346 research outputs found
Modeling pN2 through Geological Time: Implications for Planetary Climates and Atmospheric Biosignatures
Nitrogen is a major nutrient for all life on Earth and could plausibly play a
similar role in extraterrestrial biospheres. The major reservoir of nitrogen at
Earth's surface is atmospheric N2, but recent studies have proposed that the
size of this reservoir may have fluctuated significantly over the course of
Earth's history with particularly low levels in the Neoarchean - presumably as
a result of biological activity. We used a biogeochemical box model to test
which conditions are necessary to cause large swings in atmospheric N2
pressure. Parameters for our model are constrained by observations of modern
Earth and reconstructions of biomass burial and oxidative weathering in deep
time. A 1-D climate model was used to model potential effects on atmospheric
climate. In a second set of tests, we perturbed our box model to investigate
which parameters have the greatest impact on the evolution of atmospheric pN2
and consider possible implications for nitrogen cycling on other planets. Our
results suggest that (a) a high rate of biomass burial would have been needed
in the Archean to draw down atmospheric pN2 to less than half modern levels,
(b) the resulting effect on temperature could probably have been compensated by
increasing solar luminosity and a mild increase in pCO2, and (c) atmospheric
oxygenation could have initiated a stepwise pN2 rebound through oxidative
weathering. In general, life appears to be necessary for significant
atmospheric pN2 swings on Earth-like planets. Our results further support the
idea that an exoplanetary atmosphere rich in both N2 and O2 is a signature of
an oxygen-producing biosphere.Comment: 33 pages, 11 figures, 2 tables (includes appendix), published in
Astrobiolog
Putting Ethics on the Agenda for Real Estate Agents
This article uses sociological role theory to
help understand ethical challenges faced by Norwegian
real estate agents. The article begins with an introductory
case, and then briefly examines the strengths and limitations
of using legal definitions and rules for understanding
real estate agency and real estate agent ethics. It goes on to
argue that the ethical challenges of real estate agency can
be described and understood as a system of conflicting
roles with associated rights and duties, in particular sales
agent, intermediary and adviser sub-roles. The arguments
are developed using exploratory findings from a survey of
Norwegian real estate agents and from several focus
groups. The article then suggests the use of various
intranet tools as a kind of action research aimed at putting
ethics on the real estate agentsā agenda, working to
develop a collective conscience and collective selfcriticism
among the agents, and, in doing so, building
bridges between academic research and the practical
working world of the agents
Organisational structures and processes for health and well-being: insights from work integration social enterprise
Background: Previous research on employee well-being for those who have experienced social and economic disadvantage and those with previous or existing mental health conditions has focused mainly on programmatic interventions. The purpose of this research was to examine how organisational structures and processes (such as policies and culture) influence well-being of employees from these types of backgrounds. Methods: A case study ethnographic approach which included in-depth qualitative analysis of 93 semi-structured interviews of employees, staff, and managers, together with participant observation of four social enterprises employing young people. Results: The data revealed that young people were provided a combination of training, varied work tasks, psychosocial support, and encouragement to cultivate relationships among peers and management staff. This was enabled through the following elements: structure and space; funding, finance and industry orientation; organisational culture; policy and process; and fostering local service networks. The findings further illustrate how organisational structures at these workplaces promoted an inclusive workplace environment in which participants self-reported a decrease in anxiety and depression, increased self-esteem, increased self-confidence and increased physical activity. Conclusions: Replicating these types of organisational structures, processes, and culture requires consideration of complex systems perspectives on implementation fidelity which has implications for policy, practice and future research
Drake Equation for the Multiverse: From the String Landscape to Complex Life
It is argued that selection criteria usually referred to as "anthropic
conditions" for the existence of intelligent (typical) observers widely adopted
in cosmology amount only to preconditions for primitive life. The existence of
life does not imply in the existence of intelligent life. On the contrary, the
transition from single-celled to complex, multi-cellular organisms is far from
trivial, requiring stringent additional conditions on planetary platforms. An
attempt is made to disentangle the necessary steps leading from a selection of
universes out of a hypothetical multiverse to the existence of life and of
complex life. It is suggested that what is currently called the "anthropic
principle" should instead be named the "prebiotic principle."Comment: 6 pages, RevTeX, in press, Int. J. Mod. Phys.
Lattice-Boltzmann and finite-difference simulations for the permeability for three-dimensional porous media
Numerical micropermeametry is performed on three dimensional porous samples
having a linear size of approximately 3 mm and a resolution of 7.5 m. One
of the samples is a microtomographic image of Fontainebleau sandstone. Two of
the samples are stochastic reconstructions with the same porosity, specific
surface area, and two-point correlation function as the Fontainebleau sample.
The fourth sample is a physical model which mimics the processes of
sedimentation, compaction and diagenesis of Fontainebleau sandstone. The
permeabilities of these samples are determined by numerically solving at low
Reynolds numbers the appropriate Stokes equations in the pore spaces of the
samples. The physical diagenesis model appears to reproduce the permeability of
the real sandstone sample quite accurately, while the permeabilities of the
stochastic reconstructions deviate from the latter by at least an order of
magnitude. This finding confirms earlier qualitative predictions based on local
porosity theory. Two numerical algorithms were used in these simulations. One
is based on the lattice-Boltzmann method, and the other on conventional
finite-difference techniques. The accuracy of these two methods is discussed
and compared, also with experiment.Comment: to appear in: Phys.Rev.E (2002), 32 pages, Latex, 1 Figur
Environmental niches and metabolic diversity in Neoarchean lakes
Financial support for this study came from the NASA postdoctoral program (EES, REA), the NSF-FESD program (RB, TWL), the NASA Astrobiology Institute (TWL, NJP, and RB), and the NASA Exobiology program (grant NNX16AI37G to RB).The diversification of macro-organisms over the last 500 million years often coincided with the development of new environmental niches. Microbial diversification over the last 4 billion years likely followed similar patterns. However, linkages between environmental settings and microbial ecology have so far not been described from the ancient rock record. In this study, we investigated carbon, nitrogen, and molybdenum isotopes, and iron speciation in five non-marine stratigraphic units of the Neoarchean Fortescue Group, Western Australia, that are similar in age (2.78ā2.72Ā Ga) but differ in their hydro-geologic setting. Our data suggest that the felsic-dominated and hydrologically open lakes of the Bellary and Hardey formations were probably dominated by methanogenesis (Ī“13CorgĀ =Ā ā38.7Ā Ā±Ā 4.2ā°) and biologic N2 fixation (Ī“15NbulkĀ =ā0.6Ā Ā±Ā 1.0ā°), whereas the Mt. Roe, Tumbiana and Kylena Formations, with more mafic siliciclastic sediments, preserve evidence of methanotrophy (Ī“13Corg as low as ā57.4ā°, Ī“13Ccarb as low as ā9.2ā°) and NH3 loss under alkaline conditions. Evidence of oxygenic photosynthesis is recorded only in the closed evaporitic Tumbiana lakes marked by abundant stromatolites, limited evidence of Fe and S cycling, fractionated Mo isotopes (Ī“98/95MoĀ =Ā +0.4Ā Ā±Ā 0.4ā°), and the widest range in Ī“13Corg (ā57ā° to ā15ā°), suggesting oxidative processes and multiple carbon fixation pathways. Methanotrophy in the three mafic settings was probably coupled to a combination of oxidants, including O2 and SO42-. Overall, our results may indicate that early microbial evolution on the Precambrian Earth was in part influenced by geological parameters. We speculate that expanding habitats, such as those linked to continental growth, may have been an important factor in the evolution of life.PostprintPeer reviewe
An Archean Biosphere Initiative
The search for life on extrasolar planets will necessarily focus on the imprints of biolgy on the composition of planetary atmospheres. The most notable biological imprint on the modern terrestrial atmosphere is the presence of 21 % O2, However, during most of the past 4 billion years, life and the surface environments on Earth were profoundly different than they are today. It is therefore a major goal of the astrobiology community to ascertain how the O2 content of the atmosphere has varied with time. and to understand the causes of these variations. The NAI and NASA Exobiology program have played critical roles in developing our current understanding of the ancient Earth's atmosphere, supporting diverse observational, analytical, and computational research in geoscience, life science, and related fields. In the present incarnation of the NAI, ongoing work is investigating (i) variations in atmospheric O2 in the Archean to the Cambrian, (ii) characterization of the redox state of the oceans shortly before, during and after the Great Oxidation Event (GOE), and (iii) unraveling the complex connections between environmental oxygenation, global climate, and the evolution of life
Characterization of xenotime from Datas (Brazil) as a potential reference material for in situ U-Pb geochronology
CITATION: Vasconcelos, A. D. et al. 2018. Characterization of xenotime from Datas (Brazil) as a potential reference material for in situ U-Pb geochronology. Geochemistry, Geophysics, Geosystems, 19:2262ā2282, doi:10.1029/2017GC007412.The original publication is available at https://agupubs.onlinelibrary.wiley.comThis study investigates five megacrysts of xenotime (XN01, XN02, XN03, XN04, and XN05) as potential reference materials (RMs) for UāPb geochronology. These crystals belong to a 300 g xenotime assortment, collected from alluvial deposits in SE Brazil. Electron microprobe and Laser AblationāInductively Coupled PlasmaāMass Spectrometry (LAāICPāMS) analyses show that the selected crystals are internally homogeneous for most rare earth element, (REE, except some light REE) but are relatively heterogeneous for U and Th. The xenotime REE patterns are consistent with an origin from hydrothermal quartz veins in the Datas area that cut greenschistāfacies metasediments and that locally contain other accessory phases such as rutile and monazite. Highāprecision UāPb Isotope DilutionāThermal Ionization Mass Spectrometry (IDāTIMS) analyses showed slight age heterogeneity for the XN01 crystal not observed in the XN02 sample. The two crystals have slightly different average 206Pb/238U ages of 513.4 Ā± 0.5 Ma (2 s) and 515.4 Ā± 0.2 Ma (2 s), respectively. In situ UāPb isotope data acquired via LAā(Q,SF,MC)āICPāMS are within the uncertainty of the IDāTIMS data, showing homogeneity at the 1% precision of the laser ablation (and probably ion microprobe) technique. UāPb LAā(MC, SF)āICPāMS analyses, using XN01 as a primary RM, reproduced the ages of other established RMs within less than 1% deviation. Other Datas crystals (XN03ā05) also display a reproducibility in Pb/U dates better than 1% on LAāICPāMS, making them good candidates for further testing by IDāTIMS.https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2017GC007412Publisher's versio
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