Atmospheric oxygenation three billion years ago

Abstract

It is widely assumed that atmospheric oxygen concentrations remained persistently low (less than 10(-5) times present levels) for about the first 2 billion years of Earth's history. The first long-term oxygenation of the atmosphere is thought to have taken place around 2.3 billion years ago, during the Great Oxidation Event. Geochemical indications of transient atmospheric oxygenation, however, date back to 2.6-2.7 billion years ago. Here we examine the distribution of chromium isotopes and redox-sensitive metals in the approximately 3-billion-year-old Nsuze palaeosol and in the near-contemporaneous Ijzermyn iron formation from the Pongola Supergroup, South Africa. We find extensive mobilization of redox-sensitive elements through oxidative weathering. Furthermore, using our data we compute a best minimum estimate for atmospheric oxygen concentrations at that time of 3 × 10(-4) times present levels. Overall, our findings suggest that there were appreciable levels of atmospheric oxygen about 3 billion years ago, more than 600 million years before the Great Oxidation Event and some 300-400 million years earlier than previous indications for Earth surface oxygenation.

Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

“…Pavlov and Kasting, 2002). Contrasting studies, however, report the enrichment of redox sensitive metals as well as redox-related changes in their stable isotopic composition (such as Mo or Cr; e.g., Anbar et al, 2007;Frei et al, 2009;Crowe et al, 2013) suggesting an early onset of oxidative continental weathering, notably the presence of atmospheric oxygen some 50-100 or probably as early as 600 million years prior to the GOE.…”

The evolution of Earth's biogeochemical nitrogen cycle

“…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 threshold for mass-independent fractionation (MIF) in sulfur isotopes (Pavlov and Kasting, 2002), and it may even have been significantly lower (Kurzweil et al, 2013). Before 2.75 Ga, oxidative weathering is thought to have been trivial on a global scale (Stüeken et al, 2012) and, if present, restricted to local areas where cyanobacteria may have been thriving (Crowe et al, 2013;Lalonde and Konhauser, 2015). There are no documented occurrences of euxinia in the Paleo-and Meso-Archean, suggesting that marine sulfate concentrations were very low, possibly <0.2 mM (Habicht 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.…”

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

“…This implies that these signatures cannot be easily linked to anoxygenic photosynthetic Mn(II) oxidation more than a half of billion years before the GOE. Similarly, Cr isotopes from the 2.98 Ga Nsuze paleosol, also in the Pongola Supergroup, have been used as evidence for significant oxidative weathering on land, and thus appreciable levels of atmospheric oxygen, even at that time (Crowe et al, 2013). Frei et al (2016) combined U/Th ratios and Cr isotopes to argue for oxidative weathering as far back in time as the 3.8-3.7 Ga Isua Supracrustal Belt, but at very low atmosphere oxygen contents (i.e., <<10 -5 present atmospheric levels, PAL; Fig.…”