Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Abstract

The oxygen content of Earth's atmosphere has varied greatly through time, progressing from exceptionally low levels before about 2.3 billion years ago, to much higher levels afterward. In the absence of better information, we usually view the progress in Earth's oxygenation as a series of steps followed by periods of relative stasis. In contrast to this view, and as reported here, a dynamic evolution of Earth's oxygenation is recorded in ancient sediments from the Republic of Gabon from between about 2,150 and 2,080 million years ago. The oldest sediments in this sequence were deposited in well-oxygenated deep waters whereas the youngest were deposited in euxinic waters, which were globally extensive. These fluctuations in oxygenation were likely driven by the comings and goings of the Lomagundi carbon isotope excursion, the longest-lived positive δ 13 C excursion in Earth history, generating a huge oxygen source to the atmosphere. As the Lomagundi event waned, the oxygen source became a net oxygen sink as Lomagundi organic matter became oxidized, driving oxygen to low levels; this state may have persisted for 200 million years.GOE | Paleoproterozoic | marine chemistry | Mo isotope | trace metal

Spatial and temporal trends in Precambrian nitrogen cycling: A Mesoproterozoic offshore nitrate minimum

“…1 shows a compilation of bulk nitrogen isotopic compositions from offshore marine environments, highlighting the decline between ~1.7 Ga and ~1.2 Ga or possibly later. This interval post-dates the proposed mid-Paleoproterozoic oxygen overshoot (~2.3-2.0 Ga, Bekker and Holland, 2012;Canfield et al, 2013;Partin et al, 2013;Hardisty et al, 2014) and has recently been identified as a time when atmospheric pO 2 may have dropped back to as little as 0.1% or as great as 4% (Zhang et al, 2016;Cox et al, 2016) of present atmospheric levels until a second, potentially protracted rise to nearer modern amounts across the Neoproterozoic/Paleozoic, possibly beginning at ~800 Ma Blamey et al, 2016). Statistical analysis of global Fe-speciation data indicates that while subsurface anoxia was widespread throughout the Proterozoic Eon, euxinia was disproportionately common in Mesoproterozoic oceans (Sperling et al, 2015), consistent with lower atmospheric oxygen levels.…”

Oxygen requirements of the earliest animals

“…Indeed, oxygen levels this high may have been reached as early as the Great Oxidation Event some 2.3-2.4 billion years ago (43,45) and may have persisted at these levels through much of the intervening time (43,44), with some likely swings to lower levels, however, around 1.8 billion years ago (46). Oxygen levels supportive of sponges may have been met even earlier, at least locally, in Archean oxygen oases (47).…”

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

“…Given that the oxygen content of the oceans directly controls seawater U concentrations once oxidative continental weathering was established, the observed decrease could be due to a subsequent drop in the level of atmospheric and seawater oxygen following the Lomagundi event. It seems plausible that net organic carbon burial associated with oxygen production during the Lomagundi event later became an oxygen sink as organic matter became oxidised, driving oxygen to low levels that may have persisted for some hundreds of million years thereafter (Bekker and Holland, 2012;Canfield et al, 2013).…”