Investigation of Isotopic and Geochemical Evidence for an Active Planktonic Biota in the Precambrian

The funded research was motivated by the earlier study of Burdett et al. (1990), who collected carbon and oxygen isotopic data from Paleoproterozoic rocks of the Northwest Territories from deep-and shallow-water facies of the Rocknest Platform. Their results displayed a possible decrease in (delta)C-13 with depth when arranged by increasing distance from the paleoshore. The most C-13-depleted samples were seafloor cements and fans from the underlying siliciclastic Odjick Formation, and slope carbonates of the Rocknest platform

An 80-million-year sulphur isotope record of pyrite burial over the Permian–Triassic

Despite the extensive use of sulphur isotope ratios (δ34S) for understanding ancient biogeochemical cycles, many studies focus on specific time-points of interest, such as the end-Permian mass extinction (EPME). We have generated an 80 million-year Permian–Triassic δ34Sevap curve from the Staithes S-20 borehole, Yorkshire, England. The Staithes δ34Sevap record replicates the major features of the global curve, while confirming a new excursion at the Olenekian/Anisian boundary at ~ 247 million years ago. We incorporate the resultant δ34Sevap curve into a sulphur isotope box model. Our modelling approach reveals three significant pyrite burial events (i.e. PBEs) in the Triassic. In particular, it predicts a significant biogeochemical response across the EPME, resulting in a substantial increase in pyrite burial, possibly driven by Siberian Traps volcanism. Our model suggests that after ~ 10 million years pyrite burial achieves relative long-term stability until the latest Triassic

Ocean Acidification in Deep Time

Is there precedence in Earth history for the rapid release of carbon dioxide (CO2) by fossil-fuel burning and its environmental consequences? Proxy evidence indicates that atmospheric CO2 concentrations were higher during long warm intervals in the geologic past, and that these conditions did not prevent the precipitation and accumulation of calcium carbonate (CaCO3) as limestone; accumulation of alkalinity brought to the ocean by rivers kept surface waters supersaturated. But these were steady states, not perturbations. More rapid additions of carbon dioxide during extreme events in Earth history, including the end-Permian mass extinction (251 million years ago) and the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) may have driven surface waters to undersaturation, although the evidence supporting this assertion is weak. Nevertheless, observations and modeling clearly show that during the PETM the deep ocean, at least, became highly corrosive to CaCO3. These same models applied to modern fossil fuel release project a substantial decline in surface water saturation state in the next century. So, the answer to the original question may be no, there may be no precedent in Earth history for the type of disruption we might expect from the phenomenally rapid rate of carbon addition associated with fossil fuel burning

Geochemical evidence for widespread euxinia in the Later Cambrian ocean

Widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long-term inhibitor of evolutionary radiation on early Earth. In recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later Cambrian oceans1, 2, possibly influencing evolutionary events during this time1, 2, 3. Physical evidence of widespread anoxia in Cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored. Here we present sulphur isotope records from six globally distributed stratigraphic sections of later Cambrian marine rocks (about 499 million years old). We find a positive sulphur isotope excursion in phase with the Steptoean Positive Carbon Isotope Excursion (SPICE), a large and rapid excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation4, 5. Numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large-scale anoxic and sulphidic (euxinic) conditions. Independently, molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia. These results identify the SPICE interval as the best characterized ocean anoxic event in the pre-Mesozoic ocean and an extreme example of oxygen deficiency in the later Cambrian ocean. Thus, a redox structure similar to those in Proterozoic oceans6, 7, 8 may have persisted or returned in the oceans of the early Phanerozoic eon. Indeed, the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in Cambrian oceans.Organismic and Evolutionary Biolog

Spatial patterns of climate change across the Paleocene–Eocene Thermal Maximum

This study was supported by Heising–Simons Founda-tion Grants 2016-015 (to J.E.T.), 2016-011 (to M.L. and L.R.K.), 2016-013 (toA.R.), 2016-014 (to G.J.H.), and 2016-012 (to C.J.P.). R.D.M.W. and J.W.B.R. acknowledge funding from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Program Grant 805246. This material is based on work supported by the National Center for Atmospheric Research (NCAR), which is a major facility sponsored by NSF Cooperative Agreement 1852977. Computing and data storage resources, including the Cheyenne supercomputer (https://arc.ucar.edu/knowledgebase/70549542), were provided by the Computational and Information Systems Laboratory at NCAR.The Paleocene–Eocene Thermal Maximum (PETM; 56 Ma) is one of our best geological analogs for understanding climate dynamics in a “greenhouse” world. However, proxy data representing the event are only available from select marine and terrestrial sedimentary sequences that are unevenly distributed across Earth’s surface, limiting our view of the spatial patterns of climate change. Here, we use paleoclimate data assimilation (DA) to combine climate model and proxy information and create a spatially complete reconstruction of the PETM and the climate state that precedes it (“PETM-DA”). Our data-constrained results support strong polar amplification, which in the absence of an extensive cryosphere, is related to temperature feedbacks and loss of seasonal snow on land. The response of the hydrological cycle to PETM warming consists of a narrowing of the Intertropical Convergence Zone, off-equatorial drying, and an intensification of seasonal monsoons and winter storm tracks. Many of these features are also seen in simulations of future climate change under increasing anthropogenic emissions. Since the PETM-DA yields a spatially complete estimate of surface air temperature, it yields a rigorous estimate of global mean temperature change (5.6 ∘C; 5.4 ∘C to 5.9 ∘C, 95% CI) that can be used to calculate equilibrium climate sensitivity (ECS). We find that PETM ECS was 6.5 ∘C (5.7 ∘C to 7.4 ∘C, 95% CI), which is much higher than the present-day range. This supports the view that climate sensitivity increases substantially when greenhouse gas concentrations are high.Publisher PDFPeer reviewe

Proposed initiative would study Earth's weathering engine

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94818/1/eost14765.pd

Earth: Atmospheric Evolution of a Habitable Planet

Our present-day atmosphere is often used as an analog for potentially habitable exoplanets, but Earth's atmosphere has changed dramatically throughout its 4.5 billion year history. For example, molecular oxygen is abundant in the atmosphere today but was absent on the early Earth. Meanwhile, the physical and chemical evolution of Earth's atmosphere has also resulted in major swings in surface temperature, at times resulting in extreme glaciation or warm greenhouse climates. Despite this dynamic and occasionally dramatic history, the Earth has been persistently habitable--and, in fact, inhabited--for roughly 4 billion years. Understanding Earth's momentous changes and its enduring habitability is essential as a guide to the diversity of habitable planetary environments that may exist beyond our solar system and for ultimately recognizing spectroscopic fingerprints of life elsewhere in the Universe. Here, we review long-term trends in the composition of Earth's atmosphere as it relates to both planetary habitability and inhabitation. We focus on gases that may serve as habitability markers (CO2, N2) or biosignatures (CH4, O2), especially as related to the redox evolution of the atmosphere and the coupled evolution of Earth's climate system. We emphasize that in the search for Earth-like planets we must be mindful that the example provided by the modern atmosphere merely represents a single snapshot of Earth's long-term evolution. In exploring the many former states of our own planet, we emphasize Earth's atmospheric evolution during the Archean, Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of potential atmospheric trajectories into the distant future, many millions to billions of years from now. All of these 'Alternative Earth' scenarios provide insight to the potential diversity of Earth-like, habitable, and inhabited worlds.Comment: 34 pages, 4 figures, 4 tables. Review chapter to appear in Handbook of Exoplanet