The Earth has cooled over the past 4.5 billion years (Gyr) as a result of surface heat loss and declining radiogenic heat production. Igneous geochemistry has been used to understand how changing ...heat flux influenced Archaean geodynamics, but records of systematic geochemical evolution are complicated by heterogeneity of the rock record and uncertainties regarding selection and preservation bias. Here we apply statistical sampling techniques to a geochemical database of about 70,000 samples from the continental igneous rock record to produce a comprehensive record of secular geochemical evolution throughout Earth history. Consistent with secular mantle cooling, compatible and incompatible elements in basalts record gradually decreasing mantle melt fraction through time. Superimposed on this gradual evolution is a pervasive geochemical discontinuity occurring about 2.5 Gyr ago, involving substantial decreases in mantle melt fraction in basalts, and in indicators of deep crustal melting and fractionation, such as Na/K, Eu/Eu* (europium anomaly) and La/Yb ratios in felsic rocks. Along with an increase in preserved crustal thickness across the Archaean/Proterozoic boundary, these data are consistent with a model in which high-degree Archaean mantle melting produced a thick, mafic lower crust and consequent deep crustal delamination and melting--leading to abundant tonalite-trondhjemite-granodiorite magmatism and a thin preserved Archaean crust. The coincidence of the observed changes in geochemistry and crustal thickness with stepwise atmospheric oxidation at the end of the Archaean eon provides a significant temporal link between deep Earth geochemical processes and the rise of atmospheric oxygen on the Earth.
Temporal correlation between some continental flood basalt eruptions and mass extinctions has been proposed to indicate causality, with eruptive volatile release driving environmental degradation and ...extinction. We tested this model for the Deccan Traps flood basalt province, which, along with the Chicxulub bolide impact, is implicated in the Cretaceous-Paleogene (K-Pg) extinction approximately 66 million years ago. We estimated Deccan eruption rates with uranium-lead (U-Pb) zircon geochronology and resolved four high-volume eruptive periods. According to this model, maximum eruption rates occurred before and after the K-Pg extinction, with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction. These findings support extinction models that incorporate both catastrophic events as drivers of environmental deterioration associated with the K-Pg extinction and its aftermath.
Endothelial nitric oxide synthase (eNOS, NOS3) is responsible for producing nitric oxide (NO)—a key molecule that can directly (or indirectly) act as a vasodilator and anti-inflammatory mediator. In ...this review, we examine the structural effects of regulation of the eNOS enzyme, including post-translational modifications and subcellular localization. After production, NO diffuses to surrounding cells with a variety of effects. We focus on the physiological role of NO and NO-derived molecules, including microvascular effects on vessel tone and immune response. Regulation of eNOS and NO action is complicated; we address endogenous and exogenous mechanisms of NO regulation with a discussion of pharmacological agents used in clinical and laboratory settings and a proposed role for eNOS in circulating red blood cells.
In this article, the Kocks-Mecking formalism is employed to analyze the grain size and thickness effects which modify the mechanical behavior of nickel polycrystals. To this aim, a two-internal ...variable Kocks-Mecking model, based on the evolution of forest and mobile dislocation densities, is numerically optimized using a wide experimental database of tensile curves of nickel polycrystals already published. The original model has been modified to take into account the grain size contribution to strain hardening in addition to the conventional dislocation production and annihilation terms. Using this improved model, the tensile curves of samples with different grain sizes, thicknesses and number of grains across the thickness are well reproduced. By means of an analysis of the model parameters, i.e. dislocation mean free path, cross-slip rate and dislocation densities, the strain mechanisms of nickel polycrystals are investigated as a function of their microstructural characteristics. For specimens with few grains across the thickness, the rate of dislocation annihilation is increased which, in turn, decreases the forest dislocation density and stress level. These results show, first, that the well-known Kocks-Mecking model is able to reproduce size effect and, second, confirm previous assumptions about the mechanical behavior of miniaturized samples. Eventually, the modeling of the mechanical behavior for samples concerned by miniaturization taking into account the surface effect contribution is discussed.
•The Kocks-Mecking-Estrin model is modified to take into account the size effects.•Grain size and thickness effects are well predicted by the model for Ni polycrystals.•Dislocation density predictions are coherent with crystalline plasticity model ones.•Dislocation mean free path prediction is compared to dislocation cell measurements.
Recent clinical evidence identified anemia to be correlated with severe complications of cardiovascular disease (CVD) such as bleeding, thromboembolic events, stroke, hypertension, arrhythmias, and ...inflammation, particularly in elderly patients. The underlying mechanisms of these complications are largely unidentified. Recent Advances: Previously, red blood cells (RBCs) were considered exclusively as transporters of oxygen and nutrients to the tissues. More recent experimental evidence indicates that RBCs are important interorgan communication systems with additional functions, including participation in control of systemic nitric oxide metabolism, redox regulation, blood rheology, and viscosity. In this article, we aim to revise and discuss the potential impact of these noncanonical functions of RBCs and their dysfunction in the cardiovascular system and in anemia.
The mechanistic links between changes of RBC functional properties and cardiovascular complications related to anemia have not been untangled so far.
To allow a better understanding of the complications associated with anemia in CVD, basic and translational science studies should be focused on identifying the role of noncanonical functions of RBCs in the cardiovascular system and on defining intrinsic and/or systemic dysfunction of RBCs in anemia and its relationship to CVD both in animal models and clinical settings. Antioxid. Redox Signal. 26, 718-742.
The oxygenation of the deep ocean in the geological past has been associated with a rise in the partial pressure of atmospheric molecular oxygen (O2) to near-present levels and the emergence of ...modern marine biogeochemical cycles. It has also been linked to the origination and diversification of early animals. It is generally thought that the deep ocean was largely anoxic from about 2,500 to 800 million years ago, with estimates of the occurrence of deep-ocean oxygenation and the linked increase in the partial pressure of atmospheric oxygen to levels sufficient for this oxygenation ranging from about 800 to 400 million years ago. Deep-ocean dissolved oxygen concentrations over this interval are typically estimated using geochemical signatures preserved in ancient continental shelf or slope sediments, which only indirectly reflect the geochemical state of the deep ocean. Here we present a record that more directly reflects deep-ocean oxygen concentrations, based on the ratio of Fe3+ to total Fe in hydrothermally altered basalts formed in ocean basins. Our data allow for quantitative estimates of deep-ocean dissolved oxygen concentrations from 3.5 billion years ago to 14 million years ago and suggest that deep-ocean oxygenation occurred in the Phanerozoic (541 million years ago to the present) and potentially not until the late Palaeozoic (less than 420 million years ago).
Gene-by-environment interaction (G×E) studies in psychiatry have typically been conducted using a candidate G×E (cG×E) approach, analogous to the candidate gene association approach used to test ...genetic main effects. Such cG×E research has received widespread attention and acclaim, yet cG×E findings remain controversial. The authors examined whether the many positive cG×E findings reported in the psychiatric literature were robust or if, in aggregate, cG×E findings were consistent with the existence of publication bias, low statistical power, and a high false discovery rate.
The authors conducted analyses on data extracted from all published studies (103 studies) from the first decade (2000-2009) of cG×E research in psychiatry.
Ninety-six percent of novel cG×E studies were significant compared with 27% of replication attempts. These findings are consistent with the existence of publication bias among novel cG×E studies, making cG×E hypotheses appear more robust than they actually are. There also appears to be publication bias among replication attempts because positive replication attempts had smaller average sample sizes than negative ones. Power calculations using observed sample sizes suggest that cG×E studies are underpowered. Low power along with the likely low prior probability of a given cG×E hypothesis being true suggests that most or even all positive cG×E findings represent type I errors.
In this new era of big data and small effects, a recalibration of views about groundbreaking findings is necessary. Well-powered direct replications deserve more attention than novel cG×E findings and indirect replications.
In terrestrial ecosystems, vascular plants photosynthesize and respire to produce organic matter and CO₂, respectively. Fractions of these products dissolve and are processed belowground to become ...dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) for export in landscape drainage to receiving inland waters. This paper gathers findings from across the Earth and ecological sciences to assemble a simple framework explaining the interplay among these processes in the critical zone (CZ), the skin of Earth from the top of the vegetation canopy through soil and subsoil to the base of active groundwater circulation. In this framework, chemical weathering, that is the dissolution of soil and subsoil mineral material, is a keystone process fueling carbon and energy flow through the system. The ecologic function of weathering dynamically generates nutrients positively feeding back into biosynthesis (and DOC generation) supporting heterotrophy. Root and heterotrophic respiration in turn drive the geologic function of weathering, entraining and stabilizing CO₂ in solution (DIC generation) for storage in the hydrosphere and lithosphere. The CZ framework supports straight-forward explanations of spatiotemporal patterns of DOC and DIC exports from catchments, including how they differentially respond to hydrologic and ecosystem development dynamics. Mechanisms that generate and export dissolved C also fuel and affect dynamics of stream emission of CO₂ to the atmosphere. At larger time scales, terrestrial C-export rates and dynamics co-evolve with CZ development and disturbance. Ultimately terrestrial C exports are plate-tectonically and thermostatically capped and floored by volcanic CO₂ production and carbonate chemistry in Earth’s crust.
The end-Cretaceous mass extinction was marked by both the Chicxulub impact and the ongoing emplacement of the Deccan Traps flood basalt province. To understand the mechanism of extinction, we must ...disentangle the timing, duration, and intensity of volcanic and meteoritic environmental forcings. In this study, we used a parallel Markov chain Monte Carlo approach to invert for carbon dioxide (CO
2
) and sulfur dioxide (SO
2
) emissions, export productivity, and remineralization from 67 to 65 million years ago using the LOSCAR (Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir) model. Our results closely match observed and proxy data and suggest decoupled CO
2
and SO
2
emissions, a two-step decline in export productivity with a protracted recovery, and no clear volatile impulse at the boundary. More broadly, our methods provide a potential path forward for efficient parallel inversion of complex Earth system models.
Editor’s summary
The end-Cretaceous mass extinction, which included the elimination of all nonavian dinosaurs, occurred after the impact of a meteorite and during a stretch of large-scale volcanism. Although it is known that the impact is temporally linked to the extinction, the relative roles are hard to disentangle. Cox and Keller used an inversion scheme that is agnostic about what occurred geologically but provides best guesses for a number of variables, including carbon and sulfur dioxide release. These gases cause environmental changes, and the results may argue for a two-stage extinction related to the volcanism. This approach should be useful for disentangling other complex events in Earth systems and elsewhere. —Brent Grocholski
Inverse carbon cycle modeling reveals environmental forcings associated with mass extinction.
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