A Mesoarchean shift in uranium isotope systematics

Abstract

Oxygenic photosynthesis fundamentally transformed all major biogeochemical cycles and increased the size and complexity of Earth's biosphere. However, there is still debate about when this metabolism evolved. As oxygenic photosynthesis is the only significant source of O 2 at Earth's surface, O 2-sensitive trace element enrichments and isotopic signatures in Archean sedimentary rocks can potentially be used to determine the onset of oxygenic photosynthesis by tracking shifts in the oxidative capacity of Earth's surface environment. Here, we present an extensive new Archean U isotope record from iron formations, organic-rich shales, and paleosols. Variability in  238 U values gradually increased from Archean to Phanerozoic, consistent with current view of gradual oxidation of Earth's surface. In addition, statistical analysis on available  238 U data indicates a turning point of  238 U variability at roughly 3.0 billon years ago. We suggest that such a turning point in  238 U variability indicates the initiation of relatively large-scale oxidative weathering of U(IV)-bearing minerals, implying that oxygenic photosynthesis may have evolved before 3.0 billion years ago.

Early Archean origin of Photosystem II

“…In fact, even the scenario in which ΔT is a billion years (ν max = 5.03 ± 1.42) may be an overestimation and could potentially indicate that the age of the duplication event that led to D1 and D2 occurred immediately after the origin of the earliest reaction center. In consequence, the evolution of the core subunits of PSII is more consistent with a scenario in which oxygenic photosynthesis originated long before the GOE as supported by the geochemical record of inorganic redox proxies (Crowe et al, 2013;Havig, Hamilton, Bachan, & Kump, 2017;Planavsky et al, 2014;Wang et al, 2018).…”

“…Our present finding that the duplication leading to L and M occurred significantly later in anoxygenic Type II reaction centers opens the possibility that oxygen could have also been a driving force in their heterodimerization process, since K would have encountered these selection pressures at a time when oxygen concentrations began to rise or fluctuate in localized environments during the late Archean (Bosak, Liang, Sim, & Petroff, ; Lyons, Reinhard, & Planavsky, ; Riding, Fralick, & Liang, ; Wang et al., ). Mirroring the evolution of Type II reaction centers, a molecular clock study on Type I reaction centers showed that the duplication event that led to the heterodimerization of the core of Photosystem I was also more likely to be the oldest node after the root (Cardona et al., ).…”

“…For comparison, a calibration of 2.7 Ga was also used (Calibration 2) to test the effect on the estimated divergence times of an older age for crown group Cyanobacteria. Geological evidence suggests that oxygen “whiffs” or “oases” could significantly predating the GOE (Havig et al., ; Lyons et al., ; Planavsky et al., ; Wang et al., ) so this scenario is not entirely implausible.…”

“…For comparison, a calibration of 2.7 Ga was also used (Calibration 2) to test the effect on the estimated divergence times of an older age for crown group Cyanobacteria. Geological evidence suggests that oxygen "whiffs" or "oases" could significantly predating the GOE (Havig et al, 2017;Lyons et al, 2014;Planavsky et al, 2014;Wang et al, 2018) so this scenario is not entirely implausible. The calibration points on D1 were allocated on Group 4 because this type of D1 is the only one retained in all Cyanobacteria with PSII, it is the only type of D1 inherited by photosynthetic eukaryotes, and it is the main D1 used to catalyze water oxidation under most growth conditions: see Cardona et al (2015) for a detailed analysis of the evolution of D1 proteins.…”

Evolution of cellular metabolism and the rise of a globally productive biosphere

“…from fossils, biomarkers or other geochemical proxies) imposed on the calculations [215][216][217][268][269][270][271][272][273]. A range of genomic and geochemical evidence nevertheless suggests that the roots of cyanobacteria and the initiation of atmospheric oxygenation pre-date the Great Oxidation Event by several hundred million years [268,271,[273][274][275][276][277][278][279][280][281]. Similarly, paleontological evidence and molecular clock estimates generally agree the roots of eukaryotic photosynthesis pre-date the Neoproterozoic Oxidation Event by at least several hundred million years [215][216][217]269,272].…”