Environmental niches and metabolic diversity in Neoarchean lakes

Abstract

The diversification of macro-organisms over the last 500 million years often coincided with the development of new environmental niches. Microbial diversification over the last 4 billion years likely followed similar patterns. However, linkages between environmental settings and microbial ecology have so far not been described from the ancient rock record. In this study, we investigated carbon, nitrogen, and molybdenum isotopes, and iron speciation in five non-marine stratigraphic units of the Neoarchean Fortescue Group, Western Australia, that are similar in age (2.78-2.72 Ga) but differ in their hydro-geologic setting. Our data suggest that the felsic-dominated and hydrologically open lakes of the Bellary and Hardey formations were probably dominated by methanogenesis (δ C = -38.7 ± 4.2‰) and biologic N fixation (δ N =-0.6 ± 1.0‰), whereas the Mt. Roe, Tumbiana and Kylena Formations, with more mafic siliciclastic sediments, preserve evidence of methanotrophy (δ C as low as -57.4‰, δ C as low as -9.2‰) and NH loss under alkaline conditions. Evidence of oxygenic photosynthesis is recorded only in the closed evaporitic Tumbiana lakes marked by abundant stromatolites, limited evidence of Fe and S cycling, fractionated Mo isotopes (δ Mo = +0.4 ± 0.4‰), and the widest range in δ C (-57‰ to -15‰), suggesting oxidative processes and multiple carbon fixation pathways. Methanotrophy in the three mafic settings was probably coupled to a combination of oxidants, including O and SO . Overall, our results may indicate that early microbial evolution on the Precambrian Earth was in part influenced by geological parameters. We speculate that expanding habitats, such as those linked to continental growth, may have been an important factor in the evolution of life.

The Archean atmosphere

“…Then, by 2.8 to 2.6 Ga ago, increasing concentrations and isotopic fractionation of Mo and S in marine shales suggest that O 2 proximal to cyanobacterial mats and stromatolites on land oxidized sulfides and boosted sulfate and Mo riverine fluxes to the oceans (70,80,(102)(103)(104). These trends are consistent with isotopic evidence for Neoarchean methanotrophy and oxidative nitrogen cycling (105)(106)(107)(108)(109).…”

Microbially influenced formation of Neoarchean ooids

“…A bulk δ 13 C carb value of −1.2‰ obtained from the oolite is slightly more depleted in 13 C relative to the average obtained for Tumbiana Formation carbonate rocks sampled in outcrop (−0.7‰, Coffey, Flannery, Walter, & George, ). Bulk δ 13 C org values (Table ) averaging ~−44.1‰ are comparable to values obtained for stromatolites, other sedimentary carbonates, and organic‐rich shales within the formation (Coffey et al., ; Eigenbrode & Freeman, ; Flannery et al., ; Slotznick & Fischer, ; Stüeken et al., ; Thomazo, Ader, Farquhar, & Philippot, ; Thomazo, Ader, & Philippot, ). The samples are organic‐lean (TOC = <0.07%).…”

Environmental control on microbial diversification and methane production in the Mesoarchean

“…Differences between marine and non-marine ecosystems have been inferred from the Neoarchean rock record (2.8-2.5 Ga), where shallow marine and non-marine facies show markedly more negative organic carbon isotope values than open-ocean sediments, which has been interpreted as evidence of higher oxygen availability and methanotrophy in continental settings (Eigenbrode and Freeman, 2006;Flannery et al, 2016). For the Neoarchean, this interpretation is consistent with increasing evidence for temporary and/or localized appearances of free O 2 in surface environments at this time (Anbar et al, 2007;Kendall et al, 2010;Siebert et al, 2005;Stüeken et al, 2017;Wille et al, 2007). In the Mesoarchean, however, evidence of biological O 2 production is scarce (Crowe et al, 2013;Homann et al, 2015;Planavsky et al, 2014;Riding et al, 2014;Stüeken et al, 2012).…”