Trace element geochemistry of K-rich impact spherules from howardites

The howardite-eucrite-diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired. The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body

The COMBREX Project: Design, Methodology, and Initial Results

© 2013 Brian P. et al.Prior to the “genomic era,” when the acquisition of DNA sequence involved significant labor and expense, the sequencing of genes was strongly linked to the experimental characterization of their products. Sequencing at that time directly resulted from the need to understand an experimentally determined phenotype or biochemical activity. Now that DNA sequencing has become orders of magnitude faster and less expensive, focus has shifted to sequencing entire genomes. Since biochemistry and genetics have not, by and large, enjoyed the same improvement of scale, public sequence repositories now predominantly contain putative protein sequences for which there is no direct experimental evidence of function. Computational approaches attempt to leverage evidence associated with the ever-smaller fraction of experimentally analyzed proteins to predict function for these putative proteins. Maximizing our understanding of function over the universe of proteins in toto requires not only robust computational methods of inference but also a judicious allocation of experimental resources, focusing on proteins whose experimental characterization will maximize the number and accuracy of follow-on predictions.COMBREX is funded by a GO grant from the National Institute of General Medical Sciences (NIGMS) (1RC2GM092602-01).Peer Reviewe

Geochemistry of the Martian meteorite ALH 84001, revisited

International audienceMajor and trace element abundances were determined on powders prepared from four distinct chips from Allan Hills (ALH) 84001 to constrain the bulk rock composition, and to assess the trace element abundances of orthopyroxenes and phosphates. Our new determinations were used to evaluate the composition of the parental melt of this stone. An unrealistic light rare earth element (REE)-enriched parental melt is calculated from the composition of the orthopyroxene and relevant equilibrium partition coefficients. The involvement of a small amount of trapped melt and subsolidus reequilibrations between orthopyroxene and the interstitial phases can account for this discrepancy. A parental melt that displays a trace element pattern (REE, Zr, and Hf) that closely resembles enriched shergottites such as Zagami or Los Angeles is calculated if these effects are taken into account. These results suggest that some shergottitic melts were already erupted on Mars during the Noachian

The Use of Environmental Justice Screening Tool and Self-Reported Data to Inform Pregnancy and Birth Outcomes in a Population of Central Ohio Deliveries

El estudio es el resultado de una investigación cualitativa realizada con un grupo de profesores y profesoras que imparten clases de historia en centros de educación secundaria de Chile, que indaga en sus ideas sobre qué puede aportar la enseñanza de la historia al desarrollo del pensamiento crítico de los estudiantes. La información obtenida a través de cuestionarios, entrevistas y análisis curricular evidencia que los docentes consideran el pensamiento crítico como un proceso continuo de desarrollo de habilidades intelectuales, sociales e históricas. El profesorado también considera que el pensamiento crítico debe enseñar a los estudiantes a pensar y actuar de manera razonada y autónoma frente a situaciones de su entorno social. El desarrollo de habilidades intelectuales y sociales puede ser abordado desde cualquier disciplina, pero la historia escolar tiene un papel fundamental en la formación del pensamiento crítico. Los docentes son conscientes de esta realidad, pero no siempre realizan una enseñanza que forme el pensamiento histórico y ayude al alumnado a desarrollar una conciencia histórica, que es la aportación más relevante de la enseñanza de la historia a la formación del pensamiento críticoThe study is the result of a qualitative research carried out with a group of teachers who teach history classes in secondary education centers in Chile, who investigates in their ideas on what can teaching history teaching to the development of thought critical of students. The information obtained through questionnaires, interviews and curricular analysis shows that teachers consider critical thinking as a continuous process of developing intellectual, social and historical skills. Teachers also believe that critical thinking should teach students to think and act in a reasoned and autonomous way in the face of situations in their social environment. The development of intellectual and social skills can be approached from any discipline, but the school history plays a fundamental role in the formation of critical thinking. Teachers are aware of this reality, but do not always carry out a teaching that shapes historical thinking and helps students to develop a historical awareness, which is the most relevant contribution of teaching history to the formation of critical thinkin

Determination of rare earth elements and other trace elements (Y, Mn, Co, Cr) in seawater using Tm addition and Mg(OH)2 co-precipitation

International audienceThis paper reports on a novel procedure for determining trace element abundances (REE and Y, Cr, Mn, Co) in seawater by inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The procedure uses a combination of pre-concentration using co-precipitation onto magnesium hydroxides and addition of thulium spike. The validity of the method was assessed onto 25 ml volumes of certified reference materials (NASS- and CASS-4) and in house seawater standard. Procedural blanks were determined by applying the same procedure to aliquots of seawater previously depleted in trace elements by successive Mg(OH)2 co-precipitations, yielding estimated contributions to the studied samples better than 1.1% for all elements, with the exception of Cr (<3.3%) and Co (up to 8%). The reproducibility of the method over the six month duration of the study was smaller than 11% RSD for all the studied elements. Results obtained for NASS-5 and CASS-4 agree well with published working values for trace elements

Relative chronology of crust formation on asteroid Vesta: Insights from the geochemistry of diogenites

International audienceThe eucrites and diogenites are meteorites that probably originate from asteroid 4-Vesta. The upper part of the crust of this body is certainly composed of eucrites which are basaltic or gabbroic rocks. Diogenites are ultramafic cumulates whose relationships with eucritic lithologies are unknown. Here, we show that the orthopyroxenes of some diogenites display very deep negative Eu anomalies (Eu/Eu* close to 0.1 or lower). The contamination of the parental magmas of diogenites by melts derived by partial melting of the eucritic crust can satisfactorily explain the range of the Eu anomalies displayed by diogenites. Thus, these anomalies are the first firm indication that parental melts of diogenites have intruded the eucritic crust, and consequently are younger than eucrites

Geochemistry of CI chondrites: Major and trace elements, and Cu and Zn Isotopes

International audienceIn order to check the heterogeneity of the CI chondrites and determine the average composition of this group of meteorites, we analyzed a series of six large chips (weighing between 0.6 and 1.2 g) of Orgueil prepared from five different stones. In addition, one sample from each of Ivuna and Alais was analyzed. Although the sizes of the chips used in this study were "large", our results show evidence for minor chemical heterogeneity in Orgueil, particularly for alkali elements and U. After removal of one outlier sample, the spread of the results is considerably reduced. For most of the 46 elements analyzed in this study, the average composition calculated for Orgueil is in very good agreement with previous CI estimates. This average, obtained with a "large" mass of samples, is analytically homogeneous and is suitable for normalization purposes. Finally, the Cu and Zn isotopic ratios are homogeneously distributed within the CI parent body with a spread of less than 100 ppm per atomic mass unit (amu)