Oxygen, iron, and sulfur geochemical cycles on early Earth: Paradigms and contradictions

The current understanding of the evolution of the atmosphere, hydrosphere, and biosphere on early Earth has been strongly influenced by the following six major paradigms for the geochemical cycles of oxygen, iron, and sulfur: (1) a dramatic change from a reducing to an oxidizing atmosphere at ca. 2.4-2.2 Ga, termed the "Great Oxidation Event" (GOE); (2) Fe-rich oceans until ca. 1.85 Ga; (3) a hydrothermal origin for the global oceanic Fe; (4) SO4 2-poor oceans before the GOE; (5) an atmospheric origin for the oceanic sulfur species; and (6) the existence of sulfi dic Proterozoic oceans. Each of the six paradigms has been built on other paradigms, such as those concerning: (1) the behavior of Fe during soil formation, (2) the environments and processes required for the formation of FeIII oxides in banded iron formations (BIFs), and (3) the origins of siderite and pyrite, as well as (4) the origin of anomalous isotope fractionation of sulfur (AIF-S) in Archean sedimentary rocks. Here, we show that.