Project description:The absence of crustal magnetic fields above the martian basins Hellas, Argyre, and Isidis is often interpreted as proof of an early, before 4.1 billion years (Ga) ago, or late, after 3.9 Ga ago, dynamo. We revisit these interpretations using new MAVEN magnetic field data. Weak fields are present over the 4.5-Ga old Borealis basin, with the transition to strong fields correlated with the basin edge. Magnetic fields, confined to a near-surface layer, are also detected above the 3.7-Ga old Lucus Planum. We conclude that a dynamo was present both before and after the formation of the basins Hellas, Utopia, Argyre, and Isidis. A long-lived, Earth-like dynamo is consistent with the absence of magnetization within large basins if the impacts excavated large portions of strongly magnetic crust and exposed deeper material with lower concentrations of magnetic minerals.
Project description:The continental crust is a major geochemical reservoir, the evolution of which has shaped the surface environment of Earth. In this study, we present a new model of coupled crust-mantle-atmosphere evolution to constrain the growth of continental crust with atmospheric 40Ar/36Ar. Our model is the first to combine argon degassing with the thermal evolution of Earth in a self-consistent manner and to incorporate the effect of crustal recycling and reworking using the distributions of crustal formation and surface ages. Our results suggest that the history of argon degassing favors rapid crustal growth during the early Earth. The mass of continental crust, highly enriched in potassium, is estimated to have already reached >80% of the present-day level during the early Archean. The presence of such potassium-rich, likely felsic, crust has important implications for tectonics, surface environment, and the regime of mantle convection in the early Earth.
Project description:Multiple sclerosis (MS) is a progressive disease characterized by widespread white matter lesions in the brain and spinal cord. In addition to well-characterized motor deficits, MS results in cognitive impairments in several domains, notably in episodic autobiographical memory. Recent studies have also revealed that patients with MS exhibit deficits in episodic future thinking, i.e., our capacity to imagine possible events that may occur in our personal future. Both episodic memory and episodic future thinking have been shown to share cognitive and neural mechanisms with a related kind of hypothetical simulation known as episodic counterfactual thinking: our capacity to imagine alternative ways in which past personal events could have occurred but did not. However, the extent to which episodic counterfactual thinking is affected in MS is still unknown. The current study sought to explore this issue by comparing performance in mental simulation tasks involving either past, future or counterfactual thoughts in relapsing-remitting MS. Diffusion weighted imaging (DWI) measures were also extracted to determine whether changes in structural pathways connecting the brain's default mode network (DMN) would be associated with group differences in task performance. Relative to controls, patients showed marked reductions in the number of internal details across all mental simulations, but no differences in the number of external and semantic-based details. It was also found that, relative to controls, patients with relapsing-remitting MS reported reduced composition ratings for episodic simulations depicting counterfactual events, but not so for actual past or possible future episodes. Additionally, three DWI measures of white matter integrity-fractional anisotropy, radial diffusivity and streamline counts-showed reliable differences between patients with relapsing-remitting MS and matched healthy controls. Importantly, DWI measures associated with reduced white matter integrity in three association tracts on the DMN-the right superior longitudinal fasciculus, the left hippocampal portion of the cingulum and the left inferior longitudinal fasciculus-predicted reductions in the number of internal details during episodic counterfactual simulations. Taken together, these results help to illuminate impairments in episodic simulation in relapsing-remitting MS and show, for the first time, a differential association between white matter integrity and deficits in episodic counterfactual thinking in individuals with relapsing-remitting MS.
Project description:Heavy episodic drinking (HED) can have health and social consequences. This study assesses the associations between HED and demographic, socioeconomic, motivation and effects indicators for people aged 18⁻34 years old living in four cities in different regions of the world. Multistage random sampling was consistent across the four cities (Ilorin (Nigeria), Wuhan (China), Montevideo (Uruguay) and Moscow (Russia)). The questionnaire was forward/back translated and face-to-face interviewing was undertaken. A total of 6235 interviews were undertaken in 2014. Separate univariable and multivariable modelling was undertaken to determine the best predictors of HED. HED prevalence was 9.0%. The best predictors differed for each city. The higher probability of HED in the final models included beliefs that they have reached adulthood, feeling relaxed as an effect of drinking alcohol, and forgetting problems as an effect of drinking alcohol. Lower probability of HED was associated with not being interested in alcohol as a reason for limiting alcohol, and the belief that drinking alcohol is too expensive or a waste of money. Although some indicators were common across the four cities, the variables included in the final models predominantly differed from city to city. The need for country-specific prevention and early intervention programs are warranted.
Project description:People frequently engage in future thinking in everyday life, but it is unknown how simulating an event in advance changes how that event is remembered once it takes place. To initiate study of this important topic, we conducted two experiments in which participants simulated emotional events before learning the hypothetical outcome of each event via narratives. Memory was assessed for emotional details contained in those narratives. Positive simulation resulted in a liberal response bias for positive information and a conservative bias for negative information. Events preceded by positive simulation were considered more favorably in retrospect. In contrast, negative simulation had no impact on subsequent memory. Results were similar across an immediate and delayed memory test and for past and future simulation. These results provide novel insights into the cognitive consequences of episodic future simulation and build on the optimism-bias literature by showing that adopting a favorable outlook results in a rosy memory.
Project description:Fire is a primary mode of natural disturbance in the forests of the Pacific Northwest. Increased fuel loads following fire suppression and the occurrence of several large and severe fires have led to the perception that in many areas there is a greatly increased risk of high-severity fire compared with presettlement forests. To reconstruct the variability of the fire regime in the Siskiyou Mountains, Oregon, we analyzed a 10-m, 2,000-y sediment core for charcoal, pollen, and sedimentological data. The record reveals a highly episodic pattern of fire in which 77% of the 68 charcoal peaks before Euro-American settlement cluster within nine distinct periods marked by a 15-y mean interval. The 11 largest charcoal peaks are significantly related to decadal-scale drought periods and are followed by pulses of minerogenic sediment suggestive of rapid sediment delivery. After logging in the 1950s, sediment load was increased fourfold compared with that from the most severe presettlement fire. Less severe fires, marked by smaller charcoal peaks and no sediment pulses, are not correlated significantly with drought periods. Pollen indicators of closed forests are consistent with fire-free periods of sufficient length to maintain dense forest and indicate a fire-triggered switch to more open conditions during the Medieval Climatic Anomaly. Our results indicate that over millennia fire was more episodic than revealed by nearby shorter tree-ring records and that recent severe fires have precedents during earlier drought episodes but also that sediment loads resulting from logging and road building have no precedent in earlier fire events.
Project description:Many epithermal gold and gold-rich porphyry-type ore deposits are associated with potassic magmas. Hence, potassic magmas are commonly assumed to have been unusually Au-rich or to have contained high Au/Cu ratios. However, these hypotheses remain poorly tested. Here, we report Au concentrations and Au/Cu ratios in silicate melt inclusions analyzed in potassic rocks worldwide. The results suggest that mafic potassic magmas generally contain only 2‒7 ng/g Au, despite common sulfide exhaustion during partial mantle melting. Both the absolute Au concentrations and Au/Cu ratios are comparable to those of mafic calc-alkaline magmas, and they vary little during subsequent magma differentiation because magmatic sulfide precipitation is strongly dominated by monosulfide solid solution that is relatively poor in Au and Cu. We thus suggest that the close association of Au-rich deposits with potassic magmas is not due to Au enrichment in the magma, but rather due to selective Au precipitation at the hydrothermal stage.
Project description:Volcanic eruptions are driven by magma rising through Earth's crust. The style of an eruption depends on intrinsic and extrinsic parameters and is commonly a dynamic process. Thorough and holistic investigation of the related products is key to understanding eruptive phenomena and assessment of volcano-specific hazards. Models of such phenomena are constrained by quantification of the dispersal, the grain size distribution, and pyroclast textures. Pyroclast texture may be described in part by measurements of density and porosity, which depend on pyroclast volume determination. Yet volume determination of irregularly shaped pyroclasts cannot be achieved with geometrical laws, instead necessitating the use of alternative methodologies. Here, we test three methodologies to quantify pyroclast volume on a set of clasts collected from the Minoan eruption deposits from Santorini, Greece. We compare (1) a manual method for obtaining the lengths of three orthogonal axes of the pyroclast with a caliper, (2) an optical method to measure the longest and shortest axes of the pyroclast via multiple photographs, and (3) an Archimedean buoyancy-based method. While the optical and manual methods provide almost identical values of pyroclast volume when tested under laboratory conditions, there is a discrepancy between these two methods and the Archimedean method, which produces an overestimation of ca. 13% in volume. This discrepancy has little impact on the subsequent assessment of porosity and density for which the natural variability of values is observed to be broader. We therefore propose using the manual approach in the field as a simple and fast, yet reliable, method to obtain large volumes of quantitative data on the texture of erupted products, and we also provide a correction factor for in-field volume assessment of rhyodacitic pumices.Supplementary informationThe online version contains supplementary material available at 10.1007/s00445-023-01679-4.
Project description:The Siberian Traps large igneous province (STLIP) is commonly invoked as the primary driver of global environmental changes that triggered the end-Permian mass extinction (EPME). Here, we explore the contributions of coeval felsic volcanism to end-Permian environmental changes. We report evidence of extreme Cu enrichment in the EPME interval in South China. The enrichment is associated with an increase in the light Cu isotope, melt inclusions rich in copper and sulfides, and Hg concentration spikes. The Cu and Hg elemental and isotopic signatures can be linked to S-rich vapor produced by felsic volcanism. We use these previously unknown geochemical data to estimate volcanic SO2 injections and argue that this volcanism would have produced several degrees of rapid cooling before or coincident with the more protracted global warming. Large-scale eruptions near the South China block synchronous with the EPME strengthen the case that the STLIP may not have been the sole trigger.
Project description:Gibberellin (GA) application is routinely used in the table grape industry to increase berry size and cluster length. Although grapevine cultivars show a wide range of growth responsiveness to GA3 application, the reasons for these differences is unclear. To shed light on this issue, two commercial grapevine cultivars with contrasting berry response to GA were selected for comparative analysis, in which we tested if the differences in response: (1) is organ-specific or cultivar-related; (2) will be reflected in qualitative/quantitative differences in transcripts/proteins of central components of GA metabolism and signaling and levels of GA metabolites. Our results showed that in addition to the high response of its berries to GA, internodes and rachis of cv. Black finger (BF) presented a greater growth response compared to that of cv. Spring blush (SB). In agreement, the results exposed significant quantitative differences in GA signaling components in several organs of both cultivars. Exceptionally higher level of all three functional VvDELLA proteins was recorded in young BF organs, accompanied by elevated VvGID1 expression and lower VvSLY1b transcripts. Absence of seed traces, low endogenous GA quantities and lower expression of VvGA20ox4 and VvGA3ox3 were also recorded in berries of BF. Our results raise the hypothesis that, in young organs of BF, low expression of VvSLY1b may be responsible for the massive accumulation of VvDELLA proteins, which then leads to elevated VvGID1 levels. This integrated analysis suggests causal relationship between endogenous mechanisms leading to anomalous GA signaling repression in BF, manifested by high quantities of VvDELLA proteins, and greater growth response to GA application.