colonies of microbes. Way back then, Earth's atmosphere was very different than it is now: almost no oxygen, high levels of carbon dioxide, methane, and other gases that are toxic to us today. Technically, oxygen is corrosive (ie, rust), and those early one-celled organisms viewed oxygen as a poison. The problem is that those little guys gave off oxygen as a by-product of their digestive processes. Oxygen levels would build up to toxic level, kill off a bunch of microbes, and the gas levels would drop. This would repeat countless times until the microbes could handle oxygen and the gas levels balanced out. The red bands in the banded formations is from those time periods when oxygen levels were high--the iron literally rusted; while the black bands are times of low oxygen levels.
Banded formations can't form today since our atmosphere has balanced itself out, more-or-less, and nothing less than every photosynthetic based life form being wiped out will chance that, since plants are pumping out all the oxygen we aerobes need.

Answer 4

If you don't accept the current theory on this you are not alone. They say th atmosphere was low in oxygen and that lead to the BIFs but it seems more logical there was many times more CO2 in the atmosphere because there is so much CO2 now locked up in other rock formations. The very rich CO2 atmosphere made life impossible before most of it was removed when calcite formations and BIFs came into being. After that life evolved. BIFs don't form now because very little CO2 is in the atmosphere. Its very simple don't you think?

Answer 5

dah -because Jesus created the earth that way-why dont we get new layers on the earth-because the earth was created with age-how old was adam-dah -he had aged bones when he was created- or he came from a one celled omeba with a perfect dna to reproduce itself -but a major miracle -well Jesus could have done that too--but no scientist could let alone a billion accidents-unless its in jest in comedy.

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