Sulfur and mercury MIF suggest volcanic contributions to Earth’s atmosphere at 2.7 Ga

Abstract

The Archean eon is associated with large-scale changes in Earth's geosphere and biosphere, including the onset of plate tectonics and the expansion of oxygenic photosynthesis, although the full impacts of these changes on the atmosphere remain unclear. Here we present coupled records of mass independent fractionation of sulfur (S-MIF) and mercury (Hg-MIF) isotopes from well preserved sediments of the ∼2.7 billion year old (Ga) Manjeri Formation, Belingwe Greenstone Belt, Zimbabwe. These palaeoatmospheric proxies record different trends for S-MIF and odd number Hg-MIF versus even number Hg-MIF, providing novel constraints on atmospheric chemistry during this time. S-MIF and odd number Hg-MIF values are muted in comparison to values preserved in later Archean sediments, representing a combination of enhanced volcanic input and local mixing. Even number Hg-MIF is absent from these sediments, consistent with complete photo-oxidation of gaseous Hg 0 , which could have been driven by increased halogen emissions from arc volcanism. When considered within a global geodynamic context, these MIF data suggest an important role for subduction zone-related volcanism associated with early plate tectonics in modulating the ∼2.7 Ga atmosphere.

Secular Evolution of Continents and the Earth System

“…Recent work suggests the GOE may be a protracted transition that extended over 10s to 100s of millions of years (Hodgskiss & Sperling, 2021; Ostrander et al., 2021). Thus, the drivers of the GOE likely commenced in the late Archean and included subaerial exposure of the cratons and widespread mafic magmatism, with associated extensive degassing (including volcanic H 2 O, CO 2 , N 2 , and SO 2 ) and weathering (Ciborowski & Kerr, 2016; Hodgskiss & Sperling, 2021; Marty et al., 2019; Meixnerová et al., 2021; Zerkle et al., 2021). In turn, these events would have increased nutrient supply to the oceans and enhanced biological activity (Cox et al., 2018; Hao et al., 2020).…”

Multiple sulphur isotope record of Paleoarchean sedimentary rocks across the Onverwacht Group, Barberton Greenstone Belt, South Africa

“…Rather, we suggest that moderate‐to‐small MIF‐S signatures are more typical of the Paleoarchean era in contrast to large MIF‐S signals (up to c. 12‰) found in the Neoarchean and that previously reported large MIF‐S from the Paleoarchean need to be further reviewed. In comparison to the so called “mid‐Archean MIF minimum” that shows subdued MIF signatures in the Mesoarchean (e.g., Zerkle et al, 2021 and references therein), our Paleoarchean data exhibit greater variability. This has been attributed variously to changes in global atmospheric chemistry, which could dampen MIF‐S production (Domagal‐Goldman et al, 2008; Farquhar et al, 2007; Kurzweil et al, 2013; Liu et al, 2019) or to dilution and/or mixing of atmospheric sulphur sources on a local or regional scale (Guy et al, 2012; Marin‐Carbonne et al, 2014; Thomazo et al, 2013; Zerkle et al, 2021).…”

“…In comparison to the so called “mid‐Archean MIF minimum” that shows subdued MIF signatures in the Mesoarchean (e.g., Zerkle et al, 2021 and references therein), our Paleoarchean data exhibit greater variability. This has been attributed variously to changes in global atmospheric chemistry, which could dampen MIF‐S production (Domagal‐Goldman et al, 2008; Farquhar et al, 2007; Kurzweil et al, 2013; Liu et al, 2019) or to dilution and/or mixing of atmospheric sulphur sources on a local or regional scale (Guy et al, 2012; Marin‐Carbonne et al, 2014; Thomazo et al, 2013; Zerkle et al, 2021). In addition, we suggest that some of this difference may be due to comparing predominantly SIMS data that show greatest intra‐sample variability from the Paleoarchean to a record largely comprising bulk S‐isotope data from the Mesoarchean.…”

“…Indeed, subsequent studies of the Dresser Formation by Ueno et al (2008) have found that the barite hosted pyrites contain small negative Δ 33 S values, in contrast to the seven grains of Ni-bearing sulphides with positive Δ 33 S measured by Philippot et al (2007) that constitute a very rare and only minor fraction of the Dresser Formation sulphides (see also Shen et al, 2009). We conclude that the rocks of the (Domagal-Goldman et al, 2008;Farquhar et al, 2007;Kurzweil et al, 2013;Liu et al, 2019) or to dilution and/or mixing of atmospheric sulphur sources on a local or regional scale (Guy et al, 2012;Marin-Carbonne et al, 2014;Thomazo et al, 2013;Zerkle et al, 2021). In addition, we suggest that some of this difference may be due to comparing predominantly SIMS data that show greatest intra-sample variability from the Paleoarchean to a record largely comprising bulk S-isotope data from the Mesoarchean.…”

On the origin and evolution of microbial mercury methylation

“…Industrial mercury sources include fossil fuel combustion, mining, cement production and waste incineration (AMAP Assessment 2011); natural sources primarily involve geothermal activity. In fact, volcanos and hot springs have emitted mercury throughout geologic time since Earth's earliest geologic history (Grasby et al 2019;Zerkle et al 2020Zerkle et al , 2021. Following the widespread oxygenation of the early ~2.4 billion years ago, Hg II would therefore be commonly found as a trace metal in hydrothermal environments.…”