Talk:Banded iron formation

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Deleted text[edit]

please give a citation for the assertion that the total oxygen worldwide in banded iron formations is about 20 times the amount in the atmosphere.

  • The following text has been perhaps hastily deleted: "Banded iron formations and calcite formations were deposited at the same time from magma that also formed the first land mass made of granite. These three rock formations were distilled out of the magma in a very different ocean than we see today. It was hot and rich in carbon dioxide and magma give up iron and calcium to the early ocean at a much greater rate than it does now. What was left was granite which is less dense than magma and so to tended to rise and form the bed rock that the iron settled upon."
Some such characterization of the iron-rich ocean waters would help make this article less impenetrable. --Wetman 07:19, 5 December 2006 (UTC)

I removed it because it was simply very confusing and rather full of errors - it made the subject even more impenetrable. Now, I agree that the article is in need of some clarification and de-impenitralation. Someday maybe... Vsmith 16:38, 5 December 2006 (UTC)

The author of the above bit has questioned my removal (on my talk page). So I will address some of the errors and confusing points.
Banded iron formations and calcite formations were deposited at the same time from magma that also formed the first land mass made of granite.
The BIFs were sedimentary deposits - not magamtic. Calcite formations? are not there as far as I know. The carbonates associated with BIFs were siderite and dolomite. The BIFs are associated with greenstone belts, areas of metamorphosed basaltic volcanism. I don't think they were directly related to granites.
...rock formations were distilled out of the magma in a very different ocean than we see today.
They were not distilled out of the magma. The ocean was different in that it was lacking in oxygen and had abundant reduced iron is solution. Perhaps the most abundant component of BIFs is the chert. It has been proposed that the alternating iron oxide layers and chert layers represent a fluctuating oxygen content as photosynthesising algae waxed and waned. The iron has been postulated to be of hydrothermal origin, whereas the silica for the chert layers may be either of hydrothermal or continental weathering origin.
What was left was granite which is less dense than magma and so to tended to rise and form the bed rock that the iron settled upon.
This sentence is essentially meaningless - the iron depleted magma rose and the BIFs derived from it was deposited on the granite?
Now maybe I'll get around to adding more detail to the article based on some of my comments above and based on some good references available - someday. Vsmith 02:11, 7 December 2006 (UTC)
Also, the added bit was not sourced and neither are my comments above (largely from memory). When I get 'round to-it, (adding to the article that is) I'll back up my memory with solid references. Cheers, Vsmith 02:20, 7 December 2006 (UTC)
"The banded iron formations are our first glimpse into an aspect of Earth's paleoecology." I'm an amateur, but wouldn't that make a useful topic sentence? --Wetman 16:47, 5 December 2006 (UTC)
Something along those lines would work - tie in to atmospheric evolution as well. Vsmith 02:11, 7 December 2006 (UTC)

I will admit the facts are confusing and will attempt to fix the problem. The first thing to consider is the current placement of the CO2. It is very clear there is a lot of CO2 in the rock formations made of calcium and magnesium. That CO2 came from somewhere as the chemical reactions occured. The reactions only happen when the right environment is in place. The ocean is where it happened and that means the ocean was very different than it now is. The magma is the source of calcium and magnesium and when CO2 is available and given the right environment calcite and dolemite form. The iron also in the magma desolves as you say into an iron rich ocean and no oxygen. Now, doing a bit of math we find the total CO2 was ~10E20 kilograms or more. All that CO2 was in the atmosphere in the beginning. That means the atmosphere was more than 20 times as dense as now so the pressure at sea level was 20 times more than now. You are not going to find a lot of detail about any of this except in the rocks and I only read what others say they find as I see nothing when I look at the rocks. If they are right then at some time about 4bya there was no land and then land started to rise from the seabed as granite because granite is less dense than magma. The BIFs were then able to settle out in shallow water. Calcite/dolemite also formed at that time as a part of the same complex process.—Preceding unsigned comment added by User:Jimhmeyer (talkcontribs) 03:06, 12 December 2006 --Jo (talk) 21:02, 8 March 2008 (UTC)