Geochemical and cosmochemical cycles involving sulfur, sulfide, sulfite and sulfate

Abstract

Raman spectra• of aqueous systems containing sulfur dioxide, elemental sulfur and sulfate indicate that the equilibrium between these species is catalyzed by elemental sulfur. Therefore, dynamic equilibrium can be expected under conditions prevalent on Venus, on Io and in epigenic sulfur deposits.

Geochemical and Photochemical Constraints on S[IV] Concentrations in Natural Waters on Prebiotic Earth

“…However, our data do clearly favor one family of literature reports of anoxic S[IV] lifetime over the other, contradictory literature report. Specifically, even the fastest‐decaying of our S[IV] samples shows S[IV] lifetimes ≥1 year, favoring the literature reports indicating long S[IV] lifetimes (Cohen et al., 1982; Halevy et al., 2007; Meyer et al., 1979, 1982; Petruševski et al., 2013) over the literature report indicating short (∼10 days) S[IV] lifetimes (Guekezian et al., 1997). In our modeling, we therefore do not adopt the lifetime measure of Guekezian et al.…”

“…We conducted sensitivity tests where we adjusted T disp,0 = 10 days for n = 4, and found our conclusions to be unaffected. Similarly, our results are insensitive to the uncertainty in [S[IV]] 0 (Meyer et al, 1979(Meyer et al, , 1982, because this uncertainty only affects k disp,n when n > 1, for which disproportionation is subdominant to other processes like photolysis. We conclude that our results are insensitive to our approach to estimating T disp,0 .…”

“…We also considered the hypothesis that n < 0, which would explain the shorter S[IV] lifetime of Guekezian et al. (1997) ([ S [ IV ]] 0 = 0.01 M) compared to the results at higher [ S [ IV ]] 0 (Meyer et al., 1979, 1982; Petruševski et al., 2013) and would be an alternative explanation for the higher relative [S[IV]] loss in our 10 mM samples relative to our 100 mM samples. However, negative reaction kinetics are extremely rare, and are generally associated with heterogenous reactions (e.g., due to competition for a fixed supply of reaction sites on a catalyst); no such mechanism applies here.…”

“…Particularly highlighted in the literature is uncertainty regarding the rate of disproportionation of S[IV], which is proposed as the main loss mechanism (Halevy, 2013; Kasting et al., 1989). Literature estimates of the timescale of this process span >2 orders of magnitude (Guekezian et al., 1997; Meyer et al., 1979). In addition, there are other loss mechanisms for S[IV] such as photolysis (Fischer & Warneck, 1996) that are relevant to prebiotic conditions that have not been considered in estimating prebiotic S[IV] concentrations.…”

“…If S[IV] disproportionation is poorly constrained at high temperature, it is downright contradictory at low temperatures (Table 1). Most literature studies report non‐detections of S[IV] disproportionation at low temperatures, with lower limits on the room‐temperature lifetime of anoxic S[IV] solutions ranging from >4 months to ≥5 years (Cohen et al., 1982; Halevy et al., 2007; Meyer et al., 1979, 1982; Petruševski et al., 2013). On the other hand, Guekezian et al.…”