Publications by authors named "Noah J Planavsky"

39 Publications

Global aerobics before Earth's oxygenation.

Nat Ecol Evol 2021 04;5(4):407-408

Department of Geological Sciences, Stanford University, Stanford, CA, USA.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41559-021-01404-4DOI Listing
April 2021

Weathering, alteration and reconstructing Earth's oxygenation.

Interface Focus 2020 Aug 12;10(4):20190140. Epub 2020 Jun 12.

Department of Geosciences, Eberhard-Karls University of Tuebingen, Tuebingen, Germany.

Deciphering the role-if any-that free oxygen levels played in controlling the timing and tempo of the radiation of complex life is one of the most fundamental questions in Earth and life sciences. Accurately reconstructing Earth's redox history is an essential part of tackling this question. Over the past few decades, there has been a proliferation of research employing geochemical redox proxies in an effort to tell the story of Earth's oxygenation. However, many of these studies, even those considering the same geochemical proxy systems, have led to conflicting interpretations of the timing and intensity of oxygenation events. There are two potential explanations for conflicting redox reconstructions: (i) that free oxygen levels were incredibly dynamic in both time and space or (ii) that collectively, as a community-including the authors of this article-we have frequently studied rocks affected by secondary weathering and alteration (particularly secondary oxidation) while neglecting to address the impact of this alteration on the generated data. There are now multiple case studies that have documented previously overlooked secondary alteration, resolving some of the conflicting constrains regarding redox evolution. Here, an analysis of a large shale geochemistry database reveals significant differences in cerium (Ce) anomalies, a common palaeoredox proxy, between outcrop and drill core samples. This inconsistency provides support for the idea that geochemical data from altered samples are frequently published in the peer-reviewed literature. As individuals and a geochemical community, most of us have been slow to appreciate how pervasive the problem is but there are examples of other communities that have faced and met the challenges raised by such quality control crises. Further evidence of the high potential for alteration of deep-time geochemical samples, and recognition of the manner in which this may lead to spurious results and palaeoenvironmental interpretations, indicate that sample archiving, in publicly accessible collections needs to become a prerequisite for publication of new palaeoredox data. Finally, the geochemical community need to think about ways to implement additional quality control measures to increase the fidelity of palaeoredox proxy work.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rsfs.2019.0140DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7333904PMC
August 2020

Persistent global marine euxinia in the early Silurian.

Nat Commun 2020 04 14;11(1):1804. Epub 2020 Apr 14.

Stanford University, Department of Geological Sciences, Stanford, CA, 94305, USA.

The second pulse of the Late Ordovician mass extinction occurred around the Hirnantian-Rhuddanian boundary (~444 Ma) and has been correlated with expanded marine anoxia lasting into the earliest Silurian. Characterization of the Hirnantian ocean anoxic event has focused on the onset of anoxia, with global reconstructions based on carbonate δU modeling. However, there have been limited attempts to quantify uncertainty in metal isotope mass balance approaches. Here, we probabilistically evaluate coupled metal isotopes and sedimentary archives to increase constraint. We present iron speciation, metal concentration, δMo and δU measurements of Rhuddanian black shales from the Murzuq Basin, Libya. We evaluate these data (and published carbonate δU data) with a coupled stochastic mass balance model. Combined statistical analysis of metal isotopes and sedimentary sinks provides uncertainty-bounded constraints on the intensity of Hirnantian-Rhuddanian euxinia. This work extends the duration of anoxia to >3 Myrs - notably longer than well-studied Mesozoic ocean anoxic events.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-15400-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7156380PMC
April 2020

Large Mass-Independent Oxygen Isotope Fractionations in Mid-Proterozoic Sediments: Evidence for a Low-Oxygen Atmosphere?

Astrobiology 2020 05 31;20(5):628-636. Epub 2020 Mar 31.

Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel.

Earth's ocean-atmosphere system has undergone a dramatic but protracted increase in oxygen (O) abundance. This environmental transition ultimately paved the way for the rise of multicellular life and provides a blueprint for how a biosphere can transform a planetary surface. However, estimates of atmospheric oxygen levels for large intervals of Earth's history still vary by orders of magnitude-foremost for Earth's middle history. Historically, estimates of mid-Proterozoic (1.9-0.8 Ga) atmospheric oxygen levels are inferred based on the kinetics of reactions occurring in soils or in the oceans, rather than being directly tracked by atmospheric signatures. Rare oxygen isotope systematics-based on quantifying the rare oxygen isotope O in addition to the conventionally determined O and O-provide a means to track atmospheric isotopic signatures and thus potentially provide more direct estimates of atmospheric oxygen levels through time. Oxygen isotope signatures that deviate strongly from the expected mass-dependent relationship between O, O, and O develop during ozone formation, and these "mass-independent" signals can be transferred to the rock record during oxidation reactions in surface environments that involve atmospheric O. The magnitude of these signals is dependent upon O, CO, and the overall extent of biospheric productivity. Here, we use a stochastic approach to invert the mid-Proterozoic ΔO record for a new estimate of atmospheric O, leveraging explicit coupling of O and biospheric productivity in a biogeochemical Earth system model to refine the range of atmospheric O values that is consistent with a given observed ΔO. Using this approach, we find new evidence that atmospheric oxygen levels were less than ∼1% of the present atmospheric level (PAL) for at least some intervals of the Proterozoic Eon.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1089/ast.2019.2060DOI Listing
May 2020

On the co-evolution of surface oxygen levels and animals.

Geobiology 2020 05 16;18(3):260-281. Epub 2020 Mar 16.

Department of Geology and Geophysics, Yale University, New Haven, Connecticut.

Few topics in geobiology have been as extensively debated as the role of Earth's oxygenation in controlling when and why animals emerged and diversified. All currently described animals require oxygen for at least a portion of their life cycle. Therefore, the transition to an oxygenated planet was a prerequisite for the emergence of animals. Yet, our understanding of Earth's oxygenation and the environmental requirements of animal habitability and ecological success is currently limited; estimates for the timing of the appearance of environments sufficiently oxygenated to support ecologically stable populations of animals span a wide range, from billions of years to only a few million years before animals appear in the fossil record. In this light, the extent to which oxygen played an important role in controlling when animals appeared remains a topic of debate. When animals originated and when they diversified are separate questions, meaning either one or both of these phenomena could have been decoupled from oxygenation. Here, we present views from across this interpretive spectrum-in a point-counterpoint format-regarding crucial aspects of the potential links between animals and surface oxygen levels. We highlight areas where the standard discourse on this topic requires a change of course and note that several traditional arguments in this "life versus environment" debate are poorly founded. We also identify a clear need for basic research across a range of fields to disentangle the relationships between oxygen availability and emergence and diversification of animal life.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gbi.12382DOI Listing
May 2020

The impact of marine nutrient abundance on early eukaryotic ecosystems.

Geobiology 2020 03 17;18(2):139-151. Epub 2020 Feb 17.

NASA Astrobiology Institute, Alternative Earths Team, Riverside, California.

The rise of eukaryotes to ecological prominence represents one of the most dramatic shifts in the history of Earth's biosphere. However, there is an enigmatic temporal lag between the emergence of eukaryotic organisms in the fossil record and their much later ecological expansion. In parallel, there is evidence for a secular increase in the availability of the key macronutrient phosphorus (P) in Earth's oceans. Here, we use an Earth system model equipped with a size-structured marine ecosystem to explore relationships between plankton size, trophic complexity, and the availability of marine nutrients. We find a strong dependence of planktonic ecosystem structure on ocean nutrient abundance, with a larger ocean nutrient inventory leading to greater overall biomass, broader size spectra, and increasing abundance of large Zooplankton. If existing estimates of Proterozoic marine nutrient levels are correct, our results suggest that increases in the ecological impact of eukaryotic algae and trophic complexity in eukaryotic ecosystems were directly linked to restructuring of the global P cycle associated with the protracted rise of surface oxygen levels. Our results thus suggest an indirect but potentially important mechanism by which ocean oxygenation may have acted to shape marine ecological function during late Proterozoic time.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gbi.12384DOI Listing
March 2020

Subglacial meltwater supported aerobic marine habitats during Snowball Earth.

Proc Natl Acad Sci U S A 2019 12 2;116(51):25478-25483. Epub 2019 Dec 2.

Department of Geology and Geophysics, Yale University, New Haven, CT 06511.

The Earth's most severe ice ages interrupted a crucial interval in eukaryotic evolution with widespread ice coverage during the Cryogenian Period (720 to 635 Ma). Aerobic eukaryotes must have survived the "Snowball Earth" glaciations, requiring the persistence of oxygenated marine habitats, yet evidence for these environments is lacking. We examine iron formations within globally distributed Cryogenian glacial successions to reconstruct the redox state of the synglacial oceans. Iron isotope ratios and cerium anomalies from a range of glaciomarine environments reveal pervasive anoxia in the ice-covered oceans but increasing oxidation with proximity to the ice shelf grounding line. We propose that the outwash of subglacial meltwater supplied oxygen to the synglacial oceans, creating glaciomarine oxygen oases. The confluence of oxygen-rich meltwater and iron-rich seawater may have provided sufficient energy to sustain chemosynthetic communities. These processes could have supplied the requisite oxygen and organic carbon source for the survival of early animals and other eukaryotic heterotrophs through these extreme glaciations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1909165116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6926012PMC
December 2019

Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact.

Proc Natl Acad Sci U S A 2019 11 21;116(45):22500-22504. Epub 2019 Oct 21.

Department of Geology & Geophysics, Yale University, New Haven, CT 06520;

Mass extinction at the Cretaceous-Paleogene (K-Pg) boundary coincides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we document a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as a mechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth system modeling, indicate that a partial ∼50% reduction in global marine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario reconciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which marine life imprints its isotopic signal onto the geological record.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1905989116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6842625PMC
November 2019

A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic.

Geobiology 2019 11 22;17(6):579-593. Epub 2019 Aug 22.

Department of Geology and Geophysics, Yale University, New Haven, CT, USA.

Atmospheric oxygen levels control the oxidative side of key biogeochemical cycles and place limits on the development of high-energy metabolisms. Understanding Earth's oxygenation is thus critical to developing a clearer picture of Earth's long-term evolution. However, there is currently vigorous debate about even basic aspects of the timing and pattern of the rise of oxygen. Chemical weathering in the terrestrial environment occurs in contact with the atmosphere, making paleosols potentially ideal archives to track the history of atmospheric O levels. Here we present stable chromium isotope data from multiple paleosols that offer snapshots of Earth surface conditions over the last three billion years. The results indicate a secular shift in the oxidative capacity of Earth's surface in the Neoproterozoic and suggest low atmospheric oxygen levels (<1% PAL pO ) through the majority of Earth's history. The paleosol record also shows that localized Cr oxidation may have begun as early as the Archean, but efficient, modern-like transport of hexavalent Cr under an O -rich atmosphere did not become common until the Neoproterozoic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gbi.12360DOI Listing
November 2019

Evidence for a prolonged Permian-Triassic extinction interval from global marine mercury records.

Nat Commun 2019 04 5;10(1):1563. Epub 2019 Apr 5.

Department of Geology and Geophysics, Yale University, New Haven, CT, 06520-8109, USA.

The latest Permian mass extinction, the most devastating biocrisis of the Phanerozoic, has been widely attributed to eruptions of the Siberian Traps Large Igneous Province, although evidence of a direct link has been scant to date. Here, we measure mercury (Hg), assumed to reflect shifts in volcanic activity, across the Permian-Triassic boundary in ten marine sections across the Northern Hemisphere. Hg concentration peaks close to the Permian-Triassic boundary suggest coupling of biotic extinction and increased volcanic activity. Additionally, Hg isotopic data for a subset of these sections provide evidence for largely atmospheric rather than terrestrial Hg sources, further linking Hg enrichment to increased volcanic activity. Hg peaks in shallow-water sections were nearly synchronous with the end-Permian extinction horizon, while those in deep-water sections occurred tens of thousands of years before the main extinction, possibly supporting a globally diachronous biotic turnover and protracted mass extinction event.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-019-09620-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6450928PMC
April 2019

Stepwise oxygenation of the Paleozoic atmosphere.

Nat Commun 2018 10 4;9(1):4081. Epub 2018 Oct 4.

School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

Oxygen is essential for animal life, and while geochemical proxies have been instrumental in determining the broad evolutionary history of oxygen on Earth, much of our insight into Phanerozoic oxygen comes from biogeochemical modelling. The GEOCARBSULF model utilizes carbon and sulphur isotope records to produce the most detailed history of Phanerozoic atmospheric O currently available. However, its predictions for the Paleozoic disagree with geochemical proxies, and with non-isotope modelling. Here we show that GEOCARBSULF oversimplifies the geochemistry of sulphur isotope fractionation, returning unrealistic values for the O sourced from pyrite burial when oxygen is low. We rebuild the model from first principles, utilizing an improved numerical scheme, the latest carbon isotope data, and we replace the sulphur cycle equations in line with forwards modelling approaches. Our new model, GEOCARBSULFOR, produces a revised, highly-detailed prediction for Phanerozoic O that is consistent with available proxy data, and independently supports a Paleozoic Oxygenation Event, which likely contributed to the observed radiation of complex, diverse fauna at this time.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-018-06383-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6172248PMC
October 2018

A case for low atmospheric oxygen levels during Earth's middle history.

Emerg Top Life Sci 2018 Sep;2(2):149-159

NASA Astrobiology Institute Alternative Earths Team, Riverside, CA, U.S.A.

The oxygenation of the atmosphere - one of the most fundamental transformations in Earth's history - dramatically altered the chemical composition of the oceans and provides a compelling example of how life can reshape planetary surface environments. Furthermore, it is commonly proposed that surface oxygen levels played a key role in controlling the timing and tempo of the origin and early diversification of animals. Although oxygen levels were likely more dynamic than previously imagined, we make a case here that emerging records provide evidence for low atmospheric oxygen levels for the majority of Earth's history. Specifically, we review records and present a conceptual framework that suggest that background oxygen levels were below 1% of the present atmospheric level during the billon years leading up to the diversification of early animals. Evidence for low background oxygen levels through much of the Proterozoic bolsters the case that environmental conditions were a critical factor in controlling the structure of ecosystems through Earth's history.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1042/ETLS20170161DOI Listing
September 2018

Reverse weathering as a long-term stabilizer of marine pH and planetary climate.

Nature 2018 08 8;560(7719):471-475. Epub 2018 Aug 8.

Department of Geology and Geophysics, Yale University, New Haven, CT, USA.

For the first four billion years of Earth's history, climate was marked by apparent stability and warmth despite the Sun having lower luminosity. Proposed mechanisms for maintaining an elevated partial pressure of carbon dioxide in the atmosphere ([Formula: see text]) centre on a reduction in the weatherability of Earth's crust and therefore in the efficiency of carbon dioxide removal from the atmosphere. However, the effectiveness of these mechanisms remains debated. Here we use a global carbon cycle model to explore the evolution of processes that govern marine pH, a factor that regulates the partitioning of carbon between the ocean and the atmosphere. We find that elevated rates of 'reverse weathering'-that is, the consumption of alkalinity and generation of acidity during marine authigenic clay formation-enhanced the retention of carbon within the ocean-atmosphere system, leading to an elevated [Formula: see text] baseline. Although this process is dampened by sluggish kinetics today, we propose that more prolific rates of reverse weathering would have persisted under the pervasively silica-rich conditions that dominated Earth's early oceans. This distinct ocean and coupled carbon-silicon cycle state would have successfully maintained the equable and ice-free environment that characterized most of the Precambrian period. Further, we propose that during this time, the establishment of a strong negative feedback between marine pH and authigenic clay formation would have also enhanced climate stability by mitigating large swings in [Formula: see text]-a critical component of Earth's natural thermostat that would have been dominant for most of Earth's history. We speculate that the late ecological rise of siliceous organisms and a resulting decline in silica-rich conditions dampened the reverse weathering buffer, destabilizing Earth's climate system and lowering baseline [Formula: see text].
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41586-018-0408-4DOI Listing
August 2018

UV radiation limited the expansion of cyanobacteria in early marine photic environments.

Nat Commun 2018 08 6;9(1):3088. Epub 2018 Aug 6.

Earth and Atmospheric Sciences, University of Alberta, Edmonton, T6G 2E3, AB, Canada.

Prior to atmospheric oxygenation, ecosystems were exposed to higher UV radiation fluxes relative to modern surface environments. Iron-silica mineral coatings have been evoked as effective UV radiation shields in early terrestrial settings. Here we test whether similar protection applied to planktonic cyanobacteria within the Archean water column. Based on experiments done under Archean seawater conditions, we report that Fe(III)-Si-rich precipitates absorb up to 70% of incoming UV-C radiation, with a reduction of <20% in photosynthetically active radiation flux. However, we demonstrate that even short periods of UV-C irradiation in the presence of Fe(III)-Si precipitates resulted in high mortality rates, and suggest that these effects would have persisted throughout much of the photic zone. Our findings imply that despite the shielding properties of Fe(III)-Si-rich precipitates in the early water column, UV radiation would continue to limit cyanobacterial expansion and likely had a greater effect on Archean ecosystem structure before the formation of an ozone layer.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-018-05520-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6079077PMC
August 2018

Constraints on Paleoproterozoic atmospheric oxygen levels.

Proc Natl Acad Sci U S A 2018 08 23;115(32):8104-8109. Epub 2018 Jul 23.

Department of Geology and Geophysics, Yale University, New Haven, CT 06511.

The oxygenation of Earth's surface environment dramatically altered key biological and geochemical cycles and ultimately ushered in the rise of an ecologically diverse biosphere. However, atmospheric oxygen partial pressures (O) estimates for large swaths of the Precambrian remain intensely debated. Here we evaluate and explore the use of carbonate cerium (Ce) anomalies (Ce/Ce*) as a quantitative atmospheric O proxy and provide estimates of Proterozoic O using marine carbonates from a unique Precambrian carbonate succession-the Paleoproterozoic Pethei Group. In contrast to most previous work, we measure Ce/Ce* on marine carbonate precipitates that formed in situ across a depth gradient, building on previous detailed sedimentology and stratigraphy to constrain the paleo-depth of each sample. Measuring Ce/Ce* across a full platform to basin depth gradient, we found only minor depleted Ce anomalies restricted to the platform and upper slope facies. We combine these results with a Ce oxidation model to provide a quantitative constraint on atmospheric O 1.87 billion years ago (Ga). Our results suggest Paleoproterozoic atmospheric oxygen concentrations were low, near 0.1% of the present atmospheric level. This work provides another crucial line of empirical evidence that atmospheric oxygen levels returned to low concentrations following the Lomagundi Event, and remained low enough for large portions of the Proterozoic to have impacted the ecology of the earliest complex organisms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1806216115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6094116PMC
August 2018

Triple oxygen isotope evidence for limited mid-Proterozoic primary productivity.

Nature 2018 07 18;559(7715):613-616. Epub 2018 Jul 18.

University of Colorado Boulder, Boulder, CO, USA.

The global biosphere is commonly assumed to have been less productive before the rise of complex eukaryotic ecosystems than it is today. However, direct evidence for this assertion is lacking. Here we present triple oxygen isotope measurements (∆O) from sedimentary sulfates from the Sibley basin (Ontario, Canada) dated to about 1.4 billion years ago, which provide evidence for a less productive biosphere in the middle of the Proterozoic eon. We report what are, to our knowledge, the most-negative ∆O values (down to -0.88‰) observed in sulfates, except for those from the terminal Cryogenian period. This observation demonstrates that the mid-Proterozoic atmosphere was distinct from what persisted over approximately the past 0.5 billion years, directly reflecting a unique interplay among the atmospheric partial pressures of CO and O and the photosynthetic O flux at this time. Oxygenic gross primary productivity is stoichiometrically related to the photosynthetic O flux to the atmosphere. Under current estimates of mid-Proterozoic atmospheric partial pressure of CO (2-30 times that of pre-anthropogenic levels), our modelling indicates that gross primary productivity was between about 6% and 41% of pre-anthropogenic levels if atmospheric O was between 0.1-1% or 1-10% of pre-anthropogenic levels, respectively. When compared to estimates of Archaean and Phanerozoic primary production, these model solutions show that an increasingly more productive biosphere accompanied the broad secular pattern of increasing atmospheric O over geologic time.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41586-018-0349-yDOI Listing
July 2018

Earth's youngest banded iron formation implies ferruginous conditions in the Early Cambrian ocean.

Sci Rep 2018 07 2;8(1):9970. Epub 2018 Jul 2.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada.

It has been proposed that anoxic and iron-rich (ferruginous) marine conditions were common through most of Earth history. This view represents a major shift in our understanding of the evolution of marine chemistry. However, thus far, evidence for ferruginous conditions comes predominantly from Fe-speciation data. Given debate over these records, new evidence for Fe-rich marine conditions is a requisite if we are to shift our view regarding evolution of the marine redox landscape. Here we present strong evidence for ferruginous conditions by describing a suite of Fe-rich chemical sedimentary rocks-banded iron formation (BIF)--deposited during the Early Cambrian in western China. Specifically, we provide new U-Pb geochronological data that confirm a depositional age of ca. 527 Ma for this unit, as well as rare earth element (REE) data are consistent with anoxic deposition. Similar to many Algoma-type Precambrian iron formations, these Early Cambrian sediments precipitated in a back-arc rift basin setting, where hydrothermally sourced iron drove the deposition of a BIF-like protolith, the youngest ever reported of regional extent without direct links to volcanogenic massive sulphide (VMS) deposits. Their presence indicates that marine environments were still characterized by chemical- and redox-stratification, thus supporting the view that-despite a dearth of modern marine analogues-ferruginous conditions continued to locally be a feature of early Phanerozoic seawater.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-018-28187-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6028650PMC
July 2018

Tracking the rise of eukaryotes to ecological dominance with zinc isotopes.

Geobiology 2018 07 5;16(4):341-352. Epub 2018 Jun 5.

Geology and Geophysics, Yale University, New Haven, Connecticut.

The biogeochemical cycling of zinc (Zn) is intimately coupled with organic carbon in the ocean. Based on an extensive new sedimentary Zn isotope record across Earth's history, we provide evidence for a fundamental shift in the marine Zn cycle ~800 million years ago. We discuss a wide range of potential drivers for this transition and propose that, within available constraints, a restructuring of marine ecosystems is the most parsimonious explanation for this shift. Using a global isotope mass balance approach, we show that a change in the organic Zn/C ratio is required to account for observed Zn isotope trends through time. Given the higher affinity of eukaryotes for Zn relative to prokaryotes, we suggest that a shift toward a more eukaryote-rich ecosystem could have provided a means of more efficiently sequestering organic-derived Zn. Despite the much earlier appearance of eukaryotes in the microfossil record (~1700 to 1600 million years ago), our data suggest a delayed rise to ecological prominence during the Neoproterozoic, consistent with the currently accepted organic biomarker records.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gbi.12289DOI Listing
July 2018

Redox-independent chromium isotope fractionation induced by ligand-promoted dissolution.

Nat Commun 2017 11 17;8(1):1590. Epub 2017 Nov 17.

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, 30332, USA.

The chromium (Cr) isotope system has emerged as a potential proxy for tracing the Earth's atmospheric evolution based on a redox-dependent framework for Cr mobilization and isotope fractionation. Although studies have demonstrated that redox-independent pathways can also mobilize Cr, no quantitative constraints exist on the associated isotope fractionations. Here we survey the effects of common environmental ligands on the dissolution of Cr(III)-(oxy)hydroxide solids and associated Cr isotope fractionation. For a variety of organic acids and siderophores, δCr values of dissolved Cr(III) are -0.27 to 1.23‰, within the range of previously observed Cr isotope signatures in rock records linked to Cr redox cycling. Thus, ligand-promoted dissolution of Cr-containing solids, a redox-independent process, must be taken into account when using sedimentary Cr isotope signatures to diagnose atmospheric oxygen levels. This work provides a step towards establishing a more robust framework for using Cr isotopes to track the evolution of the Earth's atmosphere.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-017-01694-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693864PMC
November 2017

A Study of the Microbial Spatial Heterogeneity of Bahamian Thrombolites Using Molecular, Biochemical, and Stable Isotope Analyses.

Astrobiology 2017 May;17(5):413-430

1 Department of Microbiology and Cell Science, University of Florida , Space Life Sciences Lab, Merritt Island, Florida.

Thrombolites are buildups of carbonate that exhibit a clotted internal structure formed through the interactions of microbial mats and their environment. Despite recent advances, we are only beginning to understand the microbial and molecular processes associated with their formation. In this study, a spatial profile of the microbial and metabolic diversity of thrombolite-forming mats of Highborne Cay, The Bahamas, was generated by using 16S rRNA gene sequencing and predictive metagenomic analyses. These molecular-based approaches were complemented with microelectrode profiling and in situ stable isotope analysis to examine the dominant taxa and metabolic activities within the thrombolite-forming communities. Analyses revealed three distinctive zones within the thrombolite-forming mats that exhibited stratified populations of bacteria and archaea. Predictive metagenomics also revealed vertical profiles of metabolic capabilities, such as photosynthesis and carboxylic and fatty acid synthesis within the mats that had not been previously observed. The carbonate precipitates within the thrombolite-forming mats exhibited isotopic geochemical signatures suggesting that the precipitation within the Bahamian thrombolites is photosynthetically induced. Together, this study provides the first look at the spatial organization of the microbial populations within Bahamian thrombolites and enables the distribution of microbes to be correlated with their activities within modern thrombolite systems. Key Words: Thrombolites-Microbial diversity-Metagenome-Stable isotopes-Microbialites. Astrobiology 17, 413-430.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1089/ast.2016.1563DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5767104PMC
May 2017

Global water cycle and the coevolution of the Earth's interior and surface environment.

Philos Trans A Math Phys Eng Sci 2017 May;375(2094)

Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA.

The bulk Earth composition contains probably less than 0.3% of water, but this trace amount of water can affect the long-term evolution of the Earth in a number of different ways. The foremost issue is the occurrence of plate tectonics, which governs almost all aspects of the Earth system, and the presence of water could either promote or hinder the operation of plate tectonics, depending on where water resides. The global water cycle, which circulates surface water into the deep mantle and back to the surface again, could thus have played a critical role in the Earth's history. In this contribution, we first review the present-day water cycle and discuss its uncertainty as well as its secular variation. If the continental freeboard has been roughly constant since the Early Proterozoic, model results suggest long-term net water influx from the surface to the mantle, which is estimated to be 3-4.5×10 g yr on the billion years time scale. We survey geological and geochemical observations relevant to the emergence of continents above the sea level as well as the nature of Precambrian plate tectonics. The global water cycle is suggested to have been dominated by regassing, and its implications for geochemical cycles and atmospheric evolution are also discussed.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rsta.2015.0393DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5394256PMC
May 2017

Evolution of the global phosphorus cycle.

Nature 2017 01 21;541(7637):386-389. Epub 2016 Dec 21.

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada.

The macronutrient phosphorus is thought to limit primary productivity in the oceans on geological timescales. Although there has been a sustained effort to reconstruct the dynamics of the phosphorus cycle over the past 3.5 billion years, it remains uncertain whether phosphorus limitation persisted throughout Earth's history and therefore whether the phosphorus cycle has consistently modulated biospheric productivity and ocean-atmosphere oxygen levels over time. Here we present a compilation of phosphorus abundances in marine sedimentary rocks spanning the past 3.5 billion years. We find evidence for relatively low authigenic phosphorus burial in shallow marine environments until about 800 to 700 million years ago. Our interpretation of the database leads us to propose that limited marginal phosphorus burial before that time was linked to phosphorus biolimitation, resulting in elemental stoichiometries in primary producers that diverged strongly from the Redfield ratio (the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton). We place our phosphorus record in a quantitative biogeochemical model framework and find that a combination of enhanced phosphorus scavenging in anoxic, iron-rich oceans and a nutrient-based bistability in atmospheric oxygen levels could have resulted in a stable low-oxygen world. The combination of these factors may explain the protracted oxygenation of Earth's surface over the last 3.5 billion years of Earth history. However, our analysis also suggests that a fundamental shift in the phosphorus cycle may have occurred during the late Proterozoic eon (between 800 and 635 million years ago), coincident with a previously inferred shift in marine redox states, severe perturbations to Earth's climate system, and the emergence of animals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature20772DOI Listing
January 2017

Hypochloremia and Diuretic Resistance in Heart Failure: Mechanistic Insights.

Circ Heart Fail 2016 08;9(8)

From the Program of Applied Translational Research (J.S.H., V.R., J.M.t.M., O.L., F.P.W., M.A., J.S.B., C.R.P., J.M.T.) and Department of Internal Medicine (F.P.W., T.A., L.B., C.R.P., J.M.T.), Yale University School of Medicine, New Haven, CT; Department of Cardiology, University Medical Center Groningen, University of Groningen, The Netherlands (J.M.t.M.); Cardiovascular Division, Department of Medicine, Medical University of South Carolina, Charleston (M.A.B.); Clinical Epidemiology Research Center, Veterans Affairs Medical Center, West Haven, CT (F.P.W.); Section of Heart Failure and Cardiac Transplantation, the Cleveland Clinic, OH (J.L.G., W.H.W.T.); and Department of Geology and Geophysics, Yale University, New Haven, CT (N.J.P.).

Background: Recent epidemiological studies have implicated chloride, rather than sodium, as the driver of poor survival previously attributed to hyponatremia in heart failure. Accumulating basic science evidence has identified chloride as a critical factor in renal salt sensing. Our goal was to probe the physiology bridging this basic and epidemiological literature.

Methods And Results: Two heart failure cohorts were included: (1) observational: patients receiving loop diuretics at the Yale Transitional Care Center (N=162) and (2) interventional pilot: stable outpatients receiving ≥80 mg furosemide equivalents were studied before and after 3 days of 115 mmol/d supplemental lysine chloride (N=10). At the Yale Transitional Care Center, 31.5% of patients had hypochloremia (chloride ≤96 mmol/L). Plasma renin concentration correlated with serum chloride (r=-0.46; P<0.001) with no incremental contribution from serum sodium (P=0.49). Hypochloremic versus nonhypochloremic patients exhibited renal wasting of chloride (P=0.04) and of chloride relative to sodium (P=0.01), despite better renal free water excretion (urine osmolality 343±101 mOsm/kg versus 475±136; P<0.001). Hypochloremia was associated with poor diuretic response (odds ratio, 7.3; 95% confidence interval, 3.3-16.1; P<0.001). In the interventional pilot, lysine chloride supplementation was associated with an increase in serum chloride levels of 2.2±2.3 mmol/L, and the majority of participants experienced findings such as hemoconcentration, weight loss, reduction in amino terminal, pro B-type natriuretic peptide, increased plasma renin activity, and increased blood urea nitrogen to creatinine ratio.

Conclusions: Hypochloremia is associated with neurohormonal activation and diuretic resistance with chloride depletion as a candidate mechanism. Sodium-free chloride supplementation was associated with increases in serum chloride and changes in several cardiorenal parameters.

Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02031354.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1161/CIRCHEARTFAILURE.116.003180DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988527PMC
August 2016

Earth's oxygen cycle and the evolution of animal life.

Proc Natl Acad Sci U S A 2016 08 25;113(32):8933-8. Epub 2016 Jul 25.

Department of Paleobiology, National Museum of Natural History, Washington, DC 20560.

The emergence and expansion of complex eukaryotic life on Earth is linked at a basic level to the secular evolution of surface oxygen levels. However, the role that planetary redox evolution has played in controlling the timing of metazoan (animal) emergence and diversification, if any, has been intensely debated. Discussion has gravitated toward threshold levels of environmental free oxygen (O2) necessary for early evolving animals to survive under controlled conditions. However, defining such thresholds in practice is not straightforward, and environmental O2 levels can potentially constrain animal life in ways distinct from threshold O2 tolerance. Herein, we quantitatively explore one aspect of the evolutionary coupling between animal life and Earth's oxygen cycle-the influence of spatial and temporal variability in surface ocean O2 levels on the ecology of early metazoan organisms. Through the application of a series of quantitative biogeochemical models, we find that large spatiotemporal variations in surface ocean O2 levels and pervasive benthic anoxia are expected in a world with much lower atmospheric pO2 than at present, resulting in severe ecological constraints and a challenging evolutionary landscape for early metazoan life. We argue that these effects, when considered in the light of synergistic interactions with other environmental parameters and variable O2 demand throughout an organism's life history, would have resulted in long-term evolutionary and ecological inhibition of animal life on Earth for much of Middle Proterozoic time (∼1.8-0.8 billion years ago).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1521544113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987840PMC
August 2016

Continental arc volcanism as the principal driver of icehouse-greenhouse variability.

Science 2016 Apr;352(6284):444-7

Department of Earth Sciences, Rice University, Houston, TX 77005, USA.

Variations in continental volcanic arc emissions have the potential to control atmospheric carbon dioxide (CO2) levels and climate change on multimillion-year time scales. Here we present a compilation of ~120,000 detrital zircon uranium-lead (U-Pb) ages from global sedimentary deposits as a proxy to track the spatial distribution of continental magmatic arc systems from the Cryogenian period to the present. These data demonstrate a direct relationship between global arc activity and major climate shifts: Widespread continental arcs correspond with prominent early Paleozoic and Mesozoic greenhouse climates, whereas reduced continental arc activity corresponds with icehouse climates of the Cryogenian, Late Ordovician, late Paleozoic, and Cenozoic. This persistent coupled behavior provides evidence that continental volcanic outgassing drove long-term shifts in atmospheric CO2 levels over the past ~720 million years.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.aad5787DOI Listing
April 2016

No evidence for high atmospheric oxygen levels 1,400 million years ago.

Proc Natl Acad Sci U S A 2016 May 20;113(19):E2550-1. Epub 2016 Apr 20.

Department of Earth Science, University of California, Riverside, CA 92521;

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1601925113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868423PMC
May 2016

Ediacaran Marine Redox Heterogeneity and Early Animal Ecosystems.

Sci Rep 2015 Nov 24;5:17097. Epub 2015 Nov 24.

State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.

Oxygenation has widely been viewed as a major factor driving the emergence and diversification of animals. However, links between early animal evolution and shifts in surface oxygen levels have largely been limited to extrapolation of paleoredox conditions reconstructed from unfossiliferous strata to settings in which contemporaneous fossils were preserved. Herein, we present a multi-proxy paleoredox study of late Ediacaran (ca. 560-551 Ma) shales hosting the Miaohe Konservat-Lagerstätte of South China and, for comparison, equivalent non-fossil-bearing shales at adjacent sections. For the fossiliferous strata at Miaohe there is geochemical evidence for anoxic conditions, but paleontological evidence for at least episodically oxic conditions. An oxygen-stressed environment is consistent with the low diversity and simple morphology of Miaohe Biota macrofossils. However, there is no evidence for euxinic (anoxic and sulphidic) conditions for the fossiliferous strata at Miaohe, in contrast to adjacent unfossiliferous sections. Our results indicate that Ediacaran marine redox chemistry was highly heterogeneous, even at the kilometre-scale. Therefore, our study provides direct-rather than inferred-evidence that anoxia played a role in shaping a landmark Ediacaran ecosystem. If the anoxic conditions characteristic of the studied sections were widespread in the late Neoproterozoic, environmental stress would have hindered the development of complex ecosystems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep17097DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4656985PMC
November 2015

Earth history. Low mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals.

Science 2014 Oct;346(6209):635-8

Department of Earth Sciences, University of California, Riverside, CA, USA.

The oxygenation of Earth's surface fundamentally altered global biogeochemical cycles and ultimately paved the way for the rise of metazoans at the end of the Proterozoic. However, current estimates for atmospheric oxygen (O2) levels during the billion years leading up to this time vary widely. On the basis of chromium (Cr) isotope data from a suite of Proterozoic sediments from China, Australia, and North America, interpreted in the context of data from similar depositional environments from Phanerozoic time, we find evidence for inhibited oxidation of Cr at Earth's surface in the mid-Proterozoic (1.8 to 0.8 billion years ago). These data suggest that atmospheric O2 levels were at most 0.1% of present atmospheric levels. Direct evidence for such low O2 concentrations in the Proterozoic helps explain the late emergence and diversification of metazoans.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1258410DOI Listing
October 2014

Evolution: a fixed-nitrogen fix in the early ocean?

Curr Biol 2014 Mar;24(7):R276-8

Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA.

A new study asserts that a late evolutionary leap in cyanobacterial nitrogen fixation terminated a long history of nitrogen-limited primary production in the ocean--and contributed to a dramatic increase in biospheric oxygen coincident with the rise of animals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cub.2014.02.034DOI Listing
March 2014