Mercury abundance and isotopic composition indicate subaerial volcanism prior to the end-Archean “whiff” of oxygen

Abstract

Earth’s early atmosphere witnessed multiple transient episodes of oxygenation before the Great Oxidation Event 2.4 billion years ago (Ga) [e.g., A. D. Anbar et al., Science 317, 1903–1906 (2007); M. C. Koehler, R. Buick, M. E. Barley, Precambrian Res. 320, 281–290 (2019)], but the triggers for these short-lived events are so far unknown. Here, we use mercury (Hg) abundance and stable isotope composition to investigate atmospheric evolution and its driving mechanisms across the well-studied “whiff” of O2 recorded in the ∼2.5-Ga Mt. McRae Shale from the Pilbara Craton in Western Australia [A. D. Anbar et al., Science 317, 1903–1906 (2007)]. Our data from the oxygenated interval show strong Hg enrichment paired with slightly negative ∆199Hg and near-zero ∆200Hg, suggestive of increased oxidative weathering. In contrast, slightly older beds, which were evidently deposited under an anoxic atmosphere in ferruginous waters [C. T. Reinhard, R. Raiswell, C. Scott, A. D. Anbar, T. W. Lyons, Science 326, 713–716 (2009)], show Hg enrichment coupled with positive ∆199Hg and slightly negative ∆200Hg values. This pattern is consistent with photochemical reactions associated with subaerial volcanism under intense UV radiation. Our results therefore suggest that the whiff of O2 was preceded by subaerial volcanism. The transient interval of O2 accumulation may thus have been triggered by diminished volcanic O2 sinks, followed by enhanced nutrient supply to the ocean from weathering of volcanic rocks causing increased biological productivity.

Reexamination of 2.5-Ga “whiff” of oxygen interval points to anoxic ocean before GOE

“…The ABDP-9 drill core, which was drilled by the NASA Astrobiology Drilling Program in 2004, contains a complete section of the Mount McRae Shale (105.13 to 190.08 m). It has been heavily sampled and analyzed with an array of elemental abundance and isotopic redox tracers focused on trace elements, sulfur, and iron (3,(16)(17)(18)(19)(20)(21)(22)(23)(24)32).…”

“…The ABDP-9 drill core, which was drilled by the NASA Astrobiology Drilling Program in 2004, contains a complete section of the Mount McRae Shale (105.13 to 190.08 m). It has been heavily sampled and analyzed with an array of elemental abundance and isotopic redox tracers focused on trace elements, sulfur, and iron ( 3 , 16 – 24 , 32 ). Analyses of this carbonaceous black shale are often interpreted to record a “whiff” of oxygen from ∼153- to 125-m core depth, a transient appearance of O 2 ( Fig.…”

“…One of the first sedimentary records proposed to document trace levels of local oxygen before the global GOE is the heavily studied ∼2.5-Ga Mount McRae Shale (3,16). In a multifaceted argument developed over the past decade, several different lines of evidence have been brought to bear (3,(16)(17)(18)(19)(20)(21)(22)(23)(24). For example, Anbar et al (3) identified a ∼28-m section of shale with high Mo content, correlating roughly with enrichments in total organic carbon (TOC) and Re, which was not seen in the overlying shales or in a lower shale unit (Fig.…”

Dissipative Photochemical Abiogenesis of the Purines

“…We have identified the long wavelength part of the UV-C region (∼210–285 nm), plus part of the UV-B and UV-A regions (∼310–360 nm), of the solar spectrum as the thermodynamic potential which could have driven the molecular dissipative structuring [ 21 , 26 ], proliferation, and evolution relevant to the origin of life. This light prevailed at Earth’s surface from the Hadean, before the origin of life (somewhere near the beginning of the Archean ∼3.9 Ga), and for perhaps as long as 1400 million years until the formation of an ozone layer at about 2.5 Ga [ 29 , 31 , 32 ] after natural oxygen sinks (e.g., volcanic reducing gases such as CH , CO, H 2 S and Fe ) became overwhelmed by organisms performing oxygenic photosynthesis, possibly fertilized by volcanic phosphorus [ 33 ].…”

The Dissipative Photochemical Origin of Life: UVC Abiogenisis of the Purines

“…We have identified the long wavelength part of the UVC region (∼ 210-285 nm), plus the long wavelength part of the UVB and short wavelength part of the UVA regions (∼ 310-360 nm), of the solar spectrum as the thermodynamic potential which could have driven the molecular dissipative structuring [21,26], proliferation, and evolution relevant to the origin of life. This light prevailed at Earth's surface from the Hadean, before the origin of life (soemwhere near the beginning of the Archean ∼ 3.9 Ga), and for perhaps as long as 1600 million years [29][30][31] until the formation of an ozone layer at about 2.5 Ga after natural oxygen sinks (e.g., volcanic reducing gases such as CO or H 2 S and Fe +2 ) became overwhelmed by organisms performing oxygenic photosynthesis, perhpas fertilized by volcanic phosphorus [32].…”