74 research outputs found
Depiction: Understanding Identity
http://deepblue.lib.umich.edu/bitstream/2027.42/69270/1/GalanteDoug_IPThesis2.pd
Effects of Gamma Ray Bursts in Earth Biosphere
We continue former work on the modeling of potential effects of Gamma Ray
Bursts on Phanerozoic Earth. We focus on global biospheric effects of ozone
depletion and show a first modeling of the spectral reduction of light by NO2
formed in the stratosphere. We also illustrate the current complexities
involved in the prediction of how terrestrial ecosystems would respond to this
kind of burst. We conclude that more biological field and laboratory data are
needed to reach even moderate accuracy in this modelingComment: Accepted for publication in Astrophysics & Space Scienc
Short-term Effects of Gamma Ray Bursts on Earth
The aim of the present work is to study the potential short-term atmospheric
and biospheric influence of Gamma Ray Bursts on the Earth. We focus in the
ultraviolet flash at the planet's surface, which occurs as a result of the
retransmission of the radiation through the atmosphere. This would be
the only important short-term effect on life. We mostly consider Archean and
Proterozoic eons, and for completeness we also comment on the Phanerozoic.
Therefore, in our study we consider atmospheres with oxygen levels ranging from
to 1% of the present atmospheric level, representing different
moments in the oxygen rise history. Ecological consequences and some strategies
to estimate their importance are outlined.Comment: 13 pp., to appear in Astrophysics and Space Scienc
Nanoscale 3D quantitative imaging of 1.88 Ga Gunflint microfossils reveals novel insights into taphonomic and biogenic characters
International audiencePrecambrian cellular remains frequently have simple morphologies, micrometric dimensions and are poorly preserved, imposing severe analytical and interpretational challenges, especially for irrefutable attestations of biogenicity. The 1.88 Ga Gunflint biota is a Precambrian microfossil assemblage with different types and qualities of preservation across its numerous geological localities and provides important insights into the Proterozoic biosphere and taphonomic processes. Here we use synchrotron-based ptychographic X-ray computed tomography to investigate well-preserved carbonaceous microfossils from the Schreiber Beach locality as well as poorly-preserved, iron-replaced fossil filaments from the Mink Mountain locality, Gunflint Formation. 3D nanoscale imaging with contrast based on electron density allowed us to assess the morphology and carbonaceous composition of different specimens and identify the minerals associated with their preservation based on retrieved mass densities. In the Mink Mountain filaments, the identification of mature kerogen and maghemite rather than the ubiquitously described hematite indicates an influence from biogenic organics on the local maturation of iron oxides through diagenesis. This non-destructive 3D approach to microfossil composition at the nanoscale within their geological context represents a powerful approach to assess the taphonomy and biogenicity of challenging or poorly preserved traces of early microbial life, and may be applied effectively to extraterrestrial samples returned from upcoming space missions
Comparative Survival Analysis of Deinococcus Radiodurans and the Haloarchaea Natrialba Magadii and Haloferax Volcanii, Exposed to Vacuum Ultraviolet Irradiation
The haloarchaea Natrialba magadii and Haloferax volcanii, as well as the
radiation-resistant bacterium Deinococcus radiodurans, were exposed to
vacuum-UV (V-UV) radiation at the Brazilian Synchrotron Light Laboratory
(LNLS). Cell monolayers (containing 105 - 106 cells per sample) were prepared
over polycarbonate filters and irradiated under high vacuum (10-5 Pa) with
polychromatic synchrotron radiation. N. magadii was remarkably resistant to
high vacuum with a survival fraction of ((3.77 \pm 0.76) x 10-2), larger than
the one of D. radiodurans ((1.13 \pm 0.23) x 10-2). The survival fraction of
the haloarchaea H. volcanii, of ((3.60 \pm 1.80) x 10-4), was much smaller.
Radiation resistance profiles were similar between the haloarchaea and D.
radiodurans for fluencies up to 150 J m-2. For fluencies larger than 150 J m-2
there was a significant decrease in the survival of haloarchaea, and in
particular H. volcanii did not survive. Survival for D. radiodurans was 1%
after exposure to the higher V-UV fluency (1350 J m-2) while N. magadii had a
survival lower than 0.1%. Such survival fractions are discussed regarding the
possibility of interplanetary transfer of viable micro-organisms and the
possible existence of microbial life in extraterrestrial salty environments
such as the planet Mars and the Jupiter's moon Europa. This is the first work
reporting survival of haloarchaea under simulated interplanetary conditions.Comment: Draft version (without figures), Accepted for publication in
Astrobiolog
Ecological interactions in Cloudina from the Ediacaran of Brazil : implications for the rise of animal biomineralization.
At the Ediacaran/Cambrian boundary, ecosystems witnessed an unparalleled biological innovation:
the appearance of shelled animals. Here, we report new paleoecological and paleobiological data on
Cloudina, which was one of the most abundant shelled animals at the end of the Ediacaran. We report
the close association of Cloudina tubes with microbial mat textures as well as organic-rich material,
syndepositional calcite and goethite cement between their flanges, thus reinforcing the awareness of
metazoan/microorganism interactions at the end of the Ediacaran. The preservation of in situ tubes
suggests a great plasticity of substrate utilization, with evidence of different life modes and avoidance
behavior. Geochemical analysis revealed walls composed of two secondary laminae and organic sheets.
Some walls presented boreholes that are here described as predation marks. Taken together, these data
add further information regarding the structuring of shelled animal communities in marine ecosystems
Evidence for Metabolic Diversity in Meso-Neoproterozoic Stromatolites (Vazante Group, Brazil)
Deciphering the evolution of ecological interactions among the metabolic types during the early diversification of life on Earth is crucial for our understanding of the ancient biosphere. The stromatolites from the genus Conophyton cylindricus represent a datum for the Proterozoic (Meso to Neoproterozoic) on Earth. Their typical conical shape has been considered a result of a competition between microorganisms for space, light and nutrients. Well-preserved records of this genus from the Paleontological Site of Cabeludo , Vazante Group, São Francisco Craton (Southern Brazil) present in situ fossilized biofilms, containing preserved carbonaceous matter. Petrographic and geochemical analyses revealed an alternation between mineral laminae (light grey laminae) and fossilized biofilms (dark grey laminae). The dark grey laminae comprise three different biofilms recording a stratified microstructure of microbial communities. These three biofilms composing the dark grey laminae tend to be organized in a specific pattern that repeats through the stromatolite vertical section. Iron and manganese are distributed differently along the dark and light grey laminae; X-ray absorption and luminescence data showed possible different areas with authigenic iron and iron provided from diagenetic infiltration. Cryptocrystalline apatite in the lowermost biofilms in each dark grey laminae may suggest past metabolic activity of sulfide-oxidizing bacteria. These findings suggest that the microorganisms reached a complex metabolic diversification in order to maintain an equilibrium situation between the three different biofilms along the vertical section of the structures, thus benefiting the whole microbial community. This means that the stromatolites from the Conophyton genus may have formed as a result of a greater complexity of interactions between microorganisms, and not only from competition between photosynthesizers
Adenine interaction with and adsorption on Fe-ZSM-5 zeolites: A prebiotic chemistry study using different techniques
Most adsorption experiments are performed under conditions that did not exist on Earth before the life arose on it. Because adsorption is the first step for all other processes (protection against degradation and polymerization), it is important that it is performed under conditions that existed on prebiotic Earth. In this paper, we use an artificial seawater (seawater 4.0 Ga), which contains major cations and anions that could present on the oceans of the prebiotic Earth. In addition, zeolites, with substituted Fe in the framework, and adenine were probably common substances on the prebiotic Earth. Thus, study the interaction between them is an important issue in prebiotic chemistry. There are two main findings described in this paper. Firstly, zeolites with different Si/Fe ratios adsorbed adenine differently. Secondly, XAFS showed that, after treatments with seawater 4.0 Ga and adenine, an increase in the complexity of the system occurred. In general, salts of seawater 4.0 Ga did not affect the adsorption of adenine onto zeolites and adenine adsorbed less onto zeolites with iron isomorphically substituted. The C=C and NH2 groups of adenine interacted with the zeolites. Gypsum, formed from aqueous species dissolved in seawater 4.0 Ga, precipitated onto zeolites. EPR spectra of zeolites showed lines caused by Fe framework and Fe3+ species. TG curves of zeolites showed events caused by loss of water weakly bound to zeolite (in the 30-140 °C range), water bounded to iron species or cations from seawater 4.0 Ga or located in the cavities of zeolites (157-268 °C) and degradation of adenine adsorbed onto zeolites (360-600 °C). Mass loss follows almost the same order as the amount of adenine adsorbed onto zeolites. The XAFS spectrum showed that Fe3+ could be substituted into the framework of the Fe7-ZSM-5 zeolite
Insights into the Skeletonization, Lifestyle, and Affinity of the Unusual Ediacaran Fossil Corumbella
The Ediacaran fossil Corumbella is important because it is hypothesized to be a scyphozoan\ud
cnidarian, and thus might be one of the rare examples of bona fide Neoproterozoic nimals.\ud
Unfortunately, its mode of life, style of skeletonization, and taxonomic affinity have been very controversial. Here, we use X-ray micro-CT, SEM, and taphonomic analysis to compare preservational modes of Corumbella, in order to better understand the symmetry, mode of construction, preservational style, and taxonomy of this group. Results suggest that articulated and disarticulated specimens of Corumbella from the Ediacaran of Brazil, Paraguay, and the United States, although sometimes preserved very differently, represent\ud
the same taxon—Corumbella werneri. Corumbellids had a thick but flexible theca and probably lived with their basalmost part anchored in the sediment, much like Conotubus. When considered together, these results suggest that Corumbella was one of the first animals to build a skeleton, employing a lamellar microfabric similar to conulariids.FAPESP (Proc. 2009/02312-4)NAPAstrobio (PRP-USP)FAPESP (Proc. 2011/50242-5)CNPq (562143/ 2010-6, 458555/2013-4)CAPES.Astrobiology Laboratory (AstroLab, IAG-USP)LNNano/CNPEMNP-BioMa
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