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  • 1
    ISSN: 1432-1432
    Keywords: Primitive earth ; UV light ; Electric discharges ; Atmospheric phase ; Carbon chains ; Nitriles ; Aldehydes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The purpose of this paper is to compare the role of UV light and of electric discharges, the two most important sources of energy on the primitive earth, in the synthesis of organic compounds out of a reducing model of that atmosphere. Since Miller's experiments in 1953, most of the experimental simulations have been performed with electric discharges, and it has been assumed that UV radiations would give similar results. In order to check this assumption we have performed both experimental simulations in our laboratory. Experimental results indicate that this assumption was wrong in a large extent. Our four main conclusions are: 1. Unlike electric discharges, UV light is not an efficient source for producing unsaturated carbon chains. 2. UV light is efficient for producing nitriles in CH4-NH3 mixtures when the mole fraction of NH3 is very low while electric discharges need a higher mole fraction of NH3. 3. UV light is not able to produce nitriles from CH4-N2 mixtures while electric discharges produce important quantities of diversified nitriles from these mixtures. 4. UV light is not very efficient for producing aldehydes from CH4-H2O model atmosphere, electric discharges seem to be able to produce them more efficiently.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 80 (1998), S. 113-133 
    ISSN: 1573-0794
    Keywords: Planetary atmosphere ; laboratory simulation ; Titan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The main goals of experimental simulation in the laboratory of a planetary atmosphere are to feed the theoretical models, and to help the treatment of observations. This type of simulation permits the direct study of objects that space missions can't study or have not studied yet, through the production of laboratory analogues of gaseous or solid phases. But the representativity of these laboratory analogues is of crucial importance.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 8 (1977), S. 247-257 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract In order to evidence new reactions of prebiotic synthesis in aqueous solution between the S-containing compounds, such as alkanethiols, which can be obtained in gaseous phase during the simulation of the evolution of primitive atmosphere, and the malonic nitriles which are generally considered as important intermediates in the Chemical Evolution, a kinetic study on the eventual reactions of ethanethiol with cyanoacetaldehyde and malononitrile has been carried out. It appears that ethanethiol does not react directly in aqueous solution with cyanoacetaldehyde, but it gives an addition reaction with the double bond of the crotonic dimer of this malonic compound giving a thioether. With malononitrile, ethanethiol reacts directly by addition reaction on the CN group of the monomer, producing an iminothioester. These two reactions are equilibrated. The specific rate constants and the apparent equilibrium constants for these two reactions have been simultaneously studied by UV spectrophotometry at room temperature as a function of pH. The conditions for the formation of iminothioester will be discussed in terms of the respective pKa values of the thiol and of the malonic nitrile. These two addition products, principally the iminothioesters, because of their hydrolysis in thioesters may have played an important role in the prebiochemical evolution.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 28 (1998), S. 195-213 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of N2 and CH4, and including many organics. This atmosphere also partly consists of hazes and aerosol particles which shroud the surface of this satellite, giving it a reddish appearance. The aerosols observed in Titan's atmosphere are thought to be synthesized at high altitudes (〉300 km) and fall to the surface. Varying with temperature profiles, condensation phenomena take place in the lower atmosphere, about 100 km below. These solid particles, often called ‘tholins’, have been currently investigated for many years by laboratory scientists and physics modellers. This paper assesses past research and results in different fields (elemental composition, optical constants, pyrolysis, particle size), highlighting interests and questions aroused by these studies. It also presents the latest results and advances, and concludes with existing problems and future pathways.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 10 (1980), S. 371-377 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A conference on Life in the Universe, organized by the Council of Europe, and held in Paris, November 19 to 21, 1979, brought together more than 100 scientists from different fields. The aim of this conference was to promote scientific cooperation in Europe, in conjunction with other countries, in fields related to the problem of Life in the Universe. Our knowledge concerning this problem was reviewed in three different sessions. The first session was devoted to the question of planetary evolution; the second session was devoted to the question of the origin and evolution of life, and the third session was devoted to the problem of evolution of intelligence and the search for extraterrestrial intelligence. The Drake formula was the keynote of the conference. Each session tried to estimate some of the parameters of this formula, in order to examine the question: how many extraterrestrial civilizations with a level of technology at least equal to ours may be present in the universe? Even if no definite answer is given to this question, this meeting pointed out the need for more research.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 12 (1982), S. 267-279 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Numerous experiments have already been performed, simulating the evolution of gaseous mixtures containing CH4 when submitted to energy flux. From their results, it appears that a variety of organic compounds, including unsaturated hydrocarbons and nitriles such as HCN, can be synthesized into noticeable amounts from CH4−N2 mixtures. In particular, systematic studies of the influence of the composition of the mixture on the nature and amount of synthesized compounds show that organic volatile nitriles, and particularly cyanoacetylene and cyanogen, are formed only in media rich in nitrogen. Those nitriles have been identified very recently in the atmosphere of Titan, and thus, data from such laboratory experiments may provide important indirect information on the organic chemistry occuring at the periphery of this satellite of Saturn. However, during these experiments, there is a continuous formation and accumulation of molecular hydrogen, which does not occur in the atmosphere of Titan, because of H2 escape. In order to reassess the data already available from this type of laboratory studies, experiments on CH4−N2 atmospheres, with and without H2 escape, have been recently performed. The influence of this parameter on the chemical evolution of the atmosphere and on the nature and relative quantities of organic compounds has been studied. After reviewing these experiments, implications of the obtained results on the organic chemistry at the periphery of Titan are discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 14 (1984), S. 151-156 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Malonic nitriles are of great interest in prebiotic chemistry, because of the various organic reactions they can give in aqueous solutions. Among those, aminomalononitrile (AMN) plays a key role, as the trimer of HCN. In order to determine some of the thermodynamical data (pKA),...) and kinetic data relating to AMN in water, kinetic studies of the behaviour of AMN in aqueous solutions has been carried out at various pH. The preliminary results are reported concerning the determination of: Acid-base dissociation constants and U.V. and absorption coefficients
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 14 (1984), S. 157-162 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Previous kinetic studies on the addition of aliphatic thiols to activated nitriles suggest that the formation of iminothioesters (possible prebiotic precursors of thioesters) occurs through the nucleophilic addition of thiolate to the C=N group of the activated nitrile in its acidic form: $$R S^ {\ominus} + A - CH{_2} - C \equiv N {\overset {{H^ + }} \leftrightarrows} A - CH{_2} - \begin{array}{*{20}c} C \\ | \\ {SR} \\ \end{array} = NH$$ It seemed also that this addition occurs only when the pKA of the thiol is lower than the pKA of the activated nitrile. In order to test this hypothesis, and to generalize this mechanism, similar studies have been carried out using the same nitriles (A=CN; CHO), but with thiols having lower pKA (substituted thiophenols). The results of these studies, using p-aminothiophenol (pKA=6.85), p-chlorothiophenol (pKA=5.90) and p-nitrothiophenol (pKA=4.60), including the determination of rate and equilibrium constants, is presented.
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 2005-04-01
    Print ISSN: 1752-9298
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Elsevier
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  • 10
    Publication Date: 2013-01-06
    Description: [1]  The Upper Paleozoic geodynamic evolution is discussed at the scale of a wide part of Gondwana from North Africa to Arabia. With the aim of giving an integrated tectonic scenario for the study domain, we revisit six key areas, namely, the Anti-Atlas Belt (Morocco), the Bechar Basin (west Algeria), the Hassi R'Mel High (central Algeria), the Talemezane Arch (south Tunisia), the Western Desert (Egypt), and, finally, the High Zagros Belt (Iran). Below the so-called “Hercynian unconformity,” which is in reality a highly composite discontinuity, surface and subsurface data display a well-known arch-and-basin geometry, with basement highs and intervening Paleozoic basins. We show that this major feature results mainly from a Late Devonian event and can no longer be interpreted as a far effect of the Variscan Orogeny. This event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence, in the western part of the system, or by an important uplift of probable thermal origin followed by erosion and peneplanation. By the end of the Devonian, the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere. Such a primary configuration is preserved in Arabia with typical sag geometry of the Carboniferous and Permian deposits but strongly disturbed elsewhere by the conjugated effects of the Variscan Orogeny during the Carboniferous and/or by subsequent uplifts linked to the central Atlantic and Neo-Tethys rifting episodes. In conclusion, we try to integrate this new understanding in the geodynamics of the Late Devonian, which at world scale is characterized by the onset of the Variscan Orogeny on the one hand and by magmatism, rifting, and basement uplift on the other hand.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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