Evidences for a Noachian-Hesperian orogeny in Mars

A number of tectonic structures have been located at the Thaumasia Plateau, Daedalia Planum and Aonia Terra, Mars. They include isolated folds with axial traces up to 200 km long, trains of tightly folded structures tens of km long, and thrusts. Their size and geometry are similar to those on Earth, and the direction of compression seems to have varied amply with time, suggesting a complex tectonic evolution. Crater counts on the deformed terrain point to Noachian to Early Hesperian ages. On the basis of the geometry and geological relations of these structures, we propose that they form part of an old martian orogen, the Thaumasia-Aonia Orogen, which embraced not only the Thaumasia Plateau, but areas of Daedalia Planum, Aonia Terra and Nereidum Montes as well. A regional coherent layering is previous to the deformation and could represent the trace of even older stresses on the martian lithosphere.     

WHY WAS HUMBOLDT FORGOTTEN IN THE UNITED STATES?*

ABSTRACT. In the nineteenth century Alexander von Humboldt was acclaimed as “the second Columbus” and “the scientific discoverer of America.” His prestige and fame were such that on 14 September 1869, the hundredth anniversary of his birth, a grand celebration was held with parades, speeches, concerts, and the unveiling of memorials in cities across the country. Humboldt's popularity in the United States endured for the remainder of the nineteenth century, but he dropped from public consciousness in the twentieth century. To account for the eclipse of Humboldt's fame in the United States three hypotheses are discussed: a shift in the character of scientific endeavor; the quality of Humboldt's written work; and the rise of anti‐German sentiment with a concurrent rush to “de‐Germanize” the United States in the early twentieth century.     

The insoluble carbonaceous material of CM chondrites: A possible source of discrete organic compounds under hydrothermal conditions

Abstract— We report on the molecular analyses of the water‐ and solvent‐soluble organic compounds released from the insoluble organic material (IOM) of the Murray meteorite upon treatment with weight‐equivalent amounts of water and under conditions of elevated temperature and pressure. A varied suite of compounds was identified by gas chromatography‐mass spectrometry (GC‐MS). C₃‐C₁₇ alkyl dicarboxylic acids and N‐ and O‐containing hydroaromatic and aromatic compounds were found in the water extracts. The solvent extracts contained N‐, O‐, and S‐containing aromatic compounds, a large number of their isomers and homologs, and a series of polycyclic aromatic hydrocarbons (PAHs) of up to five rings, together with noncondensed aromatic species such as substituted benzenes, biphenyl, and terphenyls as well as their substituted homologs, and hydrated PAHs. Isotopic analyses showed that residue IOMs after hydrothermal treatment had lower deuterium and ¹⁵N content than the untreated material (ΔD = ?833‰ and Δ¹⁵N = ?24.1) but did not differ from it in ¹³C composition. The effect of the hydrothermolytic release was recorded in significant differences between the NMR spectra of untreated and residue IOM. A possible relation to common precursors for the dicarboxylic acids found in the IOM and bulk extracts is discussed.     

The great thickness debate: Ice shell thickness models for Europa and comparisons with estimates based on flexure at ridges

Estimates of the thickness of the ice shell of Europa range from <1 to >30 km. The higher values are generally assumed to be estimates of the entire ice shell thickness, which may include a lower ductile layer of ice, whereas many of the smaller thickness estimates are based on analyses that only consider that portion of the ice layer that behaves elastically at a particular strain rate. One example of the latter is flexure analysis, in which the elastic ice layer is modeled as a plate or sphere that is flexed under the weight of a surface load. We present calculations based on flexure analysis in which we model the elastic ice layer as flexing under a line-load caused by ridges. We use precisely located, parallel flanking cracks as indicators of the location of greatest tensile stress induced by flexure. Our elastic thickness results are spatially variable: ∼500-2200 m (two sites) and ∼200-1000 m (one site). Thorough analysis of Europan flexure studies performed by various researchers shows that the type of model selected causes the greatest variability in the thickness results, followed by the choice of Young's modulus, which is poorly constrained for the Europan ice shell. Comparing our results to those of previously published flexure analyses for Europa, we infer spatial variability in the elastic ice thickness (at the time of load emplacement), with smooth bands having the thinnest elastic ice thickness of all areas studied. Because analysis of flexure-induced fracturing can only reveal the elastic thickness at the time of load emplacement, calculated thickness variability between features having different ages may also reflect a temporal variability in the thickness of Europa's ice shell.     

Limitations of Current Approaches for Predicting Groundwater Vulnerability from PFAS Contamination in the Vadose Zone

Published literature for reported sorption coefficients (K_d) of eight anionic per- and polyfluoroalkyl substances (PFAS) in soil was reviewed. K_d values spanned three to five log units indicating that no single value would be appropriate for use in estimating PFAS impacts to groundwater using existing soil-water partition equations. Regression analysis was used to determine if the soil or solution parameters might be used to predict K_d values. None of the 15 experimental parameters collected could individually explain variability in reported K_d values. Significant associations between K_d and soil calcium and sodium content were found for many of the selected PFAS, suggesting that soil cation content may be critical to PFAS sorption, as previously noted in sources like Higgins and Luthy (2006), while organic carbon content was significant only at elevated levels (>5%). Unexplained discrepancies between the results from studies where PFAS were introduced to soil and desorbed in the laboratory and those that used material from PFAS-impacted sites suggest that laboratory experiments may be overlooking some aspects critical to PFAS sorption. Future studies would benefit from the development and use of standardized analytical methods to improve data quality and the establishment of soil parameters appropriate for collection to produce more complete data sets for predictive analysis.     

Molecular asymmetry in extraterrestrial organic chemistry: An analytical perspective

The enantiomeric excesses determined for eight amino acids and one hydroxy acid of carbonaceous chondrite meteorites represent to date the only case of molecular asymmetry measured outside the biosphere. Because of the chiral homogeneity of life’s structures and functions, the findings have been debated for the possible relevance that a-biotic chiral symmetry-breaking might have had in the origin of terrestrial homochirality. While the many unknowns surrounding the origin of life have inevitably hindered the inquiries raised in this discourse, the hypotheses put forward in regard to the origin of extraterrestrial chiral asymmetry, which is a defined physico-chemical phenomenon, have been approached analytically and their scrutiny has aided the understanding of pre-biotic chemical evolution. We report here on our current knowledge of the asymmetric effects that could have influenced the chiral symmetry breaking of molecules in cosmochemical environments and how they correlate with the data obtained from meteorite analyses. We also address recent proposals that aqueous processes might have influenced the chirality of amino acids in meteorites and show that the crystallization behavior of isovaline, the most abundant non-racemic amino acid in the Murchison meteorite, excludes its attainment of enantiomeric excesses via phase changes such as crystallization or sublimation.     

Effects of human-induced alteration of groundwater flow on concentrations of naturally-occurring trace elements at water-supply wells

The effects of human-induced alteration of groundwater flow patterns on concentrations of naturally-occurring trace elements were examined in five hydrologically distinct aquifer systems in the USA. Although naturally occurring, these trace elements can exceed concentrations that are considered harmful to human health. The results show that pumping-induced hydraulic gradient changes and artificial connection of aquifers by well screens can mix chemically distinct groundwater. Chemical reactions between these mixed groundwaters and solid aquifer materials can result in the mobilization of trace elements such as U, As and Ra, with subsequent transport to water-supply wells. For example, in the High Plains aquifer near York, Nebraska, mixing of shallow, oxygenated, lower-pH water from an unconfined aquifer with deeper, confined, anoxic, higher-pH water is facilitated by wells screened across both aquifers. The resulting higher-O₂, lower-pH mixed groundwater facilitated the mobilization of U from solid aquifer materials, and dissolved U concentrations were observed to increase significantly in nearby supply wells. Similar instances of trace element mobilization due to human-induced mixing of groundwaters were documented in: (1) the Floridan aquifer system near Tampa, Florida (As and U), (2) Paleozoic sedimentary aquifers in eastern Wisconsin (As), (3) the basin-fill aquifer underlying the California Central Valley near Modesto (U), and (4) Coastal Plain aquifers of New Jersey (Ra). Adverse water-quality impacts attributed to human activities are commonly assumed to be related solely to the release of the various anthropogenic contaminants to the environment. The results show that human activities including various land uses, well drilling, and pumping rates and volumes can adversely impact the quality of water in supply wells, when associated with naturally-occurring trace elements in aquifer materials. This occurs by causing subtle but significant changes in geochemistry and associated trace element mobilization as well as enhancing advective transport processes.     

Artificial neural networks and geostatistical models for housing valuations in urban residential areas

Property valuation studies often use classical statistics techniques. Among these techniques, the Artificial Neural Networks are the most applied, overcoming the inflexibility and the linearity of the hedonic models. Other researchers have used Geostatistics techniques, specifically the Kriging Method, for interpreting spatial-temporal variability and to predict housing unit prices. The innovation of this study is to highlight how the Kriging Method can help to better understand the urban environment, improving the results obtained by classical statistics. This study presents two different methods that share the general objective of extracting information regarding a city’s housing from datasets. The procedures applied are Ordinary Kriging (Geostatistics) and Multi-Layer Perceptron algorithm (Artificial Neural Networks). These methods were used to predict housing unit prices in the municipality of Pozuelo de Alarcon (Madrid). The implementation of both methods provides us with the urban characteristics of the study area and the most significant variables related to price. The main conclusion is that the Ordinary Kriging models and the Neural Networks models, applied to predicting housing unit prices are necessary methodologies to improve the information obtained in classical statistical techniques.

Abbreviations: ANN: Artificial Neural Networks; OK: ordinary Kriging; MLP: multi-layer perceptron