Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary

One or more bolide impacts are hypothesized to have triggered the Younger Dryas cooling at ∼12.9 ka. In support of this hypothesis, varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the Younger Dryas boundary (YDB). We show that bulk sediment and/or magnetic grains/microspherules collected from the YDB sites in Arizona, Michigan, New Mexico, New Jersey, and Ohio have ¹⁸⁷Os/¹⁸⁸Os ratios ≥1.0, similar to average upper continental crust (= 1.3), indicating a terrestrial origin of osmium (Os) in these samples. In contrast, bulk sediments from YDB sites in Belgium and Pennsylvania exhibit ¹⁸⁷Os/¹⁸⁸Os ratios <<1.0 and at face value suggest mixing with extraterrestrial Os with ¹⁸⁷Os/¹⁸⁸Os of ∼0.13. However, the Os concentration in bulk sample and magnetic grains from Belgium is 2.8 pg/g and 15 pg/g, respectively, much lower than that in average upper continental crust (=31 pg/g), indicating no meteoritic contribution. The YDB site in Pennsylvania is remarkable in yielding 2- to 5-mm diameter spherules containing minerals such as suessite (Fe-Ni silicide) that form at temperatures in excess of 2000 °C. Gross texture, mineralogy, and age of the spherules appear consistent with their formation as ejecta from an impact 12.9 ka ago. The ¹⁸⁷Os/¹⁸⁸Os ratios of the spherules and their leachates are often low, but Os in these objects is likely terrestrially derived. The rare earth element patterns and Sr and Nd isotopes of the spherules indicate that their source lies in 1.5-Ga Quebecia terrain in the Grenville Province of northeastern North America.The Younger Dryas (YD) event represents a major cooling interlude during the last deglaciation between 12.9 and 11.6 ka and is widely recorded over the mid- to high latitudes in the Northern Hemisphere with associated perturbations in the tropical regions. The abrupt onset of this event appears to have coincided with the Pleistocene megafaunal extinction in North America and Europe (1) and Clovis Paleoindian cultural modifications and population declines (2, 3). The prevalent postulated mechanism for the YD cooling is meltwater flooding and iceberg calving that released fresh water into the northeast Atlantic and/or the Arctic Oceans (4–7), resulting in a temporary shutdown of meridional overturning circulation (8). Recent modeling work (9) has added support to the idea that flooding of the Arctic via the McKenzie River could provide the “freshwater cap” that inhibited open-ocean deep convection.Firestone et al. (10) proposed an alternate hypothesis that the cooling was directly or indirectly triggered by one or more cosmic airbursts or impacts that engendered enormous environmental and biotic changes. In support of this hypothesis, they reported extraterrestrial (ET) signatures from 12 sites dating to the Younger Dryas boundary (YDB) at ∼12.9 ka (10). The ET evidence from these sites is sometimes associated with a black layer (or black mat), which is also found at about 70 Clovis-age archaeological sites (1). Directly beneath the black mat is the YDB, a relatively thin layer, which is reported to exhibit variable enrichment in Ir (10). Firestone et al. (10) also found the YDB layer to be enriched in magnetic grains with variable amounts of Ir, magnetic microspherules, fullerenes containing ET ³He, charcoal, soot, carbon spherules, and glass-like carbon. The impact hypothesis was further supported and extended by Kennett et al. (11), who reported nanodiamonds formed at high pressure at the YDB. The hypothesis is controversial, however, in part because other investigators have suggested alternate scenarios to explain the above evidential markers (12–15).To date, 184 confirmed impact structures have been identified around the world (Earth Impact Database: www.passc.net/EarthImpactDatabase/index.html). Crater structure, shock metamorphism, and a meteoritic contribution are important markers used to confirm an impact structure (16–18). However, a visible crater, breccias, and high-pressure–modified minerals remain unreported for the YDB horizon, with the exception of possibly shock-synthesized hexagonal nanodiamonds (11, 19), an observation disputed by Daulton and coworkers (12, 15).The proponents of the YDB impact hypothesis have pointed out, however, the lack of traditional impact markers in a number of widely accepted impact events (e.g., Australasian tektites, Libyan Desert glass, the Tunguska event), all suggested to have resulted from non-crater–producing airbursts (19, 20). Thus, a lack of traditional markers at the YDB may possibly be the result of one or more impactors exploding in the atmosphere or striking the Laurentide Ice Sheet (10). Recently, a submerged 4-km-wide candidate impact crater (Corossol Crater) has been discovered in the Sept Iles, Gulf of St. Lawrence, Canada and has been provisionally dated to 12.9 ka.^† Two other features, one (Charity Shoal) submerged in Lake Ontario (21) and the other (Bloody Creek) in Nova Scotia (22), may represent additional or alternate impact craters associated with the YDB event. They have not been accurately dated, but their proposed range of dates spans the YD onset.A key piece of evidence reported by Firestone et al. (10) is that of anomalously high concentrations of magnetic spherules with diameters ranging from 10 to 150 μm and magnetic grains at the YDB. Magnetic grains at several YDB sites were reported to be enriched in Ir but inferred to show a nugget effect as sometimes Ir enrichment could not be reproduced (10). The concentrations of magnetic spherules reported by Firestone et al. (10) have been confirmed by seven independent groups (20, 23) from YDB sites in Venezuela (24), Arizona (25), New Mexico, South Carolina, and Maryland (26). Another study by Surovell et al. (27) was unable to replicate either the abundances or the chronostratigraphy of the magnetic spherules reported by Firestone et al. (10). That finding, however, has been contradicted by LeCompte et al. (26), who found magnetic spherules in three sites examined by Surovell et al. (27).Studies investigating Ir enrichment in bulk sediment have also produced conflicting results. Paquay et al. (28) could not replicate the high values of Ir reported by Firestone et al. (10) at a number of locations, including Murray Springs, AZ. In contrast, Haynes et al. (29) found extremely high Ir concentrations in the YDB magnetic fraction (72 ng/g) at Murray Springs. This value is substantially higher than the 2.25 ng/g of Ir reported by Firestone et al. (10) in bulk sediment and is >3,000 times crustal abundance, exceeding concentrations found in most meteorites and impact craters. Similarly, anomalous enrichments in rare earth elements (REE) and high concentrations of both osmium (Os) and Ir in YDB sediments from Murray Springs and Lommel (Belgium) have been reported.^‡ Likewise, Ir enrichments in the YDB layer in southwest England have been reported.^§ Thus, some independent groups have confirmed YDB Ir anomalies, whereas others have not.Although anomalously high concentrations of Ir are considered to be indicators of meteoritic influxes during an ET impact on Earth (30), high Ir concentrations alone are insufficient to prove an ET contribution as they can also result from terrestrial processes. Turekian (31) argued that Os concentrations and isotope measurements should be used to detect the existence of an ET component. Being a platinum group element (PGE), Os is highly enriched in meteorites/cosmic dust and depleted in the upper continental crust. The average Os/Ir ratios of meteorites and for the upper continental crust are 1.1 and 1.4, respectively (see compilation in ref. 32), implying little fractionation between these elements during continental crust formation. In contrast, the Os/Ir ratio in sediments is quite variable due to the differences in redox behavior of these elements. Thus, the Os/Ir ratio of organic rich black shale and pelagic carbonates (= 3–5) is much higher than that of Fe-Mn nodules/crusts and pelagic sediment (= 0.2–0.4) (32).A difference in Os isotopic composition between meteorites and continental crustal rocks, however, makes Os isotopes a highly sensitive tracer of extraterrestrial material. Radiogenic ¹⁸⁷Os is produced from β-decay of ¹⁸⁷Re with a half-life of 42 Ga. The Os isotope ratio (¹⁸⁷Os with respect to stable and nonradiogenic isotope ¹⁸⁸Os) of various terrestrial and ET materials is thus a reflection of their Re/Os ratio and time elapsed after their formation from a primitive source. On average, ¹⁸⁷Os/¹⁸⁸Os ratios of meteorites/cosmic dust range from 0.117 to 0.128 and are similar to the primitive upper mantle (0.129 with ¹⁸⁷Re/¹⁸⁸Os = 0.36). In comparison, average ¹⁸⁷Os/¹⁸⁸Os ratio of the upper continental crust is approximately 10 times higher (1.26 with ¹⁸⁷Re/¹⁸⁸Os = 48). The Os concentration of meteorites is variable with ordinary and carbonaceous meteorites and cosmic dust ranging from 0.6 to 1 μg/g and iron meteorites ∼30 μg/g (see compilation in ref. 32). In comparison, the Os concentration of terrestrial samples is from 3 ng/g (mantle peridotite) to 10–50 pg/g (loess samples representing average upper continental crust). Low ¹⁸⁷Os/¹⁸⁸Os ratio and high Os concentration in ET material provide a substantial contrast to the upper continental material with high ¹⁸⁷Os/¹⁸⁸Os ratio and extremely low Os concentrations. Thus, ¹⁸⁷Os/¹⁸⁸Os ratios combined with Os concentrations are a robust analytical approach to determine ET contribution in samples. A number of investigations have used Os isotope composition to trace meteorite impacts throughout geological time and to determine the extent to which the meteorite component is present in target rocks or in distal ejecta (e.g., tektites) from the impact (ref. 32 and references therein).Paquay et al. (28) and others^¶ reported relatively high ¹⁸⁷Os/¹⁸⁸Os ratios in the bulk YDB sediments and concluded that PGEs in the YDB horizons in North America and Europe have a terrestrial origin. However, Firestone et al. (10) reported the highest Ir concentrations not in bulk sediments, but rather in the YDB magnetic grains. Moreover, they suggested that the magnetic grains and microspherules recovered from the YDB were most likely ET-impact ejecta. Because microspherules and magnetic grains constitute only a small fraction of YDB sediments (tens to hundreds of thousands of magnetic grains amounting to a few grams per kilogram; e.g., refs. 10, 23, 26), bulk sediment analyses can be expected to overwhelm Ir and Os values imparted by these materials. Consequently, it is essential to determine the Os abundance and isotope composition of magnetic spherules and grains to evaluate the origin and provenance of these objects.Here we examine Os abundance and isotope ratios in YDB bulk sediment samples from six locations, including Blackwater Draw, NM; Sheriden Cave, OH; Murray Springs, AZ; Gainey, MI; Melrose, PA; and Lommel, Belgium. We also investigate magnetic grains for the Gainey and Lommel sites and magnetic microspherule clusters from Newtonville, NJ and Melrose, PA. Finally, we examine the origin and provenance of large (2- to 5-mm diameter) spherules from Melrose, using their mineralogy, major element, and REE contents and Os, Nd, and Sr isotope composition. Initial data from this study have been reported previously (^¶, 33). For comparing results from other studies where only Ir is measured, we assume that ET Ir and Os should follow each other with an Os/Ir ratio of 1.1 as fractionation between Os and Ir during an impact is unlikely.     

Intermittent ethanol exposure in adolescent rats: dose-dependent impairments in trace conditioning

BACKGROUND: Recent studies have revealed that the adolescent brain may be especially vulnerable to ethanol-induced toxicity. Corticolimbic regions are more severely damaged following ethanol exposure during adolescence than during adulthood. The consequences of adolescent ethanol exposure on cognition however, have only recently begun to be explored. METHODS: Male and female rats were administered 0, 1.5, 2.5 or 4.5 g/kg ethanol (20% v/v) by acute intragastric gavage during adolescence (postnatal days [PD] 28, 30, 32 and 34). On PD 40, half of the subjects in each dose group were given 5 pairings of a 10-sec flashing light (CS; conditioned stimulus) immediately followed by mild footshock (US; unconditioned stimulus), a procedure known as delay conditioning. The other half were also given 5 CS-US pairings, but the US was presented 10 sec after CS offset, a procedure known as trace conditioning. All subjects were tested for CS-elicited freezing 24 h later. RESULTS: There was no effect of adolescent ethanol exposure on delay conditioned responding, with all subjects demonstrating comparable levels of CS-elicited freezing. In contrast, the amount of freezing in the trace conditioned subjects was negatively correlated with prior ethanol dose. Specifically, exposure to 2.5 or 4.5 g/kg during adolescence resulted in a deficit in trace conditioned responding. CONCLUSIONS: These data indicate that intermittent exposure to ethanol during adolescence results in impairment in hippocampal-dependent trace conditioning that persists beyond the period of ethanol exposure. Delay conditioning was unaffected by prior ethanol treatment, indicating that there was no difficulty in detecting the CS or US, or in the ability to engage in freezing behavior. These results suggest that the adolescent brain may be particularly vulnerable to the effects of repeated exposure to ethanol that can have consequences for nonspatial, hippocampal-dependent cognitive abilities.     

Short-term effects of thrust versus nonthrust mobilization/manipulation directed at the thoracic spine in patients with neck pain: a randomized clinical trial

BACKGROUND AND PURPOSE: Evidence supports the use of manual physical therapy interventions directed at the thoracic spine in patients with neck pain. The purpose of this study was to compare the effectiveness of thoracic spine thrust mobilization/manipulation with that of nonthrust mobilization/manipulation in patients with a primary complaint of mechanical neck pain. The authors also sought to compare the frequencies, durations, and types of side effects between the groups. SUBJECTS: The subjects in this study were 60 patients who were 18 to 60 years of age and had a primary complaint of neck pain. METHODS: For all subjects, a standardized history and a physical examination were obtained. Self-report outcome measures included the Neck Disability Index (NDI), a pain diagram, the Numeric Pain Rating Scale (NPRS), and the Fear-Avoidance Beliefs Questionnaire. After the baseline evaluation, the subjects were randomly assigned to receive either thoracic spine thrust or nonthrust mobilization/manipulation. The subjects were reexamined 2 to 4 days after the initial examination, and they again completed the NDI and the NPRS, as well as the Global Rating of Change (GROC) Scale. The primary aim was examined with a 2-way repeated-measures analysis of variance (ANOVA), with intervention group (thrust versus nonthrust mobilization/manipulation) as the between-subjects variable and time (baseline and 48 hours) as the within-subject variable. Separate ANOVAs were performed for each dependent variable: disability (NDI) and pain (NPRS). For each ANOVA, the hypothesis of interest was the 2-way group x time interaction. RESULTS: Sixty patients with a mean age of 43.3 years (SD=12.7) (55% female) satisfied the eligibility criteria and agreed to participate in the study. Subjects who received thrust mobilization/manipulation experienced greater reductions in disability, with a between-group difference of 10% (95% confidence interval [CI]=5.3-14.7), and in pain, with a between-group difference of 2.0 (95% CI=1.4-2.7). Subjects in the thrust mobilization/manipulation group exhibited significantly higher scores on the GROC Scale at the time of follow-up. No differences in the frequencies, durations, and types of side effects existed between the groups. DISCUSSION AND CONCLUSION: The results suggest that thoracic spine thrust mobilization/manipulation results in significantly greater short-term reductions in pain and disability than does thoracic nonthrust mobilization/manipulation in people with neck pain.     

A novel treatment for plantar ulcers in leprosy: local superficial flaps

Plantar ulceration is the most common serious disability occurring in patients of leprosy. Growth and emergence of innovative procedures in plastic surgery has greatly revolutionized the treatment of this highly frustrating problem. In the present study, a total of 40 leprosy patients were included. These ulcers were managed using different types of local superficial flaps (advancement, rotation, transposition and first toe web flap). Majority of ulcers healed within 4 weeks and patients were discharged within 6-8 weeks postoperatively. Patients were followed up for a period of 6 months to 3 years. Ulcers recurred in only 25% of all the ulcers operated upon and we observed that management of plantar ulcers by using appropriate local superficial plantar flaps is a viable option and worth trying in view of low incidence of recurrence and relatively shorter duration of hospital stay.     

Location-specific strategies for eliminating US national racial-ethnic [... formula ...] exposure inequality

Air pollution levels in the United States have decreased dramatically over the past decades, yet national racial-ethnic exposure disparities persist. For ambient fine particulate matter (PM2.5), we investigate three emission-reduction approaches and compare their optimal ability to address two goals: 1) reduce the overall population average exposure (“overall average”) and 2) reduce the difference in the average exposure for the most exposed racial-ethnic group versus for the overall population (“national inequalities”). We show that national inequalities in exposure can be eliminated with minor emission reductions (optimal: ~1% of total emissions) if they target specific locations. In contrast, achieving that outcome using existing regulatory strategies would require eliminating essentially all emissions (if targeting specific economic sectors) or is not possible (if requiring urban regions to meet concentration standards). Lastly, we do not find a trade-off between the two goals (i.e., reducing overall average and reducing national inequalities); rather, the approach that does the best for reducing national inequalities (i.e., location-specific strategies) also does as well as or better than the other two approaches (i.e., sector-specific and meeting concentration standards) for reducing overall averages. Overall, our findings suggest that incorporating location-specific emissions reductions into the US air quality regulatory framework 1) is crucial for eliminating long-standing national average exposure disparities by race-ethnicity and 2) can benefit overall average exposures as much as or more than the sector-specific and concentration-standards approaches.

The Clean Air Act has dramatically reduced outdoor air pollution levels in the United States, with (during 1990 through 2020) aggregate benefits exceeding costs 30-to-1 ($2 trillion versus $65 billion) (1). Important regulatory strategies include the National Ambient Air Quality Standards (NAAQS) and sector-specific emission-reduction technology requirements (e.g., Best Achievable Control Technology [BACT] standards). However, exposure inequalities persist (2–7). Disparities by race-ethnicity are larger than, and distinct from, those by income (4–6, 8, 9). Racial-ethnic inequalities in US ambient air pollution and subsequent exposures are attributable in part to racist planning, including historical, race-based housing segregation and land-use practices (10–18). Environmental racism scholars have suggested that strategies and policies for eliminating disparities will be most effective when racial-ethnic injustices are centered and directly addressed (19–22).The existing literature documents exposure inequities (3–7, 9, 23–26) and investigates the impacts on inequities of emission changes for specific sources (e.g., refs. 27–36) or locations (37–43). However, the scientific literature has not investigated how to eliminate national racial-ethnic inequalities in air pollution or what level of emission reduction would be required to do so (44).We examine three potential approaches to reduce or eliminate national exposure inequalities: 1) location-specific emission reductions (hereafter, “location”), 2) sector-specific emission reductions (“sector”; analogous to BACT-type approaches), and 3) requiring regions to meet a concentration standard (“NAAQS-like”). Approaches 2 and 3 mirror aspects of current regulations; approach 1 would be a new regulatory approach. We find that the location approach is by far the most effective (can eliminate national disparities with only small absolute emission reductions); the sector approach is poor (can reduce disparities, but requires substantially larger emission reductions; cannot eliminate disparities except by eliminating nearly all emissions); and NAAQS-like is the least effective (does not eliminate disparities). The location approach is also the strongest of the three for reducing population-average exposures.To quantitatively compare the three approaches, we use the publicly available InMAP (Intervention Model for Air Pollution) source-receptor matrix (ISRM) (45) to estimate long-term average ambient fine particulate matter (PM2.5) concentrations across the contiguous United States caused by anthropogenic emissions in 2014. Disparity here refers to the difference between population-weighted average PM2.5 concentrations for the most exposed racial-ethnic group minus the overall population (in sensitivity analyses, we instead investigate government-designated “high vulnerability” [HV] locations; Materials and Methods). ISRM predicts the concentration of primary PM2.5 and secondary PM2.5 formed from nitrogen oxides (NOx), sulfur oxides (SOx), ammonia (NH3), and volatile organic compounds (VOCs). We employ the 2014 US Environmental Protection Agency (EPA) National Emission Inventory, grouped into 14 source sectors (see Fig. 2B, SI Appendix, and below). ISRM contains 52,411 grid cells (locations) with size (i.e., spatial resolution) ranging from 1 km in densely populated urban centers to 48 km in sparsely populated rural areas; the average spatial resolution is 2.6 km in Urban Areas and 22.6 km in non-Urban Areas (13.2 km overall). Emissions reductions for location and sector are an optimization to maximally reduce disparities for the most exposed group relative to the overall population average. They use the spatial resolution of the simulation grid and the 14 source sectors, respectively. Thus, our results inform what that method could optimally do to reduce or eliminate racial-ethnic exposure disparities. The NAAQS-like approach simulates successive, proportional emission reductions in each region violating the hypothetical NAAQS (e.g., 6 µg/m3), until the NAAQS-like standard is met.Open in a separate windowFig. 2.Emission reductions for the three approaches: by location (i.e., corresponding to the green lines, Fig. 1) (A), by sector (corresponding to blue lines, Fig. 1) (B), and NAAQS-like (orange lines, Fig. 1) (C). A displays national results (Left) and zoomed-in results for 10 large areas (Right). Spatial units displayed in C are CBSAs, the geographic unit for NAAQS evaluation. The three approaches offer fundamentally different ways of formulating and prioritizing emission reductions. Ag., agriculture; Const., construction; Elec., electricity; HD, heavy duty; LD, light duty; Misc., miscellaneous; Res., residential; Veh., vehicle.     

Echocardiographic assessment of left ventricular diastolic function and filling pressure in atrial fibrillation

Diastolic dysfunction has been linked to 2 epidemics: atrial fibrillation (AF) and heart failure. The presence and severity of diastolic dysfunction are associated with an increased risk for first AF and first heart failure in patients with sinus rhythm. Furthermore, the risk for heart failure is markedly increased once AF develops. The evaluation of diastolic function once AF has developed remains a clinical challenge. The conventional use of Doppler echocardiography for the assessment and grading of diastolic dysfunction relies heavily on evaluating the relation of ventricular and atrial flow characteristics. The mechanical impairment of the left atrium and the variable cycle lengths in AF render the evaluation of diastolic function difficult. A few Doppler echocardiographic methods have been proved clinically useful for the estimation of diastolic left ventricular filling pressures in AF, but these appear to be underutilized. Several innovative methods are emerging that promise to provide greater precision in diastolic function assessment, but their clinical utility in AF remains to be established. In conclusion, this review provides an up-to-date discussion of the evaluation of diastolic function assessment in AF and how it may be important in the clinical management of patients with AF.     

Role for Streptococcal Collagen-Like Protein 1 in M1T1 Group A Streptococcus Resistance to Neutrophil Extracellular Traps

Streptococcal collagen-like protein 1 (Scl-1) is one of the most highly expressed proteins in the invasive M1T1 serotype group A Streptococcus (GAS), a globally disseminated clone associated with higher risk of severe invasive infections. Previous studies using recombinant Scl-1 protein suggested a role in cell attachment and binding and inhibition of serum proteins. Here, we studied the contribution of Scl-1 to the virulence of the M1T1 clone in the physiological context of the live bacterium by generating an isogenic strain lacking the scl-1 gene. Upon subcutaneous infection in mice, wild-type bacteria induced larger lesions than the Δscl mutant. However, loss of Scl-1 did not alter bacterial adherence to or invasion of skin keratinocytes. We found instead that Scl-1 plays a critical role in GAS resistance to human and murine phagocytic cells, allowing the bacteria to persist at the site of infection. Phenotypic analyses demonstrated that Scl-1 mediates bacterial survival in neutrophil extracellular traps (NETs) and protects GAS from antimicrobial peptides found within the NETs. Additionally, Scl-1 interferes with myeloperoxidase (MPO) release, a prerequisite for NET production, thereby suppressing NET formation. We conclude that Scl-1 is a virulence determinant in the M1T1 GAS clone, allowing GAS to subvert innate immune functions that are critical in clearing bacterial infections.     

Awareness of illness and nonadherence to antipsychotic medications among persons with schizophrenia

OBJECTIVE: The purpose of this study was to assess the effects of patients' awareness of their illness on the clinical presentation, management, and course of nonadherence to antipsychotic medications among patients with schizophrenia. METHODS: A national survey was conducted of psychiatrists who were treating patients with schizophrenia. The survey was sent to 771 psychiatrists, of whom 534 responded, for a response rate of 69 percent. The psychiatrists were asked to report on presentation, management, and course for one adult patient with schizophrenia who had been under their care for at least one year and who had been nonadherent to oral antipsychotics at some point in the past year. Patients who were aware that they had a mental illness were compared with those who were not aware. RESULTS: Of the 534 respondent psychiatrists, 310 reported on an eligible patient, and 300 of these patients were classified by illness awareness. Ninety-seven patients, or 32 percent, were not aware that they had a mental illness. These patients who lacked awareness had significantly longer episodes of antipsychotic nonadherence, were more likely to completely cease taking the antipsychotic medication, were more likely to have severe positive symptoms, and were more likely to be psychiatrically hospitalized after nonadherence than those who were aware of their illness. Psychological interventions and several types of family interventions were significantly less effective among patients who lacked awareness. CONCLUSIONS: A lack of awareness of mental illness is common among patients with schizophrenia who are nonadherent to antipsychotics. Such nonadherence tends to be especially disruptive and unresponsive to simple commonly used psychological interventions.