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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Accounts of chemical research 23 (1990), S. 84-87 
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 278 (1979), S. 479-479 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] TOWE REPLIES-Demoulin is disturbed primarily by my statement1 that unless the molecular oxygen requirement of chlorophyll-a had been a later modification, the evolution of this pig-ment in an anaerobic early Precambrian environment would have been unfavor-able. The ability of some extant blue-green ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 274 (1978), S. 239-240 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Thin rhombs of calcite were obtained by random cleavage of specimens of Iceland spar calcite. The rhombs were then prepared and mounted for ion-beam thinning parallel to the (1014) cleavage faces following the procedure of To we and Thompson1. The ion-thinned wafers were vacuum coated with ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 257 (1975), S. 115-116 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A corollary of the multiplicative creation model is that Einstein's cylindrical closed Universe suit cosmological considerations. Adopting the Einstein metric, and using the Einstein field equations, Dirac argues that if the radius of the Universe and G were constant and the galaxies were not ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 274 (1978), S. 657-661 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Recent biological–biochemical and geological–geochemical data are inconsistent with the currently accepted view that early Precambrian fossil microbiotas are evidence of oxygen-generating photosynthesis contributing free oxygen to early Precambrian environments. The alternative is ...
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 10 (1972), S. 38-48 
    ISSN: 1432-0827
    Keywords: Bivalve ; Molluse ; Shell ; Carbonates ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé La technique du bombardement à l'aide d'ion d'argon est utilisée pour réduire l'épaisseur de la coquille de carbonate de calcium des bivalvesMytilus etMercenaria pour examen au microscope électronique par transmission et en diffraction électronique; une comparaison est réalisée à l'aide de répliques simples, servant de témoins. Les résultats obtenus confirment les études antérieures de répliques et de microscopie par balayage. De plus, une structure “aérée” est mise en évidence dans la coquille des aragonites, et surtout dans le nacre deMytilus. Cette structure est interprêtée comme un artefact induit par la chaleur, formé par l'inclusion d'eau et de matériel organique, interprétation qui concorde avec les études chimiques et de microscopie électronique.
    Abstract: Zusammenfassung Die Beschießung mit Argonionen wurde angewendet, um die Dicke von Calciumcarbonat-Schalen der zweischaligen MuschelnMytilus undMercenaria zu reduzieren. Diese Technik erlaubte die Ausführung von Transmissions-Elektronenmikroskopie und Elektronendiffraktion, wobei gleiche Proben nach einer bereits bestehenden Methode vorbereitet und als Kontrollen herangezogen wurden. Es wurden zusätzliche Resultate zu den Muschelstruktur-studien erhalten, welche früher publizierte Arbeiten unterstützen, die mit der Abklatschmethode und der Raster-Elektronenmikroskopie ausgeführt worden waren. Zusätzlich wurde eine „schaumartige” Struktur der Muschelaragoniten, besonders im Perlmutter vonMytilus, beobachtet. Da es sich um ein durch Hitze verursachtes Artefakt handelt, wird diese Struktur als Einschlüsse von Wasser und organischem Material interpretiert, was den Befunden von verschiedenen veröffentlichten chemischen und elektronenmikroskopischen Arbeiten entspricht.
    Notes: Abstract Use is made of the argon ion-bombardment technique to reduce the thickness of calcium carbonate shells of the bivalvesMytilus andMercenaria for transmission electron microscopy and electron diffraction, with comparison of single-stage replicas of similar specimens serving as controls. As an additional approach to shell structure studies, it gives results which support earlier published work with both replicas and scanning microscopy. In addition, a “frothy” structure is detected in the shell aragonites, especially inMytilus nacre. As a heat-induced artifact, it is interpreted as representing trapped water and organic material inclusions, an interpretation consistent with several published chemical and electron microscope studies.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 15 (1985), S. 235-250 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract In the absence of direct evidence concerning the nature of the early Earth environments, it is acceptable under the uniformitarian principle to attempt to define primitive habitats from modern procaryotic physiology. Combining the rock and fossil record with present phylogenetic reconstuctions, application of this paleoecological approach to the evolutionary biochemistry and physiology of nitrogen fixation and photosynthesis leads to several inferences about the nature of Archean environments: 1. To stimulate nitrogenase evolution and avoid its repression, the activity of the NH 4 + ion was less than 10−3, and probably lower. 2. To be consistent with a moderately protective ozone screen, while not also repressing nitrogenase activity, incursions of abiotic dissolved oxygen at levels in the range 10−1.2−10−3.5 PAL would have been acceptable. 3. To induce the formation and activity of RuBP carboxylase, the pCO2 was less than 100 PAL. 4. To support Photosystem I activity, sulfide concentrations of at least 10−4 M were present in the photic zone. 5. To avoid a too-rapid oxidation of sulfide, the pH was probably between 6–7, where H2S exceeds HS−. Evolutionary ‘pressure’ to stimulate the later development of oxygenic photosynthesis (Photosystem II), would require several subsequent habitat modifications: 1. Lowering the sulfide to 〈 10−4 M to inhibit Photosystem I. 2. Raising the pH above neutral (HS− 〉 H2S), to mediate more rapid oxidation of HS−. 3. Maintaining either an illumination below 300–400 lux (to avoid photosynthetic O2 self-repression of nitrogen fixation), or an adequate local source of combined nitrogen (aNH 4 + 〉 10−4) to repress nitrogen fixation entirely.
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 348 (1990), S. 54-56 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In a classical Archaean environment the oxygen produced by net photosynthesis is not used by the aerobic heterotropic processes (aerobiosis) that today rapidly recycle it into carbon dioxide, nor is methane or ammonia oxidized biologically in the water column because methylotrophy and bacterial ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 295 (1982), S. 171-171 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SOME isotopic analyses of Precambrian reduced carbon which is strongly depleted in the heavier 13C isotope have been reported by Schoell and Wellmer1. They have argued that these anomalous graphitic carbons might be isotopically light as the result of a fractionation related to methane bacterial ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 288 (1980), S. 196-196 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] BURNS discussion1 on the possibility of the mineral feroxyhyte occurring on the surface of Mars is potentially misleading. In the original description of this mineral Chukhrov et al.2, following Feitknecht3, distinguished between a strongly magnetic phase, d-FeOOH, and a "practically nonmagnetic" ...
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