Answer:
Iron oxides appeared after the emergence of cyanobacteria.
Explanation:
The composition of Earth's atmosphere in the first couple of billions of years of its existence was nothing like the atmosphere of today. This had a big influence on the processes that were taking place, or rather what processes and to what extent could have happened in those conditions. One big difference between the atmosphere then and after is the levels of oxygen.
Until the appearance of cyanobacteria, the oxygen levels in Earth's atmosphere were very low, and the same goes for the oceans. With a lack of oxygen, the process of oxidation was absent as well. The cyanobacteria though managed to produce oxygen, and this was on such a high scale that they changed the composition of Earth's atmosphere and the oceans. Not just that this enabled complex lifeforms to develop, but it also enabled the process of oxidation. Iron oxides for example occurred only after cyanobacteria appeared, and this can easily be seen when dating the oldest iron oxides and compare that age with the appearance of cyanobacteria.
