Evidence for oxygenic photosynthesis half a billion years before the Great Oxidation Event

Abstract

Method Summary:Rocks were collected from either drill core or surface outcrop without obvious weathering. Exterior surfaces were removed. Samples were powdered in a tungsten carbide mill from chips that were picked to avoid veins. Major element concentrations were determined using either an ICP-MS (Agilent 7500ce Series, or Thermo Element2) or an ICP-AES (Iris Advantage) after a three-acid dissolution or a metaborate fusion, respectively. Accuracy and precision for major element analyses was based on duplicates of the geostandards IF-G, SDO-1, and BHVO-1, and estimated error is less than 5%. For Mo isotopes, powdered samples were digested with concentrated HNO 3 + HF and HNO 3 + HCl, and then the samples were evaporated and dissolved with 7 mol/L HCl.

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…This pattern is also observed in the IF of the 2.95 Ga Sinqeni Formation, Pongola Supergroup, where the Mo isotope signature is consistent with the interaction with Mn(IV) oxides (Planavsky et al, 2014a). These Mo isotope signatures likely required an oxygenated water column and delivery of Mn(IV) oxides to the sediment pile, given rapid Mn(IV) oxide reduction via Fe 2+ (e.g., Busigny et al, 2014).…”

The evolution of Earth's biogeochemical nitrogen cycle

“…1, Godfrey and Glass, 2011). Even though Mo isotopes indicate that some dissolved Mo was present in seawater back to 3.0 Gyr, possibly sourced from mild oxidative weathering or hydrothermal inputs (McManus et al, 2002;Planavsky et al, 2014a), dissolved Mo concentrations in the Precambrian ocean may have been as low as 1-10 nM compared to 100 nM today (Anbar, 2008;Reinhard et al, 2013b;Scott et al, 2008). This raises the question of whether one or both of these enzymes were Mo-limited during early evolution (Anbar and Knoll, 2002).…”

“…However, molecular phylogenies suggest that Anf and Vnf are in fact more recent inventions, because they are only found in very few organisms that also possess and preferentially produce Nif (Boyd and Peters, 2013;McGlynn et al, 2012). Furthermore, Mo isotope data from 3.0 Gyr iron formations suggest appreciable levels of mobile molybdate ions in seawater (Planavsky et al, 2014a). Sufficient molybdenum concentrations in seawater could have been sustained by either localized oxidative weathering (Crowe et al, 2013;Guy et al, 2012;Planavsky et al, 2014a) or by low-temperature hydrothermal fluids which may contribute ~10% of the Mo flux into the modern ocean (McManus et al, 2002).…”

“…Furthermore, Mo isotope data from 3.0 Gyr iron formations suggest appreciable levels of mobile molybdate ions in seawater (Planavsky et al, 2014a). Sufficient molybdenum concentrations in seawater could have been sustained by either localized oxidative weathering (Crowe et al, 2013;Guy et al, 2012;Planavsky et al, 2014a) or by low-temperature hydrothermal fluids which may contribute ~10% of the Mo flux into the modern ocean (McManus et al, 2002).…”

“…The oldest possible signs of oxygenic photosynthesis date back to 3.8 Gyr (reviewed in Buick, 2008). Recent work proposes a minimum age of 3.0 Gyr (Crowe et al, 2013;Planavsky et al, 2014a). However, prior to ~2.3 Gyr, atmospheric O 2 did likely not accumulate to more than 10 -5 times present atmospheric levels (PAL), i.e.…”