Microbialites provide a unique insight into ancient microbial processes and environments, but trends in the diversity of unlaminated microbialites remain poorly understood. The ca. 745 Ma Callison Lake Formation in the Yukon (northwest Canada) features a range of microbialites which are diverse at both the mesoscale and microscale. Four microbialite facies are recognised from the Ramp member of the Callison Lake Formation, all of which include framework structures with syn-depositional cavities. The thrombolite facies of the Callison Lake Formation is typified by exceptional preservation, with isopachous primary marine cements and distinct microclots that we suggest formed through early, mimetic carbonate precipitation. However, based on fine-scale textural relationships within the rock, we infer that the other microbialite textures were affected by diagenetic crystal growth, which reaffirms the importance of considering paragenetic history when describing and comparing ancient microbialites. The trace and rare earth element geochemistry of primary marine cements in the Callison Lake Formation microbialites suggests that the unit was deposited in a stratified, dominantly anoxic basin, with oxygenation above a very shallow chemocline. The relative depletion of chalcophile elements implies a euxinic depositional setting. This case study highlights the complexity of unlaminated microbialites and emphasises the need for detailed documentation of microbialites at multiple scales.

Geochemical data from sedimentary rocks are the primary source of information regarding Earth's surface evolution through time, including its air and water envelopes and interactions with life and deep Earth processes. The Sedimentary Geochemistry and Paleoenvironments Project (SGP) is a scientific consortium centered around open data and community-driven development of cyberinfrastructure tools and resources for sedimentary geochemistry and Earth history. Here we describe the SGP Phase 2 data release, which focused on incorporating Paleoproterozoic and Mesoproterozoic (2500–1000 million years ago) data and better accommodating carbonate data. This data release was built through the involvement of >200 researchers worldwide in academia, government, and industry, and provides the largest available public data resource for our user community in the academic fields of geochemistry, sedimentology, tectonics, paleontology, Earth history, and paleoclimate, as well as the petroleum and minerals industries. The dataset now encompasses 126,006 samples and 4,132,371 geochemical analyses. In addition to direct entry by SGP Team Members, we have ingested and incorporated datasets from the Geoscience Australia OZCHEM database, the Alberta Geological Survey, and the Deep-Time Marine Sedimentary Element Database (DM-SED) compilation. This paper details sampling in the Phase 2 dataset with respect to age, geography, lithology, and other geological characteristics, documents access via our search website and API, discusses possible issues and/or biases in the dataset that could impact analyses, describes plans for governance and stewardship of data from Indigenous lands, and serves as the citable reference paper for the data release.

The late Neoproterozoic Ediacaran Period is marked by one or more pulses of biotic turnover thought to represent intervals of global extinction, and which removed several enigmatic groups of Precambrian metazoans over a similar to 10-million-year interval in the lead-up to the Cambrian. Here, we report the discovery of putative dickinsoniomorph 'survivors' from the Nama Group of southern Namibia, including specimens preserved in place directly above an ash bed dated in this study at 538.97 +/- 0.21 Ma, and thus within error of the currently defined Ediacaran-Cambrian boundary. Some key features are poorly preserved and thus identification at this point is not definitive; however, following comparisons with a wide variety of other Ediacaran taxa and abiotic structures, we argue that interpretation as dickinsonimorph body fossils is most parsimonious. More material is undoubtedly required; however, if supported these fossils would represent the youngest dickinsoniomorph fossils found anywhere in the world, showing that this group survived the first pulse of Ediacaran extinction at similar to 550 Ma, and necessitating a re-evaluation of hypothesized drivers of late Ediacaran biotic turnover events. We suggest that these new fossil discoveries are consistent with recent models of selective extinction driven by pulses of ecological stress, reinforcing the inference that environmental perturbations were likely a crucial influence on patterns of early animal evolution prior to the main phase of the Cambrian explosion.

Resolving the biological and geological events that led to the origin of eukaryotes is an ongoing challenge in biology. A major step in the evolution of complex cellular life was the merger between an ancestral host cell and a bacterium (that became the mitochondrion) some two billion years ago. Recently, metagenomics has enabled the reconstruction of a broad diversity of genomes, referred to as the Asgard Archaea. The Asgards are monophyletic with eukaryotes on the tree of life. Asgards have an array of genes, previously thought exclusive to eukaryotes, involved in cellular trafficking, the ubiquitin system, endosomal sorting, and cytoskeleton formation, with growing evidence demonstrating the functions of these proteins mirror those in eukaryotes. This gene repertoire suggests that these Archaea are descendants of the archaeal host from which eukaryotes evolved. Increased sampling has revealed that Asgard lineages are metabolically versatile and play key roles in various ecosystems and uncovered evolutionary transitions between Archaea and eukaryotes, such as innovations in eukaryotic defense systems. The positioning of eukaryotes in the Asgards is debated, but eukaryotes appear to branch within the Heimdallarchaeia. Lineages within this group, particularly Hodarchaeales and Kariarchaeaceae, contain a broad repertoire of eukaryote-like traits, including high-energy yielding metabolisms. Observing and studying Asgard interactions with bacterial descendants of mitochondria in a modern setting will transform our understanding of the origin of complex cellular life.

Estimating dissolved oxygen (O2) concentrations in seawater during the Neoproterozoic is central to testing hypotheses about the role of O2 in animal evolution. Here we apply the thallium (Tl) isotope redox proxy to samples stratigraphically below the ca. 810-million-year-old (Ma) Bitter Springs Carbon Isotope Excursion and spanning the interval between the two Snowball Earth glaciations (ca. 662-650 Ma) to constrain the evolution of Neoproterozoic bottom water redox conditions. Thallium isotopes can be used to reconstruct the global extent of oxygenated oceanic bottom waters because the primary control on seawater Tl isotope compositions (epsilon 205Tl) over million-year time scales is changes in the amount of 205Tl removal by Mn oxides on the seafloor. Samples spanning an-20-m.y. period preceding the Bitter Springs excursion from the Tonian Reefal Assemblage (n = 18/30) yield epsilon 205Tlauth values lower than global oceanic inputs (epsilon 205Tl--2%00), with some samples approaching the modern seawater epsilon 205Tl value of-6%00. These sustained low epsilon 205Tlauth values require enhanced burial of Mn oxides elsewhere on the seafloor, which we interpret as evidence for the oxygenation of the deep ocean in the Tonian. In contrast, the majority of samples from the Cryogenian Hay Creek Group (n = 13/16) yield epsilon 205Tlauth values similar to global oceanic inputs, suggesting that the deep ocean was not ventilated at this time. This indicates that Earth's deep ocean was not gradually oxygenated throughout the Neoproterozoic, but rather experienced intervals of increased and decreased O2 concentrations.

The evolution of the eukaryotic cell paved the way for the emergence of all complex life on Earth. Despite its significance, the environmental context of early eukaryote evolution is largely unknown1,2. Here we use the geological record to reconstruct the habitats of the oldest known fossil eukaryotes, approximately 1.75-1.4 billion years old. Our integrated palaeontological, sedimentological and geochemical analyses show that although fossil eukaryotes are found in samples deposited in a range of environments from coastal to offshore, they are almost entirely restricted to those from settings with oxygenated bottom waters. This distribution suggests these organisms were aerobes (obligate, facultative and/or microaerophilic) and, given their size and morphological complexity, probably possessed mitochondria. Furthermore, their near absence from otherwise fossiliferous anoxic samples suggests a benthic habit, as planktonic eukaryotes would be expected to be present in both oxic and anoxic samples. We propose that eukaryotes were largely restricted to oxic benthic habitats for much of the Proterozoic eon, only expanding into planktonic habitats during the Neoproterozoic era (1-0.54 billion years ago). This late ecological expansion could account for the mismatch between the appearance of eukaryotic body fossils and molecular biomarkers3 and explain the stepwise increase in eukaryote diversity during the Neoproterozoic era4.

A new occurrence of Swartpuntia germsi is reported from Farm Aar near Aus in southern Namibia. It is preserved as incomplete part/counterpart in two dimensions, with a folded petaloid. Stratigraphically correlated to a minimum depositional age of 547.32 +/- 0.31 Ma, this represents the oldest global occurrence of Swartpuntia and documents a unique style of preservation within the Nama Group. Lastly, the occurrence increases the taxonomic and ecological diversity preserved at Farm Aar, making Farm Aar one of the only locations to preserve all common forms of Erniettomorph taxa.

Neoproterozoic strata of the Lomfjorden and lower Hinlopenstretet Supergroups (early-middle Tonian Veteranen Group, middle-late Tonian Akademikerbreen Group, and Cryogenian-Ediacaran Polarisbreen Group) in northeastern Svalbard, Norway, represent one of the most complete and wellpreserved terminal Proterozoic sedimentary successions worldwide. These strata have been used in numerous geochemical compilations to probe Neoproterozoic paleoenvironments, including patterns of global chemical weathering prior to the snowball Earth events. Here, we present a new high-resolution geochemical data set incorporating delta 13C, delta 18O, and 87Sr/86Sr data from carbonates with mineralogy, major-and trace-element data, and epsilon Nd data from mudrocks to critically examine previously published data sets and better ally the succession with global Neoproterozoic records through a refined age model. We found that the geochemistry of Lomfjorden and lower Hinlopenstretet Supergroup mudrocks is greatly affected by carbonate contamination and that rigorous filtering is imperative for extracting reliable provenance and weathering information. Previous studies ascribed relatively juvenile detrital Nd isotope signatures in these units to a mafic detrital source region in support of the hypothesis that basalt weathering contributed to global cooling during the Tonian prior to the Sturtian snowball Earth event. In contrast, we present a new temporally extensive epsilon Nd record that, when combined with elemental geochemical data, is best explained by the weathering of a combination of young and old granitic to granodioritic crustal sources, most likely sourced from the Grenville Province of Laurentia or Sveconorwegian Province of Scandinavia. Additionally, this new high-resolution mudrock data set allows us to assess paleoenvironmental and weathering trends within the Lomfjorden and lower Hinlopenstretet Supergroups, including the factors leading to exceptional fossil preservation in the ca. 790 Ma Algal Dolomite member of the Svanbergfjellet Formation, and post-snowball Earth weathering dynamics.

Microbial exoenzymes—extracellular enzymes secreted to degrade complex organic polymers— are essential for recycling carbon and nutrients, thus sustaining primary productivity in today’s oceans[1][1]. Yet, their evolutionary history and role in shaping Earth’s early biosphere remain entirely unexplored. Here, we trace the origins of microbial exoenzymes and reveal their previously unrecognized role in driving planetary oxygenation. Our results show that exoenzymes are more common in microorganisms utilizing high-energy metabolisms, likely reflecting the energetic costs of enzyme biosynthesis and secretion. They are especially advantageous in environments rich in particulate organic matter (POM). A refined carbon cycle model indicates that early Archean oceans offered few such habitats, as low productivity and intense UV radiation rapidly photodegraded POM. However, with a Paleoproterozoic rise of atmospheric oxygen[2][2], increased oxidative weathering boosted marine primary productivity and POM accumulation[3][3], creating conditions favoring exoenzyme evolution. Molecular clock analyses further indicate that alkaline phosphatase, a key phosphorus-releasing exoenzyme, had likely emerged with the permanent rise of oxygen, enabling more efficient phosphorus recycling. We propose that exoenzymes initiated a positive feedback loop: by accelerating nutrient regeneration, they fueled cyanobacterial productivity and oxygen release, which in turn favored greater exoenzyme capacity, reinforcing long-term oxygenation of the planet. ### Competing Interest Statement The authors have declared no competing interest. Heising-Simons Foundation, 2023-4653 New Frontiers in Research Fund Exploration grant, NFRFE-2019-00794 U.S. National Science Foundation, https://ror.org/021nxhr62, OCE-2145434 [1]: #ref-1 [2]: #ref-2 [3]: #ref-3

The middle Nama Group, deposited during the late Ediacaran in southern Namibia, is a 1 km-thick mixed carbonate-siliciclastic shallow-marine succession that displays observable regularity in its weathering profile. However, the possible role of astronomical climate forcing in this succession remains poorly understood. As a first step to understand the origin of the regularity, an initial cyclostratigraphic framework was developed using Google Earth satellite images and published U-Pb zircon ages of volcanic ash beds. Although the estimated average periodicity of 120-180 k.y. for the dominant scale of variation falls within the frequency band of astronomical forcing, it is not yet possible to discriminate between an origin related to short (~100 k.y.) eccentricity or 173 k.y. obliquity amplitude modulation. In order to refine the framework, we generated high-resolution quantitative records of the weathering profile based on drone photogrammetry. Spectral analysis on the depth series of slope steepness reveals significant spectral power related to the dominant variation at a scale of tens of meters. Additionally, it captures spectral power related to smaller-scale variations at less than 10 m. For age control, the depth series are linked to published U-Pb ages as well as to newly collected volcanic ash samples more closely tied to the analyzed sections. New high-precision dates will be crucial to determine the astronomical origin of these cycles.

Oolitic ironstones are iron-rich and chert-poor sedimentary rocks containing concentrically coated grains composed of iron (oxyhydr)oxides and iron phyllosilicates that offer a unique window into iron cycling in ancient coastal environments. These enigmatic deposits are common in the Phanerozoic stratigraphic record yet lack clear modern analogues, and curiously are thought to be absent from Precambrian strata, suggesting a secular control on their deposition. Here we describe a previously unreported ironstone from the middle Tonian (ca. 850 Ma) Katherine Group in the Wernecke Inlier (Yukon, Canada), and show that similar deposits can be found-albeit rarely-throughout the Proterozoic. We investigate the origin of this unit and evaluate its palaeoenvironmental significance, and in light of an extensive literature review, present a holistic model for Precambrian ironstone deposition. The Katherine ironstone occurs in multiple horizons in the McClure and Abraham Plains formations and contains iron ooids and oncoids composed dominantly of authigenic hematite and berthierine, with detrital quartz grains. Textural relationships demonstrate that these coated grains formed on the seafloor with synsedimentary reworking, and the fine interlamination of these phases in grain coatings suggests redox and pH fluctuation during ironstone genesis. Facies associations indicate that the ironstones accumulated in a range of low-energy, shallow marine environments (tidal mudflats and coastal embayments). Geochemical analyses offer insights into genetic processes, and the radiogenic Nd isotope composition and negative Eu anomalies of the Katherine ironstone suggest a continental iron source. We present a model whereby abundant iron, cations, and silica-requisite for the authigenesis of iron phyllosilicates-were supplied from chemical weathering and preferentially enriched in coastal environments due to gradients in pH, Eh and salinity. This continental input would have led to intense iron cycling coupled to organic matter respiration, iron phyllosilicate authigenesis (i.e., reverse weathering). The enrichment of authigenic Fe(III) (oxyhydr)oxides and Fe(II) phyllosilicates took place on a broad coastal plain influenced by both autogenic and allogenic fluctuations in relative sea level, likely in a humid, tropical climate. The lenticular and episodic nature of ironstones in the Proterozoic stratigraphic record suggests that a unique combination of environmental conditions fostered ironstone accumulation. By reviewing the literature on oolitic ironstones, we re-evaluate the temporal distribution of these deposits compared to Archaean-Palaeoproterozoic iron formations, and show that the Great Oxidation Event may have been a prerequisite for ironstone deposition, which may implicate oxidative chemical weathering or suboxic, marine iron cycling. In general, we suggest that the Precambrian record of oolitic ironstones represents an important deep-time archive of iron and nutrient cycling in coastal settings.

Tonian (ca. 1000-720 Ma) marine environments are hypothesised to have experienced major redox changes coinciding with the evolution and diversification of multicellular eukaryotes. In particular, the earliest Tonian stratigraphic record features the colonisation of benthic habitats by multicellular macroscopic algae, which would have been powerful ecosystem engineers that contributed to the oxygenation of the oceans and the reorganisation of biogeochemical cycles. However, the paleoredox context of this expansion of macroalgal habitats in Tonian nearshore marine environments remains uncertain due to limited well-preserved fossils and stratigraphy. As such, the interdependent relationship between early complex life and ocean redox state is unclear. An assemblage of macrofossils including the chlorophyte macroalga Archaeochaeta guncho was recently discovered in the lower Mackenzie Mountains Supergroup in Yukon (Canada), which archives marine sedimentation from ca. 950-775 Ma, permitting investigation into environmental evolution coincident with eukaryotic ecosystem evolution and expansion. Here we present multi-proxy geochemical data from the lower Mackenzie Mountains Supergroup to constrain the paleoredox environment within which these large benthic macroalgae thrived. Two transects show evidence for basin-wide anoxic (ferruginous) oceanic conditions (i.e., high FeHR/FeT, low Fepy/FeHR), with muted redox-sensitive trace metal enrichments and possible seasonal variability. However, the weathering of sulfide minerals in the studied samples may obscure geochemical signatures of euxinic conditions. These results suggest that macroalgae colonized shallow environments in an ocean that remained dominantly anoxic with limited evidence for oxygenation until ca. 850 Ma. Collectively, these geochemical results provide novel insights into the environmental conditions surrounding the evolution and expansion of benthic macroalgae and the eventual dominance of oxygenated oceanic conditions required for the later emergence of animals.

A geologically rapid Neoproterozoic oxygenation event is commonly linked to the appearance of marine animal groups in the fossil record. However, there is still debate about what evidence from the sedimentary geochemical record—if any—provides strong support for a persistent shift in surface oxygen immediately preceding the rise of animals. We present statistical learning analyses of a large dataset of geochemical data and associated geological context from the Neoproterozoic and Palaeozoic sedimentary record and then use Earth system modelling to link trends in redox-sensitive trace metal and organic carbon concentrations to the oxygenation of Earth’s oceans and atmosphere. We do not find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era. We do, however, reconstruct a moderate long-term increase in atmospheric oxygen and marine productivity. These changes to the Earth system would have increased dissolved oxygen and food supply in shallow-water habitats during the broad interval of geologic time in which the major animal groups first radiated. This approach provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation, while highlighting the importance of later Palaeozoic oxygenation in the evolution of the modern Earth system. Oxygen in shallow shelf waters rose linearly with atmospheric oxygen in the Neoproterozoic era, potentially driving the first radiation of marine animals, but widespread ocean oxygenation came later, according to reconstructions of oxygen levels and marine productivity.

The Paleozoic era begins with the final assembly of Gondwana and ends with the amalgamation of the supercontinent Pangea. Although this tectonic progression is generally well documented, one fundamental but understudied phenomenon during this era is the transition from two-way to one-way (northward) migration of peripheral terranes between Gondwana and Laurentia-Baltica from Cambrian to Ordovician time. The two-way terrane accretion was likely initiated during the opening of the Rheic Ocean at ca. 510 Ma when several Gondwana-derived terranes comprising Carolinia, Ganderia,Avalonia, and Meguma sequentially drifted from the northern margin of Gondwana and eventually collided with Laurentia or Baltica. Over the same time interval, the Laurentia-derived Cuyania terrane (a.k.a., the "Precordillera terrane" is commonly believed to have accreted to the proto-Andean margin of Gondwana, whereas the peri-Laurentian/Dashwoods ribbon continent separated from, then re-accreted to, the Laurentian margin after being trapped during the collision of the Taconic arc. Alternatively, the Cuyania terrane is suggested to have remained attached to the Ouachita Embayment throughout the Cambrian-Ordovician, and then passed onto Gondwana during the collision between the proto-Andean margin and the hypothesized Texas Plateau at the leading edge of Cuyania. Here we explain the enigmatic, pene-contemporaneous-migration of these peripheral terranes by a trans--Iapetus transform fault that was likely active between 510 and 450 Ma and extended from the proto-Appalachian margin of Laurentia to the proto-Andean margin of Gondwana. The trans-Iapetus transform fault terminated after the respective accretion of Carolinia and Ganderia to the proto-Appalachian margin and of Cuyania to the proto-Andean margin. We interpret the development of the transIapetus transform during the Cambrian-Ordovician to be a consequence of the global geodynamic transition from the break-up of Rodinia (-continents/terranes drifting away from Laurentia) to Pangea amalgamation (continents/terranes drifting toward assembling Laurussia).

An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.