Archaean sulfur cycle

There are two reasons why it is likely that the Archaean sulfur cycle might have been very different from that which is observed in the modern. First, as will be discussed later in this chapter, the Archaean atmosphere had very low levels of oxygen, so that there was no oxidative weathering of sulfide in crustal rocks at this time. This means that no sulfate was delivered to the Archaean oceans through weathering and consequently the Archaean ocean was probably very low in sulfate. Second, the removal of sulfate from the ocean is bacterially mediated. The operation of this... 

Hence the Archaean sulfur cycle (Fig. 5.5) would comprise inputs into the atmosphere and oceans from volcanic gases and into the oceans from hydrothermal activity but not river-borne sulfate. In addition, in the anoxic oceans, the oxidative alteration of the ocean floor would not take place. Thus the surface sulfur reservoir would have been small and most sulfur recycled back into the mantle as sulfide minerals. The sulfate part of the sulfur cycle is unlikely to have been fully operational until the late Proterozoic (Canfield, 2004). 

Ono, S., Eigenbrode, J.L., Pavlov, A.A., Kharecha, P., Rumble, D., Kasting, J.F., and Freeman, K.H., 2003. New insights into Archaean sulfur cycle from mass-independent sulfur records from the Hammersley basin, Australia. Earth Planet. Sci. Lett., 213, 15-30. 

FIGURE 5.5 The modern sulfur cycle showing the fluxes in 1011 mol/yr (after Canfield, 2004). The parts of the cycle shown as dashed lines did not operate in the Archaean. 

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