87,788 research outputs found
Les coûts dans l'entreprise ([Nouvelle éd.]) / F. et B. Grandguillot
No full textCollection : Les mémentos Foucher ; 7Contient une table des matièresAvec mode text
Kilmer (Martin F.), The shoulder bust in Sicily and South and Central Italy : a catalogue and materials for dating
No full textFoucher Louis. Kilmer (Martin F.), The shoulder bust in Sicily and South and Central Italy : a catalogue and materials for dating. In: Revue belge de philologie et d'histoire, tome 57, fasc. 2, 1979. Histoire (depuis l'Antiquité) - Geschiedenis (sedert de Oudheid) pp. 465-466
Traces of life on Mars are likely to be very small and very challenging to find
No full textThe volcanic materials at the surface of Mars provide an ideal potential habitat for chemolithotrophic microorganisms that obtain their energy from chemical reactions at the surfaces of minerals and their carbon from inorganic sources in the environment. If life ever appeared on Mars, hydrated environments in the Noachian period could have hosted such life forms. Other types of microorganisms that could possibly have lived at the surface during the Noachian include heterotrophic microorganisms that obtain their carbon source form organic carbon (either the degraded remains of pre-existing organisms or abiogenic sources). The rapid degradation in the environmental conditions at the surface of Mars imply an initially frozen and then dry surface that is unfavourable to the development of more sophisticated microorganisms, such as photosynthesisers. Whereas the latter produce readily recognisable macroscopic to microscopic structures, such as stromatolites and microbial mats, the former do not and their traces are very subtle and challenging to reveal. Fossilised chemolithotrophic microorganisms in littoral volcanic sands from the Early Archaean epoch (the Kitty’s Gap Chert in the Pilbara of Australia, c. 3.45 Ga) represent ideal analogues for eventual Noachian life in martian shallow water sediments. Surficial materials from this period, e.g. sediments and igneous rocks,
have been largely silicified because of high seawater silica saturation and extensive hydrothermal flushing of the environments and the Kitty’s Gap sediments as well as their microorganisms have been silicified. Investigations of the morphological and geochemical biosignatures of the early Archaean microfossils provide valuable information about the methods necessary to identify the fossils. The bulk carbon contents of the Kitty’s Gap Chert is < 0.01% and carbon isotope signatures range from – 25.9 to – 27.8 % . The microfossils are small, dividing coccoids 0.4-0.8 m in diameter that occur in colonial associations of many hundreds of individuals, the colonies reaching sizes of several tens of m in diameter. Because these sediments have been silicified, specific sample preparation involving delicate acid etching is necessary to reveal the microfossils. Although there may be other modes of preservation of microorganisms on Mars, the recent revelations of amorphous hydrothermal silica suggest that Noachian volcanic lithologies may have been silicified, as in the Early Archaean. Future in situ martian missions, such as MSL and ExoMars, carry microscopes but they will not be able to reveal the presence of individual microfossils like the chemolithotrophs of the Kitty’s Gap Chert and probably not even the colonies given the sample preparation necessary (the resolution of the MSL microscope is 12m and that of ExoMars is 4 m). However, Raman spectroscopy could identify carbonaceous phases and GC-MS could provide details of the organic composition, even at low bulk C concentrations. On the other hand, organic molecules in the Early Archaean cherts are very degraded and have generally lost their biogenic specificity. It may therefore not be possible to unambiguously identify martian biosignatures using in situ instrumentation and returning samples to Earth for detailed analysis in a terrestrial laboratory will probably be necessary
III. Religions de l'Inde
No full textLévi Sylvain, Foucher Alfred, Lacôte F. III. Religions de l'Inde. In: École pratique des hautes études, Section des sciences religieuses. Rapport sommaire sur les conférences de l'exercice 1904-1905 et le programme des conférences pour l'exercice 1905-1906. 1904. p. 46
Ferruginous biolaminations within the pre-Hirnantian (Late Ordovician) of the Carnic Alps, Austria
No full textWell preserved laminated structures occur within the Upper Ordovician of the Cellon section in the Carnic Alps (Austria), a world-famous reference section for Silurian conodont biostratigraphy. Microfacies from the Upper Ordovician Uqua Formation were characterised by using optical and scanning electron microscopy (SEM), an environmental scanning electron microscopy coupled with microanalyses (SEM/ESEM-EDX) and a confocal laser Raman microscopy. Ferruginous laminated structures overgrowing specific skeletal fragments occur in the lower part of the studied unit in the form of finely red-to greenish coatings composed of chamosite and goethite alternating with calcite bands. Laminae have arborescent to dendrolitic morphologies. Such morphologies suggest a biomediated genesis and the existence of a potential microbial factory acting in a nearby location from which coated material was later redeposited. These ferruginous coatings around organisms are not documented within the latest Ordovician Plöcken Formation at Cellon or in the coeval Wolayer Formation elsewhere.Well preserved laminated structures occur within the Upper Ordovician of the Cellon section in the Carnic Alps (Austria), a world-famous reference section for Silurian conodont biostratigraphy. Microfacies from the Upper Ordovician Uqua Formation were characterised by using optical and scanning electron microscopy (SEM), an environmental scanning electron microscopy coupled with microanalyses (SEM/ESEM-EDX) and a confocal laser Raman microscopy. Ferruginous laminated structures overgrowing specific skeletal fragments occur in the lower part of the studied unit in the form of finely red-to greenish coatings composed of chamosite and goethite alternating with calcite bands. Laminae have arborescent to dendrolitic morphologies. Such morphologies suggest a biomediated genesis and the existence of a potential microbial factory acting in a nearby location from which coated material was later redeposited. These ferruginous coatings around organisms are not documented within the latest Ordovician Plöcken Formation at Cellon or in the coeval Wolayer Formation elsewhere
ANCIENT BIOSIGNATURES IN ROCKS AND THEIR RELEVANCE IN THE SEARCH FOR EXTRATERRESTRIAL LIFE
No full textAstrobiological implications of microbes in basaltic pillow lava crusts: a case study from recent(bio-)alteration rims, Coral Patch Seamount, Atlantic Ocean
No full textAstrobiological implications of microbes in basaltic pillow lava crusts (Atlantic Ocean)
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