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) SO 4 2− -poor oceans before the GOE; (5) an atmospheric origin for the oceanic sulfur species; and (6) the existence of sulfidic 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 Fe III 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 some of the paradigms contradict each other, and that each has serious flaws (contradictions, problems) when they are compared to a variety of observations (geological, mineralogical, or geochemical data from natural samples; laboratory experimental data; results of theoretical studies). In contrast, all of these observations are better explained by the Dimroth-Ohmoto model for Earth's evolution, which postulates that a fully oxygenated atmosphere-ocean system developed by ca. 3.5 Ga. Examination of the available data from natural and experimental systems has also led us to suggest the following: (1) The geochemical cycles of O, Fe, and S (and other redox-sensitive elements) through the atmosphere–ocean–oceanic crust–mantle–continental crust have been basically the same as today since at least ca. 3.5 Ga. (2) The anaerobic and aerobic microbial biospheres, both in the oceans and on land, developed by ca. 3.5 Ga, playing an important role in the geochemical cycles of nutrients and other elements. (3) The geochemistry of sedimentary rocks (shales, carbonates, cherts) has been basically the same since ca. 3.5 Ga. (4) Fe III oxides in BIFs were formed by reactions between locally discharged Fe 2+ - and silica-rich submarine hydrothermal fluids and O 2 -rich deep seawater. (5) Magnetite in BIFs was formed during high-temperature diagenetic stages of BIFs through reactions between primary goethite or hematite and Fe 2+ -rich hydrothermal fluids. (6) BIFs were formed throughout geologic history. (7) Sulfidic oceans (i.e., the “Canfield ocean”) did not exist during the Proterozoic Eon. However, regional sulfidic seas, like the Black Sea, have existed in globally oxygenated oceans throughout geologic history. (8) The primary carbonate in Archean oceans, as in younger oceans, was Fe-poor calcite. Furthermore, (9) the pre–1.8 Ga atmosphere was CO 2 rich with the p CO 2 level greater than ~100 present atmospheric level (PAL). CO 2 alone provided the green-house effect necessary to compensate for the young Sun's lower luminosity. (10) The Archean pH values were 4.0–4.5 for rainwater, between 4.5 and 6.0 for river water, and 7.0 ± 0.5 for ocean water. The oceans were saturated with calcite but under-saturated with siderite. (11) The δ 18 O of Archean oceans was ~0‰, as today. (12) Fe-rich carbonates (siderite, ankerite) have formed during the diagenesis of sediments throughout geologic history by reactions between the primary calcite and Fe 2+ -rich solutions, either hydrothermal solutions or those derived from biological or abiological dissolution of Fe III -(hydr)oxides within the sediments. Other suggestions include: (13) The ranges of δ 34 S values of pyrite and sulfates in Archean sedimentary rocks are much larger than those quoted in the literature and comparable to those in Proterozoic sedimentary rocks. (14) Pyrites in organic C–rich black shales associated with BIFs were formed by a reaction between Fe 2+ - and SO 4 2− -rich hydrothermal solutions and organic C–rich shales during early diagenetic stages of the host sediments. This reaction also created AIF-S in the pyrite and the residual SO 4 2− . (15) The AIF-S signatures in Archean and younger rocks were not created by the ultraviolet photolysis of volcanic SO 2 in a reducing atmosphere. AIF-S signatures are not evidence for a reducing atmosphere. (16) Contrary to a popular belief that AIF-S–forming events ceased at ca. 2.45 Ga, AIF-S was also formed at later geologic times. (17) The presence of AIF-S signatures in some pre–2.4 Ga rocks, but the lower abundance of AIF-S in post–2.4 Ga rocks, may reflect changes in the mantle-crust dynamics, including changes in the thickness and movements of oceanic lithosphere.

Geological and geochemical characteristics of banded iron formations (BIFs) suggest that they formed by mixing locally (or regionally) discharged submarine hydrothermal fluids with local seawater, rather than by upwelling deep ocean water. Submarine hydrothermal fluids typically evolved from local seawater by acquiring heat, metals, and sulfur during deep circulation through a variety of rocks (e.g., volcanics, evaporites) in greenstone terranes that developed under a variety of tectonic settings. In general, when the fluids were heated above ∼350 °C, they may have produced Cu- and Zn-rich volcanogenic massive sulfide deposits (VMSDs), whereas those heated less than ∼200 °C were generally poor in H 2 S and heavy metals, except Fe, and may have subsequently produced BIFs. Depending on the salinity contrast between discharging hydrothermal fluids (evolved seawater) and local seawater, hydrothermal fluids may (1) mix rapidly with local seawater to form smoker-type BIFs or (2) create a metal- and silica-rich brine pool, mix slowly with the overlying water body, and form brine pool-type BIFs. BIFs associated with VMSDs and volcanic rocks generally belong to smoker-type BIFs; many formed at seawater depths >2.5 km. Large BIFs, including the 2.6–2.4 Ga BIFs in the Hamersley Basin, Australia, the 2.5 Ga Kuruman IF in South Africa, and the 1.87 Ga BIFs in the Lake Superior region, United States-Canada, belong to brine pool-type BIFs. The Hamersley Basin and possibly other large BIF-hosting basins were probably land-locked seas (like the Black Sea) where river waters diluted the surface water zone and the underlying water bodies were anoxic. During the accumulation of a BIF sequence, the dominant Fe mineralogy frequently changed from ferric (hydr)oxides (oxide BIFs) to siderite (carbonate BIFs) and to pyrite (sulfide BIFs). Such changes were probably caused by changes in the relative amounts of dissolved O 2 (DO), ΣCO 3 2− , and ΣS 2− in local seawater. From the Fe 2+ -O 2 mass balance calculations for the formation of iron oxides in smoker-type BIFs, and the relationship between the atmospheric pO 2 and oceanic O 2 depth profile, we conclude that the atmosphere and oceans have been fully oxygenated since ca. 3.8 Ga, except in local anoxic basins. Thermodynamic analyses of the formational conditions of siderite and analyses of the carbon isotopic composition of siderite associated with major BIFs suggest that the pre–1.8 Ga atmosphere was CO 2 -rich (pCO 2 >100 PAL) and CH 4 -poor (pCH 4 ≈ 10 ppm); therefore, CO 2 , rather than CH 4 , was the major greenhouse gas throughout geologic history. After a decline of hydrothermal fluid flux, BIF-hosting basins generally became euxinic (H 2 S-rich) because of the increased activity of sulfate-reducing bacteria (SRB) and SO 4 2− -rich seawater, and thereby accumulated organic carbon-rich and pyrite-rich black shales (sulfide-type BIFs). The SO 4 2− contents and SRB activity in the oceans have been essentially the same since ca. 3.8 Ga. The Archean oceans were most likely poor in both Fe 2+ and silica, much like modern oceans. Our study also suggests that diverse communities of organisms, including cyanobacteria, SRB, methanogens, methanotrophs, and eukaryotes, evolved very early in Earth's history, probably by the time the oldest BIFs (ca. 3.8 Ga) formed. BIFs have been found in rocks of all geologic age. Therefore, they cannot be indicators of an anoxic atmosphere and/or anoxic oceans as suggested by many previous researchers. Instead, BIFs indicate that the atmosphere and ocean chemistry have been regulated at present compositions (except pCO 2 ) through geologic history by interactions with the biosphere. The general trend of declining size and abundance of BIFs with geologic time reflects the cooling history of Earth's interior.