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At least 73 records · Page 4Linked to original sources
PubMed1998

Geological evidence for solid-state convection in Europa's ice shell.

The ice-rich surface of the jovian satellite Europa is sparsely cratered, suggesting that this moon might be geologically active today. Moreover, models of the satellite's interior indicate that tidal interactions with Jupiter might produce enough heat to maintain a subsurface liquid water layer. But the mechanisms of interior heat loss and resurfacing are currently unclear, as is the question of whether Europa has (or had at one time) a liquid water ocean. Here we report on the morphology and geological interpretation of distinct surface features-pits, domes and spots-discovered in high-resolution images of Europa obtained by the Galileo spacecraft. The features are interpreted as the surface manifestation of diapirs, relatively warm localized ice masses that have risen buoyantly through the subsurface. We find that the formation of the features can be explained by thermally induced solid-state convection within an ice shell, possibly overlying a liquid water layer. Our results are consistent with the possibility that Europa has a liquid water ocean beneath a surface layer of ice, but further tests and observations are needed to demonstrate this conclusively.

Extraterrestrial Environment↗
PubMed1990

Voltammetric determination of platinum in inorganic complexes and in water, geological and biological matrices using laboratory- and field-based instrumentation.

The extremely sensitive catalytic hydrogen ion reduction wave observed after the formation of a platinum-formazone complex at a mercury electrode in a hydrazine-formaldehyde-H2SO4 medium has been utilised to determine platinum voltammetrically in well characterised platinum inorganic complexes (oxidation states O, II and IV) and in biological, geological and water samples. Experimental conditions have been optimised and sample-treatment procedures for various matrices have been critically evaluated for the quantification of platinum by the standard additions method. The determination of platinum in geological samples by this method has been compared with an inductively coupled plasma mass spectrometric method. Both conventional and portable field-based instrumentation have been used in the studies, and the possibility of developing a field-based method for the determination of platinum has been investigated. Despite the inherent sensitivity of the method, which enables concentrations down to 0.01 p.p.b. to be detected in simple matrices, natural levels in water and biological materials, where matrix effects suppress the voltammetric response, are often below the detection limit.

Animals↗
PubMed2005

Geologic constraints on the macroevolutionary history of marine animals.

The causes of mass extinctions and the nature of taxonomic radiations are central questions in paleobiology. Several episodes of taxonomic turnover in the fossil record, particularly the major mass extinctions, are generally thought to transcend known biases in the geologic record and are widely interpreted as distinct macroevolutionary phenomena that require unique forcing mechanisms. Here, by using a previously undescribed compilation of the durations of sedimentary rock sequences, I compare the rates of expansion and truncation of preserved marine sedimentary basins to rates of origination and extinction among Phanerozoic marine animal genera. Many features of the highly variable record of taxonomic first and last occurrences in the marine animal fossil record, including the major mass extinctions, the frequency distribution of genus longevities, and short- and long-term patterns of genus diversity, can be predicted on the basis of the temporal continuity and quantity of preserved sedimentary rock. Although these results suggest that geologically mediated sampling biases have distorted macroevolutionary patterns in the fossil record, preservation biases alone cannot easily explain the extent to which the sedimentary record duplicates paleobiological patterns. Instead, these results suggest that the processes responsible for producing variability in the sedimentary rock record, such as plate tectonics and sea-level change, may have been dominant and consistent macroevolutionary forces throughout the Phanerozoic.

Animals↗
PubMed1999

Biochemical evolution III: polymerization on organophilic silica-rich surfaces, crystal-chemical modeling, formation of first cells, and geological clues.

Catalysis at organophilic silica-rich surfaces of zeolites and feldspars might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and other geological sources. Crystal-chemical modeling yielded packings for amino acids neatly encapsulated in 10-ring channels of the molecular sieve silicalite-ZSM-5-(mutinaite). Calculation of binding and activation energies for catalytic assembly into polymers is progressing for a chemical composition with one catalytic Al-OH site per 25 neutral Si tetrahedral sites. Internal channel intersections and external terminations provide special stereochemical features suitable for complex organic species. Polymer migration along nano/micrometer channels of ancient weathered feldspars, plus exploitation of phosphorus and various transition metals in entrapped apatite and other microminerals, might have generated complexes of replicating catalytic biomolecules, leading to primitive cellular organisms. The first cell wall might have been an internal mineral surface, from which the cell developed a protective biological cap emerging into a nutrient-rich "soup." Ultimately, the biological cap might have expanded into a complete cell wall, allowing mobility and colonization of energy-rich challenging environments. Electron microscopy of honeycomb channels inside weathered feldspars of the Shap granite (northwest England) has revealed modern bacteria, perhaps indicative of Archean ones. All known early rocks were metamorphosed too highly during geologic time to permit simple survival of large-pore zeolites, honeycombed feldspar, and encapsulated species. Possible microscopic clues to the proposed mineral adsorbents/catalysts are discussed for planning of systematic study of black cherts from weakly metamorphosed Archaean sediments.

Animals↗
PubMed2003

Locating potential biosignatures on Europa from surface geology observations.

We evaluated the astrobiological potential of the major classes of geologic units on Europa with respect to possible biosignatures preservation on the basis of surface geology observations. These observations are independent of any formational model and therefore provide an objective, though preliminary, evaluation. The assessment criteria include high mobility of material, surface concentration of non-ice components, relative youth, textural roughness, and environmental stability. Our review determined that, as feature classes, low-albedo smooth plains, smooth bands, and chaos hold the highest potential, primarily because of their relative young age, the emplacement of low-viscosity material, and indications of material exchange with the subsurface. Some lineaments and impact craters may be promising sites for closer study despite the comparatively lower astrobiological potential of their classes. This assessment will be expanded by multidisciplinary examination of the potential for habitability of specific features.

Exobiology↗
PubMed2005

Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life.

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.

Evolution, Planetary↗
PubMed1989

Indoor Rn levels in different geological areas in Switzerland.

The distribution of indoor Rn concentrations in different geological areas in Switzerland was studied using passive alpha-track detectors. Measurements involving a sample of 400 single-family homes were made in the cellar, on the ground floor and the first floor, respectively. On the basis of a pilot survey, the country was divided into four zones in which the Rn distribution in houses was analyzed separately. The indoor exposure to Rn and Rn decay products is quite variable from region to region. The geology of the different areas was found to be an important factor in determining the mean value Rn levels. In the basin north of the Alps, where the population centers are located, a median Rn gas level of 47 Bq m-3 for the living area was found. The arithmetic mean value of 60 Bq m-3 in this region leads to an annual effective dose equivalent of about 1.8 mSv. For the population living in alpine areas, an arithmetic mean value exceeding 200 Bq m-3 will lead to an annual effective dose equivalent in the range of 6 mSv. The estimated exposure to Rn and Rn decay products for the upper one-percentile of the homes in the most affected alpine region even exceeds the annual limit of 50 mSv effective dose equivalent for occupational exposure.

Air Pollutants↗
PubMed1999

Validation of a geologically based radon risk map: are the indoor radon concentrations higher in high-risk areas?

Since geographically coded information is frequently used in studies of the relationships between environmental factors and illness at the population level and by authorities for promotion of mitigation, knowledge about the validity of proxy measures is essential. This study was an evaluation of a geologically based map describing the risk for high radon levels, which was used by the municipal authorities to determine the necessity of remedial actions. Annual mean radon gas concentrations for a random sample of one-family homes selected from high-risk areas (n = 252) were compared with those of a random sample of homes from normal and low-risk areas (n = 259). No difference in geometric mean radon concentration was found between the areas, 101 Bq m(-3) and 103 Bq m(-3), respectively. The proportion of homes in each area with radon gas concentrations above the current Swedish administrative limit value for mitigation (400 Bq m(-3)) was similar, approximately 10%. We conclude that the radon risk map was unsuitable for identifying areas of concern. The findings also indicate that geologically based and geographically coded information as a proxy for human exposures can be safely used for scientific and administrative purposes only following validation.

Air Pollution, Indoor↗
PubMed1991

Characterisation of palygorskite specimens from different geological locales for health hazard evaluation.

Palygorskite, a fibrous clay mineral, is being used as a substitute for asbestos in some applications. Nine specimens obtained from different geological locales were studied for mineral purity, elemental composition, fibre size distribution, and surface binding characteristics. The membranolytic activity of each was determined using a human erythrocyte model. The membranolytic behaviour and surface binding characteristics were compared with three chrysotile specimens employed as positive controls. The palygorskite specimens derived from the different geological locales display a range of physicochemical properties. This study shows the importance of selecting several mineral specimens for a health hazard evaluation. The current carcinogenic classification of the mineral may be limited due to the number of specimens used for that particular evaluation.

Asbestos↗
PubMedDate not supplied

Surface and subsurface geologic risk factors to ground water affecting brownfield redevelopment potential.

A model is created for assessing the redevelopment potential of brownfields. The model is derived from a space and time conceptual framework that identifies and measures the surface and subsurface risk factors present at brownfield sites. The model then combines these factors with a contamination extent multiplier at each site to create an index of redevelopment potential. Results from the application of the model within an urbanized watershed demonstrate clear differences between the redevelopment potential present within five different near-surface geologic units, with those units containing clay being less vulnerable to subsurface contamination. With and without the extent multiplier, the total risk present at the brownfield sites within all the geologic units is also strongly correlated to the actual costs of remediation. Thus, computing the total surface and subsurface risk within a watershed can help guide the remediation efforts at broad geographic scales, and prioritize the locations for redevelopment.

Cities↗
PubMed1989

Differences in cancer mortality rates in Ohio communities with respect to uraniferous geology.

Populations in areas of uraniferous geology may be at risk from radon emissions. Twenty-eight municipalities were examined as to their location with respect to uraniferous geology. Communities with possible radon risk had higher rates for all cancers and cancer of the respiratory system, but differences were not statistically significant. Some possible reasons for the results are discussed.

Geological Phenomena↗
PubMed1996

[Restricting effects of geologic background system on genuine crude drugs in Sichuan].

The distribution, growth, output and quality of genuine crude drugs are restricted by geologic background system (GBS), whose extensional vector system "rock-->soil-->medicinal plants" accomplishes the unity of geological grand cycle and biological pulmonary circulation. This article describes how genuine crude drugs in Sichuan, such as Coptis chinensis, etc. for example, are restricted by GBS.

Animals↗
PubMed2001

Acid digestion of geological and environmental samples using open-vessel focused microwave digestion.

The application of open vessel focused microwave acid digestion is described for the preparation of geological and environmental samples for analysis using inductively coupled plasma-mass spectrometry (ICP-MS). The method is compared to conventional closed-vessel high pressure methods which are limited in the use of HF to break down silicates. Open-vessel acid digestion more conveniently enables the use of HF to remove Si from geological and plant samples as volatile SiF4, as well as evaporation-to-dryness and sequential acid addition during the procedure. Rock reference materials (G-2 granite, MRG-1 gabbros, SY-2 syenite, JA-1 andesite, and JB-2 and SRM-688 basalts) and plant reference materials (BCR and IAEA lichens, peach leaves, apple leaves, Durham wheat flour, and pine needles) were digested with results comparable to conventional hotplate digestion. The microwave digestion method gave poor results for granitic samples containing refractory minerals, however fusion was the preferred method of preparation for these samples. Sample preparation time was reduced from several days, using conventional hotplate digestion method, to one hour per sample using our microwave method.

Acids, Noncarboxylic↗
PubMed2006

Quantifying the rainfall-water level fluctuation process in a geologically complex lake catchment.

Simulating hydrologic processes in geologically complex environments is a difficult scientific task since it incorporates high level of uncertainty. Many studies have attempted to accurately quantify the rainfall-water level elevation relationship in freshwater bodies so as to predict flooding and drought events. For this purpose several types of models have been implemented including distributed, black box and conceptual models that often provide efficient results, depending on the availability of reliable data as well as on the level of understanding of the system. Nevertheless, in the particular effort, three different models have been used to describe the relationship between rainfall and water level elevation in Trichonis Lake during the period 1951-1997. A Transfer Function model, a Dynamic Linear Regression and a physically based model, consisting of the lake's water budget equation, its Digital Bathymetric Model and GIS algorithms. These models have been tested to assess their efficiency and applicability in a karstic environment and the aim of the study was to find the best modeling option for developing sustainable water management plans and establishing a flooding/drought warning system in the particular lake catchment. The results indicated that in areas with geologically complex conditions, simple, physically-based models operate better than mechanistic models which usually cannot describe adequately the complexity of the system.

Algorithms↗
PubMed1992

On the negligible role of manned missions for the geological exploration of Mars: a commentary.

At the 28th Plenary Meeting of the Committee on Space Research (COSPAR) in The Hague, The Netherlands, there was on June 28, 1990, a session of commission MF.1 on Impact of Human Expeditions to Mars, in which, among others, the benefits of manned Mars missions for the geological survey of Mars were discussed. The present commentary does not intend to discuss the pros and cons of manned space flight or of Mars exploration at large, but will reiterate some of the points made in that discussion concerning the justification of manned versus automated Mars exploration in the context of geologic sciences.

Exobiology↗
PubMed2004

An investigation of the repeatability of calibration factors in gamma-ray spectrometry of geological materials.

A NaI(Tl)-based gamma spectrometer for the analysis of geological materials was calibrated using the IAEA reference materials RGU-1, RGTH-1 and RGK-1. To simulate typical geological samples, two additional standards were prepared from aliquots of the three reference materials. The reproducibility of the instrument calibration factors (CFs) was tested by repeated measurements of the pure IAEA reference materials and the mixed samples in a reproducible counting geometry. The results were analysed using a two-way classification analysis of variance; it was found that the variance in the CFs is significantly higher between standards than it is between measurements. Allowance should be made for this when estimating uncertainties in measurements with the NaI(Tl) spectrometers.

Calibration↗
PubMed2004

A simple method for 210Pb determination in geological samples by liquid scintillation counting.

A simple procedure for the determination of 210Pb in geological samples using liquid scintillation counting is presented. Following the acid digestion of the sample, the method uses sulphate precipitation for the radiochemical separation. Finally, lead oxalate is precipitated, and once re-dissolved, it is mixed with ULTIMA GOLD AB scintillator cocktail. The measurement is performed using a low-level LKB Quantulus 1220 spectrometer and the two-window technique. Calibration studies were performed to evaluate the interference of 210Bi in the 210Pb measurement. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.

Bismuth↗
PubMed1999

In situ imaging of microorganisms in geologic material.

In order to fully delineate the interactions of microorganisms with geological substrates, unequivocal identification of intact microbial cells within geologic samples is required without the disruption of either the rock texture or the relationship of the microorganisms to the mineral fabric. To achieve this objective we developed a protocol that enables the visualization of intact microbial cells in petrographic thin sections, avoids detaching the cells from their host mineral surfaces and avoids microbial contamination during the lapidary process. Propidium iodide and POPO-3, nucleic acid stains that specifically target double-stranded DNA and RNA were utilized for in situ visualization of cells in surface and subsurface basalts from northeastern Idaho. Additionally, examination of samples incubated with acetic acid-UL-14C via phosphor imagining facilitated the in situ visualization of 14C labeled biomass. Biomass observed was low (<10(7) cells/g). These observations indicate that the microbial distribution in these rocks exhibits a high degree of spatial heterogeneity at the sub-centimeter scale.

Bacteria↗