Schopf in Cradle of Life says in part:
Yet the presence of these remarkable deposits does not mean the oceans were oxygen-rich. On the contrary, BIFs were nearly always deposited in large basins, hundreds of kilometers in length and breadth, and the dissolved ferrous iron from which BIFs form could be spread over such vast distances only if carried by waters that were oxygen-poor. Huge amounts of molecular oxygen were pumped into the environment by oxygenic (cyanobacterial) photosynthesis, but except locally, near where it was produced, amounts of oxygen were kept low by its capture and rapid burial in the oxide minerals of BIFs.You forgot to deal with the pyrites and I forgot to mention the uraninite. From Icon of Obfuscation:
Chapter 2: Miller-Urey experiment
Prebiotic Oxygen. A key question in origin-of-life research is the oxidation state of the prebiotic atmosphere (the current best guess is that the origin of life occurred somewhere around 4.0-3.7 bya (billion years ago)). Wells wants you to think that there is good evidence for significant amounts free oxygen in the prebiotic atmosphere (significant amounts of free oxygen make the atmosphere oxidizing and make Miller-Urey-type experiments fail). He spends several pages (14-19) on a pseudo-discussion of the oxygen issue, citing sources from the 1970's and writing that (p. 17) "the controversy has never been resolved", that "Evidence from early rocks has been inconclusive," and concluding that the current geological consensus -- that oxygen was merely a trace gas before approximately 2.5 bya and only began rising after this point -- was due to "Dogma [taking] the place of empirical evidence" (p. 18). None of this is true (see e.g. Copley, 2001).
Certain minerals, such as uraninite, cannot form under significant exposure to oxygen. Thick deposits of these rocks are found in rocks older than 2.5 bya years ago, indicating that essentially no oxygen (only trace amounts) was present. On page 17 Wells notes that uraninite deposits have been found in more recent rocks, but neglects to mention to his readers that these only occur under rapid-burial conditions, whereas ancient deposits of uraninite occur in slow deposition conditions, for example in sediments laid down by rivers, so that the minerals were exposed to atmospheric gases for significant periods of time before burial.
'Red beds' are geologic features containing highly oxidized iron (rust) indicative of high amounts of oxygen. Wells (p. 17) notes that red beds are found before 2 bya, but fails to mention that the temporal limit of red beds is just a few hundred million years before 2 bya.
Wells doesn't even mention the evidence that banded iron formations (incompletely oxidized iron indicative of ultralow-oxygen conditions) are very common prior to 2.3 bya and very rare afterwards.
Wells also doesn't mention that early paleosols (fossil soils) from about ~2.5 bya contain unoxidized cerium, impossible in an oxygenic atmosphere (e.g., Murakami et al., 2001).
Finally, Wells doesn't mention to his readers that pyrite, a mineral even more vulnerable to oxidation than uraninite, is found unoxidized in pre-2.5 bya rocks, and with significant evidence of long surface exposure (i.e. grains weathered by water erosion; e.g. Rasmussen and Buick, 1999).
Why does Wells leave out the converging independent lines of geological evidence pointing to an anoxic early (pre ~2.5 bya) atmosphere?
I don't know. I did not cite Wells. I cited a link to Duke University chemistry resources. This was from a link JediGirl gave. You apparently didn't read it or you may not understand oxidation/reduction. I answered your problem with the atmosphere and BIF. Please note: Oxygen is not needed for oxidation to occur or for something to be considered oxidizing.