Great Oxidation Research Articles

Inspired oxygen: present, past, and future.

As earthlings, we take the oxygen in the air that we breathe for granted. Few people realize that this easy access to oxygen makes us unique in the whole universe. Nowhere else in our planetary system or in distant stars has stable oxygen ever been detected. However, the present plentiful supply of oxygen in our atmosphere was not always there. Long after the Earth was formed some 4.5 billion years ago, the Po2 in the atmosphere was near zero, and it remained so for millions of years. But about 2 billion years ago, the Po2 dramatically increased to as high as 200 mmHg during the Great Oxygen Event, due to the activity of microorganisms, the cyanobacteria. Subsequently, the oxygen level fell to the intermediate values that we have today. Here, we also look to the future, for example, the next 50 years. This period will be special because it will include the beginnings of human space exploration, initially to the Moon and Mars. Neither of these has atmospheric oxygen. Nevertheless, plans to visit and live on both of these are developing rapidly. We consider the fascinating problems of how to ensure that sufficient oxygen will be available for the groups of people. Although it is interesting to discuss these issues now, we can expect that major advances will be made in the next few years.

The origin and impeded dissemination of the DNA phosphorothioation system in prokaryotes

Phosphorothioate (PT) modification by the dnd gene cluster is the first identified DNA backbone modification and constitute an epigenetic system with multiple functions, including antioxidant ability, restriction modification, and virus resistance. Despite these advantages for hosting dnd systems, they are surprisingly distributed sporadically among contemporary prokaryotic genomes. To address this ecological paradox, we systematically investigate the occurrence and phylogeny of dnd systems, and they are suggested to have originated in ancient Cyanobacteria after the Great Oxygenation Event. Interestingly, the occurrence of dnd systems and prophages is significantly negatively correlated. Further, we experimentally confirm that PT modification activates the filamentous phage SW1 by altering the binding affinity of repressor and the transcription level of its encoding gene. Competition assays, concurrent epigenomic and transcriptomic sequencing subsequently show that PT modification affects the expression of a variety of metabolic genes, which reduces the competitive fitness of the marine bacterium Shewanella piezotolerans WP3. Our findings strongly suggest that a series of negative effects on microorganisms caused by dnd systems limit horizontal gene transfer, thus leading to their sporadic distribution. Overall, our study reveals putative evolutionary scenario of the dnd system and provides novel insights into the physiological and ecological influences of PT modification.

New geochronologic and geochemical constraints for the Pedro Pereira metavolcanosedimentary sequence: Evidence for a 2.77 Ga oxygen oasis record in the São Francisco-Congo paleocontinent

Exposed within the reworked basement of the Araçuaí orogen, eastern Brazil, the Pedro Pereira metavolcanosedimentary sequence (PPMS) comprises a lower unit dominated by metaultramafic/mafic rocks, an intermediate unit dominated by metarhyolites and a predominant upper unit of acid metavolcanites associated with chemical and clastic metasedimentary rocks. This sequence has been defined and investigated in the ’80s when it was considered as a Mesoarchean greenstone belt. Since then, few studies have addressed these rocks, and due to the lack of reliable geochronological data, a Paleoproterozoic age has also been suggested for the sequence. To reevaluate the age and evolution of the unit, new whole-rock geochemical and zircon U–Pb (LA-ICPMS) geochronologic data were obtained for the iron formation and acid metavolcanic rocks, respectively. When normalized to post-Archean Australian Shale standard, BIF samples can be divided into three groups. Group 1 BIF samples are marked by significant enrichment of the LREE, very high ∑REE + Y, positive La anomaly, extreme negative Ce anomaly, negative Eu anomaly, and subchondritic Y/Ho ratio. In contrast, Group 2 BIFs are marked by the enrichment of HREE, low ∑REE + Y, positive La anomaly, negative Eu anomaly, slight negative Ce anomaly, and predominantly super- and subchondritic Y/Ho ratios. The massive iron formation (MIF) group shows very high middle-to-heavy REE + Y enrichment, strong negative Ce anomaly, negative Eu anomaly, very high ∑REE + Y, and variable Y/Ho ratios. The modification of the iron formation by post-depositional hydrothermal alteration might have disturbed the original basin water signature. However, Group 2 is more compatible with pure chemical precipitates and its slight negative anomalies suggest an oxic environment. A PPMS metarhyolite from the upper portion of the sequence interlayered with the BIFs yielded the Concordia Age of 2771 ± 8.4 Ma. This age rules out a Paleoproterozoic origin for the PPMS, as suggested/considered by recent papers. The results imply that PPMS possibly represents one of the oldest records of oxygenation previous to the GOE in the geologic archives and could provide information to understand the early evolution of localized pockets of oxygen before the Great Oxidation Event.

Dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event

Compared with Phanerozoic strata, sulfate minerals are relatively rare in the Precambrian record; this is probably due to the lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals that are stratigraphically associated with the Ediacaran Shuram excursion (SE) – the largest negative δ 13 C excursion in Earth history. We evaluated 15 SE sections, all of which reveal the presence of sulfate minerals and/or enriched carbonate-associated sulfate concentrations, suggesting a rise in the sulfate reservoir. Notably, where data are available, the SE also reveals considerable enrichments in [Ba] relative to pre- and post-SE intervals. We propose that elevated seawater sulfate concentrations during the SE may have facilitated authigenesis of sulfate minerals. At the same time, the rise in Ba concentrations in shelf environments further facilitated barite deposition. A larger sulfate reservoir would stimulate microbial sulfate reduction and anaerobic oxidation of organic matter (including methane), contributing to the genesis of the SE. The existence of sulfate minerals throughout the SE suggests that oxidant pools were not depleted at that time, which challenges previous modelling results. Our study highlights the dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event. Supplementary material: SEM and EDS data and figures S1-S4 and tables S1-S3 are available at: https://doi.org/10.6084/m9.figshare.c.5602560 Thematic collection: This article is part of the ‘Sulfur in the Earth system’ collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system

A prolonged, two-step oxygenation of Earth's early atmosphere: Support from confidence intervals

Abstract The Great Oxidation Event (GOE), among Earth's most transformative events, marked the sustained presence of oxygen above 10−5 times the present atmospheric level. Estimates of the onset of the GOE span 2501–2225 Ma and are based primarily on the loss of mass-independent fractionation of sulfur isotopes (MIF-S) in pyrite. To better constrain the timing of the GOE, we apply probabilistic techniques to estimate the confidence intervals of four proxies: MIF-S, redox-sensitive detrital minerals, “red beds,” and I/(Ca + Mg). These GOE proxies are drawn from a highly fragmentary geologic record, and consequently, estimates of the 95% confidence intervals span tens to hundreds of millions of years—orders of magnitude larger than suggested by radiometric constraints on individual successions. Confidence interval results suggest that red beds and nonzero I/(Ca + Mg) values may have appeared earlier than 2480 Ma and 2460 Ma, respectively, whereas redox-sensitive detrital minerals and MIF-S may have disappeared after 2210 Ma and 2190 Ma, respectively. These data suggest a delay of potentially >300 m.y. between initial and permanent oxygenation of the atmosphere and a delay of tens of millions of years between onset of the Lomagundi-Jatuli carbon isotope excursion and permanent oxygenation of the atmosphere.

Significance of 56Fe depletions in late-Archean shales and pyrite

Sedimentary rocks and minerals formed during the final two-hundred million years of the Archean Eon (2.7 to 2.5 billion years ago, or Ga) are more depleted in 56Fe than at any other time in Earth’s past. Three hypotheses are proposed to explain these 56Fe depletions: (1) a very negative late-Archean seawater δ56Fe value, (2) “shuttling” of isotopically light Fe across the chemocline in redox-stratified settings, and (3) pyrite formation in an Fe(II)-rich ocean. Each of these scenarios has different implications for the initial oxidation of Earth’s surface, the climax of which – the Great Oxidation Event – immediately post-dates the appearance of these 56Fe depletions in the rock record. To help inform this debate, we measured the Fe isotope ratios of 120 shale and pyrite samples from Western Australia (Mt. McRae Shale and Jeerinah Formation) and South Africa (Klein Naute Formation) deposited between ∼2.65 Ga and ∼2.50 Ga. As in previous studies, we also find very strong sedimentary 56Fe depletions, to as low as δ56Fe = −2.06 ± 0.08‰ in bulk shales and δ56Fe = −2.31 ± 0.08‰ in pyrite. Some, but not all, of the severest 56Fe depletions appear alongside evidence of an Fe shuttle and local pyrite formation. These processes need not be mutually exclusive, and some combination of them likely played a partial, probably faciliatory role in driving some strong 56Fe depletions in our dataset. Most interestingly, and with little exception, the severest 56Fe depletions appear in samples deposited farther from shore under H2S-rich and anoxic (“euxinic”) conditions. We find it difficult to explain this connection without invoking the persistent presence of a very negative global seawater δ56Fe value during the latest Archean, one that was most consistently captured in sediments formed in distal euxinic settings. In order to impart this isotopic effect on seawater, the global seawater Fe(II) reservoir needed to have been partially oxidized during at least the final few hundreds of millions of years leading up to the Great Oxidation Event. Our new data add support to the idea that Earth’s initial oxidation was a long and protracted process rather than a rapid event.

Biosignatures Associated with Organic Matter in Late Paleoproterozoic Stromatolitic Dolomite and Implications for Martian Carbonates.

The documentation of biosignatures in Precambrian rocks is an important requirement in the search for evidence of life on other ancient planetary surfaces. Three major kinds of biosignatures are crucially important: primary microbial sedimentary textures, diagenetic organomineral assemblages, and stable isotope compositions. This study presents new petrographic, mineralogical, and organic geochemical analyses of biosignatures in dolomitic stromatolites from the Pethei Group (N.W.T., Canada) and the Kasegalik Formation of the Belcher Group (Nunavut, Canada). Both are approximately contemporary late Paleoproterozoic stromatolite-bearing dolomitic units deposited after the Great Oxidation Event. Micro-Raman and optical microscopy are used to identify and characterize possible diagenetic biosignatures, which include close spatial association of diagenetic materials (such as ferric-ferrous oxide and anatase) with disseminated organic matter (OM), dolomitic groundmass textures, and mineralized balls. Many of these petrographic relationships point to the oxidation of OM either biotically or abiotically in association with iron reduction and chemically oscillating reactions. Oxidation of OM in these stromatolites is consistent with the widespread oxidation of biomass during the late Paleoproterozoic Shunga-Francevillian Event. Biosignatures identified in this study are also compared with possible carbonate outcrops on Mars, and thereby contribute a basis for comparison with potential biosignatures in ancient martian terrains. Similarities are drawn between the paleoenvironments of the studied units to the Isidis and Chryse planitia as locations for potential extraterrestrial dolomitic stromatolites.

CO2 and O2 oxidized 2.7 Ga micrometeorites in two stages suggesting a >32% CO2 atmosphere

It is widely accepted that atmospheric pO2 < 1 ppm before the Great Oxidation Event. Yet a recent study found fossil micrometeorites (MMs) containing the oxidized iron species wüstite (FeO) and magnetite (Fe3O4) formed 2.7 billion years ago (Ga). How these MMs became oxidized is uncertain. Abundant O2 in the upper atmosphere and iron oxidation by CO2 have been suggested. However, photochemical reactions cannot produce sufficient O2, and oxidation by CO2 can only produce FeO, each individually failing to explain the formation of Fe3O4-only MMs. Using an oxidation model of iron MMs including photochemistry, we show that a >32% CO2 Archean atmosphere and different entry angles can generate the Fe3O4-only and Fe-FeO mixed composition MMs that have been discovered. Oxidation happens in two stages: by CO2 under brief melting, then by O2. Our results challenge existing constraints on Earth’s atmospheric CO2 concentration at 2.7 Ga and support a warm Late Archean despite the ‘faint young Sun’.

Analysis dates emergence of photosynthesis

Photosynthesis may have evolved about half a billion years before oxygen became abundant in Earth’s atmosphere, a new study suggests ( Proc. R. Soc. B 2021, DOI: 10.1098/rspb.2021.0675 ). This discovery updates the timing of one of the most important events in the planet’s history. Photosynthetic plants and bacteria use sunlight, water, and carbon dioxide to fuel their metabolisms, producing oxygen along the way. The evolution of oxygen-generating photosynthesis “is probably the single most important event that ever occurred on Earth, aside from the origin of life itself,” says Gregory Fournier, a geobiologist at the Massachusetts Institute of Technology who led the work. Scientists agree that photosynthesis evolved in microbes called cyanobacteria , but it’s not clear when. Studies suggest that photosynthesis evolved 500 million–1 billion years before the Great Oxygenation Event (GOE), which occurred about 2.4 billion years ago, when cyanobacteria drove a sharp increase in O 2 in

A global magnetotelluric graphite type locality: Multi-decade, multi-scale studies of the Eyre Peninsula anomaly

A major electrically conducting crustal structure has been imaged since the 1980 s using widely-spaced long-period magnetotelluric (MT) and geomagnetic depth sounding (GDS) sites across the Archean to Paleoproterozoic Eyre Peninsula, South Australia. The structure extends from the southern continental margin, trending SW-NE for at least 300 km. To constrain depth and lateral extent of the anomaly a transect of 39 broadband MT sites were collected with ∼ 2 km separation across lower Eyre Peninsula. Two-dimensional inversion images a low-resistivity conductor at depth 2–10 km, 20 km wide and dipping ∼ 10° to the east, spatially correlated with a topographic high. The conductor is bound on the eastern margin by the transpressional Kalinjala Shear Zone along the Paleoproterozoic Donington Suite, and on the western margin by the Archean Sleaford Complex. The low resistivity structure, with conductance of 20,000 S occurs in Paleoproterozoic carbonaceous marine sediments of the Darke Peak and Cleve groups that were thickened to amphibolite-grade metamorphic depths of at least 15 km and 550 ⁰C during the Kimban Orogeny (1730–1690 Ma), converting carbon to flake graphite in metapelites. Tight folding and exhumation of amphibolite-grade metapelites during the Kimban Orogeny, and dextral strain along the Kalinjala Shear Zone resulted in a laterally continuous electrical crustal conductor which outcrops as economic-grade graphite deposits adjacent to Kalinjala Shear Zone mylonites. In addition, a ∼ 40 km wide lower crustal conductor of integrated conductance 2000 S is imaged west from the Kalinjala Shear Zone. This lower crustal conductor may also be graphitic and represents deeply buried metapelites that have not been exhumed. We argue that the Paleoproterozoic Eyre Peninsula Anomaly results from graphitisation of sediments with significantly enhanced amount of organic carbon compared to any other time in Earth’s history, during the ∼ 2 Ga Lomagundi–Jatuli Event, which is associated with the great oxidation event.

The Bastar Craton of Central India: Tectonostratigraphic evolution and implications in global correlations

The Bastar Craton occupies a key position in the Peninsular India, being located between three cratonic nuclei of India, the Dharwar Craton in the southwest, the Singhbhum Craton in the northeast, and the Bundelkhand Craton in the northwest. The southeastern and the northern margins of the craton are bordered by the Proterozoic orogenic belts constituting the Eastern Ghats Mobile Belt and the Central Indian Tectonic Zone (the Satpura Mobile Belt), respectively. Analysis of the tectonostratigraphic evolution of the craton indicates the formation of the craton during Paleoarchean Era (~3582 Ma). The Archean evolution of the craton is marked by the development of granite-greenstone belts containing chemogenic sediments (Banded Iron Formations) and gold mineralisation . High-grade gneisses and granulites were developed during three orogenic episodes in the terrane (~2700 Ma Bailadila orogeny , ~2900 Ma Bengpal orogeny and ~3400 Ma Sukma orogeny). The Paleoproterozoic evolution of the craton is gleaned from the record of siliciclastic, volcaniclastics and chemogenic precipitates (carbonates, Banded Manganese Formation, and Banded Iron Formation) on the northern margin of the craton, which were deposited during the Great Oxidation Event (GOE; 2500–2300 Ma) and Paleoproterozoic glaciation (2400–2300 Ma) as well as immediately after the GOE (2050–1850 Ma). Effects of orogenic activities in the adjacent mobile belts are marked by the metamorphic and magmatic activities affecting the rocks at the margin of the craton. The Satpura orogenic event on the northern margin of the craton led to the amalgamation of the Bastar Craton with the Bundelkhand Craton at ~2250 and ~2100 Ma, forming the major part of the Peninsular India. Orogenic collapse (extension) developed basins transverse to the orogenic trend, where clastic, volcaniclastic and chemogenic sediments (Khairagarh and Chilpi Groups) were deposited. The southeastern margin of the craton has records of migmatisation and granite emplacement during the Eastern Ghats orogeny at ~1700 Ma. A number of sedimentary basins , aligned along a line parallel to the Eastern Ghats Mobile Belt, were developed during the orogenic collapse of the Eastern Ghats. Later orogenic activities along the Eastern Ghats were responsible for the development of depositional hiatus/unconformity within these sedimentary basins of the craton. Mafic dykes of different generations (2400 Ma, 2100 Ma and 1890 Ma) cutting across the Archean basement complex provide suitable markers for paleomagnetic reconstructions of the craton. The Archean and early Paleoproterozoic rock assemblages and mineralisation patterns in the craton show a broad similarity with the Western Australian Craton, indicating near-neighbourhood positions of the two ancient cratonic blocks. Paleomagnetic studies have shown the separation of these two blocks at ~2000 Ma, with the development of a paleo-ocean which closed subsequently during the amalgamation of the Bastar Craton with the East Antarctic Shield to form the Eastern Ghats Mobile Belt in three phases at ~1700–1600 Ma, ~1050–950 Ma and ~500 Ma, with extensional phase between 1450 and 1100 Ma. The Bastar Craton preserves important clues regarding the evolution of the ocean and atmospheric conditions in the early Earth. • The Bastar and Yilgarn Cratons were juxtaposed at ~2400 Ma. • Bundelkhand-Pilbara Cratons collided with Bastar-Yilgarn Cratons at ~2000 Ma. • Satpura-Singhbhum-Capricorn Orogen developed at ~2000 Ma. • No collision/accretion took place along the CITZ after ~1800 Ma. • New tectonic model for 1950–1000 Ma is proposed for Bastar-Yilgarn Cratons.

Reconciling evidence of oxidative weathering and atmospheric anoxia on Archean Earth.

Evidence continues to emerge for the production and low-level accumulation of molecular oxygen (O2) at Earth’s surface before the Great Oxidation Event. Quantifying this early O2 has proven difficult. Here, we use the distribution and isotopic composition of molybdenum in the ancient sedimentary record to quantify Archean Mo cycling, which allows us to calculate lower limits for atmospheric O2 partial pressures (PO2) and O2 production fluxes during the Archean. We consider two end-member scenarios. First, if O2 was evenly distributed throughout the atmosphere, then PO2 > 10–6.9 present atmospheric level was required for large periods of time during the Archean eon. Alternatively, if O2 accumulation was instead spatially restricted (e.g., occurring only near the sites of O2 production), then O2 production fluxes >0.01 Tmol O2/year were required. Archean O2 levels were vanishingly low according to our calculations but substantially above those predicted for an abiotic Earth system.

Mitochondria are responsible for reactive oxygen species damage in fish muscle

Ever since the Great Oxygenation Event approximately 2.4 billion years ago, when cyanobacteria flooded the atmosphere with oxygen, life has been in a Faustian pact with the colourless gas. Oxygen reacts with glucose in cells to produce the energy that powers life through a chain of events that culminates within the mitochondria. However, these reactions with the life-giving gas also produce a plethora of toxic by-products, known as reactive oxygen species, which can in turn damage DNA, proteins and lipids in cells. The question was whether the mitochondrial powerhouses are the main source of harmful oxygen toxins, or whether they are generated by other sources in the cell. ‘People have assumed that mitochondria are the main culprits in reactive oxygen species production, but Yufeng Zhang and Hoi Shan Wong challenged this notion in a Commentary in Journal of Experimental Biology in 2021’, says Stephen Kinsey from the University of North Carolina Wilmington, USA.Fortunately, Kinsey and graduate student Julie Neurohr (University of North Carolina Wilmington) knew of a unique tissue that could help to answer the question: fish muscle. ‘Fish red and white muscle is easily delineated and metabolically distinct’, says Kinsey, explaining that red muscle is packed with mitochondria and consumes large quantities of oxygen, while the larger white muscles are largely devoid of mitochondria and depend instead on anaerobic metabolism. By comparing the amount of damage caused by reactive oxygen species in the two tissues – and how both forms of muscle deal with the collateral damage – Kinsey and Neurohr might be able to begin unravelling whether mitochondria are the key culprits in the oxidative damage sustained by fish muscle.After fishing for pinfish (Lagodon rhomboides) in the Intracoastal Waterway at Wrightsville Beach, USA, Kinsey, Neurohr and Erik Paulson (University of North Carolina Wilmington) used an electron microscope to scrutinise both forms of muscle, revealing that the red muscle was packed with 7 times more mitochondria (comprising 6.9% of the muscle volume) than the white muscle (0.89% muscle volume). And when Neurohr checked the amount of damage caused by reactive oxygen species to DNA, proteins and lipids in both forms of muscle, the red muscle came out on top, suffering the most damage in all three categories, despite having higher levels of the reactive oxygen species neutralising proteins – superoxide dismutase and catalase – for protection. The red muscle with larger quantities of mitochondria seemed to be at most risk from the damage caused by reactive oxygen species produced by the cell's powerhouses.So, how do vulnerable red muscle cells deal with the increased risk of tissue damage caused by oxygen? Knowing that cells resort to two different forms of disposal – an engulfing system to clear up larger clusters of damaged proteins and a more targeted strategy, the ubiquitin–proteasome system, to dispose of individual unravelling proteins – the team checked for evidence of both and found that the red muscle was best prepared for mopping up individual damaged proteins. In contrast, the white muscle allows damaged proteins to form larger clumps before engulfing them.And, when Neurohr checked how quickly both forms of muscle produced new proteins, the red muscle was working at almost double the rate of the white muscle to replace the damaged proteins. ‘Together, these results suggest that higher mitochondrial content, which imparts the capacity for endurance in muscle, is associated with greater oxidative damage and cellular maintenance’, says Kinsey.

A critical review of molybdenum sequestration mechanisms under euxinic conditions: Implications for the precision of molybdenum paleoredox proxies

The observed difference in molybdenum (Mo) mobility and isotopic fractionation under oxic versus euxinic (i.e., anoxic and sulfidic) aqueous conditions provides a sound operational basis for the use of Mo geochemical signatures in ancient sedimentary records to infer palaeoceanographic redox conditions . While Mo is known to exist predominantly as molybdate (MoO 4 2− ) in oxic waters and convert into thiomolybdate species (MoO x S 4-x 2− ) under euxinic conditions, the pathways that lead to Mo sequestration are highly debated. As mechanistic understanding of Mo sequestration is crucial for accurately reconstructing the chemistry of ancient oceans and constraining the timing and intensity of oxygenation events through Earth's history using Mo paleoproxies, we have closely examined the current proposed mechanisms for Mo sequestration across a wide range of euxinic conditions. Through compilation and comparison of such information, we aim to provide an integrated view of Mo sequestration processes, to identify the current controversies as well as the roots of such controversies, and importantly, to propose avenues for future research. Sequestration of Mo may occur through complexation with organic matter (OM), reactions with oxyhydroxide and sulfide mineral surfaces, incorporation into iron sulfide crystal structures, formation of Mo-sulfide, and cellular assimilation. However, several major questions remains unresolved, including whether OM complexation plays a significant role in overall sedimentary Mo accumulation, whether the reduction of Mo(VI) occurs during interaction with Fe-S clusters/precipitates and/or with OM, whether microbial enzymatic reduction of Mo(VI) is important in Mo sequestration, whether synergistic effects exist between the biological and abiotic processes in Mo sequestration, and whether differences in reactivity among the various thiomolybdate intermediate species and tetrathiomolybdate influence the Mo sequestration process. At the end of the review, the reliability of Mo paleoproxies is discussed and reevaluated.

The Archean origin of oxygenic photosynthesis and extant cyanobacterial lineages.

The record of the coevolution of oxygenic phototrophs and the environment is preserved in three forms: genomes of modern organisms, diverse geochemical signals of surface oxidation and diagnostic Proterozoic microfossils. When calibrated by fossils, genomic data form the basis of molecular clock analyses. However, different interpretations of the geochemical record, fossil calibrations and evolutionary models produce a wide range of age estimates that are often conflicting. Here, we show that multiple interpretations of the cyanobacterial fossil record are consistent with an Archean origin of crown-group Cyanobacteria. We further show that incorporating relative dating information from horizontal gene transfers greatly improves the precision of these age estimates, by both providing a novel empirical criterion for selecting evolutionary models, and increasing the stringency of sampling of posterior age estimates. Independent of any geochemical evidence or hypotheses, these results support oxygenic photosynthesis evolving at least several hundred million years before the Great Oxygenation Event (GOE), a rapid diversification of major cyanobacterial lineages around the time of the GOE, and a post-Cryogenian origin of extant marine picocyanobacterial diversity.

Origin of cyanobacterial thylakoids via a non-vesicular glycolipid phase transition and their impact on the Great Oxygenation Event.

The appearance of oxygenic photosynthesis in cyanobacteria is a major event in evolution. It had an irreversible impact on the Earth, promoting the Great Oxygenation Event (GOE) ~2.4 billion years ago. Ancient cyanobacteria predating the GOE were Gloeobacter-type cells lacking thylakoids, which hosted photosystems in their cytoplasmic membrane. The driver of the GOE was proposed to be the transition from unicellular to filamentous cyanobacteria. However, the appearance of thylakoids expanded the photosynthetic surface to such an extent that it introduced a multiplier effect, which would be more coherent with an impact on the atmosphere. Primitive thylakoids self-organize as concentric parietal uninterrupted multilayers. There is no robust evidence for an origin of thylakoids via a vesicular-based scenario. This review reports studies supporting that hexagonal II-forming glucolipids and galactolipids at the periphery of the cytosolic membrane could be turned, within nanoseconds and without any external source of energy, into membrane multilayers. Comparison of lipid biosynthetic pathways shows that ancient cyanobacteria contained only one anionic lamellar-forming lipid, phosphatidylglycerol. The acquisition of sulfoquinovosyldiacylglycerol biosynthesis correlates with thylakoid emergence, possibly enabling sufficient provision of anionic lipids to trigger a hexagonal II-to-lamellar phase transition. With this non-vesicular lipid-phase transition, a framework is also available to re-examine the role of companion proteins in thylakoid biogenesis.

Origin, tectonic environment and age of the Bibole banded iron formations, northwestern Congo Craton, Cameroon: geochemical and geochronological constraints

AbstractThe newly discovered Bibole banded iron formations are located within the Nyong Group at the northwest of the Congo Craton in Cameroon. The Bibole banded iron formations comprise oxide (quartz-magnetite) and mixed oxide-silicate (chlorite-magnetite) facies banded iron formations, which are interbedded with felsic gneiss, phyllite and quartz-chlorite schist. Geochemical studies of the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations reveal that they are composed of &gt;95 wt % Fe2O3 plus SiO2 and have low concentrations of Al2O3, TiO2 and high field strength elements. This indicates that the Bibole banded iron formations were not significantly contaminated by detrital materials. Post-Archaean Australian Shale–normalized rare earth element and yttrium patterns are characterized by positive La and Y anomalies, a relative depletion of light rare earth elements compared to heavy rare earth elements and positive Eu anomalies (average of 1.86 and 1.15 for the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations, respectively), suggesting the influence of low-temperature hydrothermal fluids and seawater. The quartz-magnetite banded iron formations display true negative Ce anomalies, while the chlorite-magnetite banded iron formations lack Ce anomalies. Combined with their distinct Eu anomalies consistent with Algoma- and Superior-type banded iron formations, we suggest that the Bibole banded iron formations were deposited under oxic to suboxic conditions in an extensional basin. SIMS U–Pb data indicate that the Bibole banded iron formations were deposited at 2466 Ma and experienced metamorphism and metasomatism at 2078 Ma during the Eburnean/Trans-Amazonian orogeny. Overall, these findings suggest that the studied banded iron formations probably marked the onset of the rise of atmospheric oxygen, also known as the Great Oxidation Event in the Congo Craton.

Electrochemistry and the Development of the Hydrogen Fuel Cell [History

Sustainable life on Earth could not exist without breathable air or molecular oxygen, which makes up 21% of the atmosphere we breathe today. Oxygen did not always exist in the atmosphere, and it is believed that it evolved in a period in Earth's history around 2.33 billion years ago, known as the Great Oxygenation Event (GOE). Prior to this time, in the first 2 billion years since Earth was formed, oxygen was not present in the atmosphere. Earth's atmosphere was initially extremely hot, composed of about 75% hydrogen and 25% helium, which was identical to the atmosphere of most stars. In fact, hydrogen is the most common element in the universe today, composed of 90% of all matter, but being the lightest in weight of all gases, when the Earth cooled, it almost completely drifted off into space. A study regarding the GOE was published in the journal Nature Geo-science by research scientists from the School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, on 1 July 2019. In addressing the future need for sustainable green hydrogen economies worldwide, it is expected that only green methods of producing hydrogen, utilizing renewable energy sources, e.g., from wind and solar energy, will provide the mass production needs for all of these forms of transportation. One process utilized to produce the bulk of hydrogen worldwide uses steam reformation of natural gas. The natural gas is reacted with high-temperature steam to produce hydrogen, carbon monoxide, and a small amount of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The carbon monoxide is further reacted with water to provide extra amounts of hydrogen. This is the least costly process being used today, but unfortunately, it has adverse environmental effects. Water electrolysis, the most basic process of extracting hydrogen and oxygen, occurs in an electrolyzer using electrochemical water splitting. PEMFcs operated in the reverse mode with-out need for liquid electrolytes and powered by renewable power generation adequately produce green hydrogen from this new process. Research is ongoing to develop other green technologies to produce the hydrogen requirements of the future.

The Paleoproterozoic Kombolgie Subgroup (1.8 Ga), McArthur Basin, Australia: Sequence stratigraphy, basin evolution, and unconformity-related uranium deposits following the Great Oxidation Event

ABSTRACTProterozoic continental sedimentary basins contain a unique record of the evolving Earth in their sedimentology and stratigraphy and in the large-scale, redox-sensitive mineral deposits they host. The Paleoproterozoic (Stratherian) Kombolgie Basin, located on the Arnhem Land Plateau, Northern Territory, is an exceptionally well preserved, early part of the larger McArthur Basin in northern Australia. This intracratonic basin is filled with 1 to 2 km-thick, relatively undeformed, nearly flat-lying, siliciclastic rocks of the Kombolgie Subgroup. Numerous drill cores and outcrop exposures from across the basin allow sedimentary fabrics, structures, and stratigraphic relationships to be studied in great detail, providing an extensive stratigraphic framework and record of basin development and evolution.Tectonic events controlled the internal stratigraphic architecture of the basin and led to the formation of three unconformity-bounded sequences that are punctuated by volcanic events. The first sequence records the onset of basin formation and is comprised of coarse-grained sandstone and polymict lithic conglomerate deposited in proximal braided rivers that transported sediment away from basin margins and intra-basin paleohighs associated with major uranium mineralization. Paleo-currents in the upper half of this lower sequence, as well as those of overlying sequences, are directed southward and indicate that the major intra-basin topographic highs no longer existed. The middle sequence has a similar pattern of coarse-grained fluvial facies, followed by distal fluvial facies, and finally interbedded marine and eolian facies. An interval marked by mud-rich, fine-grained sandstones and mud-cracked siltstones representing tidal deposition tops this sequence. The uppermost sequence is dominated by distal fluvial and marine facies that contain halite casts, gypsum nodules, stromatolites, phosphate, and “glauconite” (a blue-green mica group mineral), indicating a marine transgression. The repeating pattern of stratigraphic sequences initiated by regional tectonic events produced well-defined coarse-grained diagenetic aquifers capped by intensely cemented distal fluvial, shoreface, eolian, and even volcanic units, and led to a well-defined heterogenous hydrostratigraphy. Basinal brines migrated within this hydrostratigraphy and, combined with paleotopography, dolerite intrusion, faulting, and intense burial diagenesis, led to the economically important uranium deposits the Kombolgie Basin hosts.Proterozoic sedimentary basins host many of Earth's largest high-grade iron and uranium deposits that formed in response to the initial oxygenation of the hydrosphere and atmosphere following the Great Oxygenation Event. Unconformity-related uranium mineralization like that found in the Kombolgie Basin highlights the interconnected role that oxygenation of the Earth, sedimentology, stratigraphy, and diagenesis played in creating these deposits.

Early Cambrian oceanic oxygenation and evolution of early animals: A critical review from the South China Craton

Co-evolution of marine redox conditions and early animals during the early Cambrian was fundamental to the development of modern Earth ecosystem. Numerous Burgess Shale-type fossil Lagerstätten (i.e., the Chengjiang and Qingjiang biotas) in South China offer taphonomic windows to probe the evolutionary traits of early animals and marine redox variations, and to evaluate the relationship between the two during the Cambrian Ages 2 and 3 (~529 to 514 Ma). Here, we critically review records of various geochemical proxies and fossil assemblages from 24 Lagerstätten-bearing lower Cambrian sections representing a wide variety of depositional settings from the deep basin to inner shelf across the Nanhua Basin, South China. Geochemical redox proxies: Fe speciation, and Mo and U enrichment factors were utilized to reconstruct water depth-related redox gradients within the early Cambrian Nanhua Basin. The results show that a dynamic ‘euxinic wedge’ may have existed at the mid-depth, and its expansion/contraction may have controlled redox variations in the Nanhua Basin during the early Cambrian. The dramatic contraction of the euxinic wedge in the Cambrian Age 3 suggests that local oceanic oxygenated states coincided with the emergence of the Chengjiang and Qingjiang biotas. Meanwhile, a ~ 25‰ negative shift in pyrite sulfur isotopes deciphers a major increase in seawater sulfate availability, reflecting strongly enhanced subaerial oxidative weathering and/or a lower burial flux of pyrite. Concurrent variations in U and Mo isotopes support the global extent of this ocean oxygenation event. Accordingly, the global marine oxygenation may have facilitated the emergence of both ecologic complexity and biodiversification of early animals indicated by the Chengjiang and Qingjiang Lagerstätten in the early Cambrian (mainly Cambrian Age 3).