How did the Banded Iron Formations Form?
The atmosphere on early Earth had little oxygen, and therefore little oxygen was dissolved in the ocean water. This allowed for iron to dissolve in the water readily, but iron requires an oxidating chemical reaction to precipitate. This creates a problem… How was the iron oxidized? Organic Theory: Photosynthesizing bacteria “grabbed” an iron atom (presumably with the oxygen molecule they release), which then started to form a crystal, growing inorganically and dropping to the ocean floor. There was a discovery in 1993 of purple bacteria (cyanobacteria) that use photosynthesis to break up iron carbonate dissolved in water and precipitate oxidized iron as a by-product. This is strong evidence for this theory. Also see below, banded iron formations and stromatolites. Inorganic Theory: UV radiation gave the energy to form an iron ore compound in the upper regions of the oceans, which then fell to the ocean floor. This happenned slowly over the archean and early proterozoic as photosynthe
