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  • 1
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    The possible role of solid surface area in condensation reactions during chemical evolution - Reevaluation (1976)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Using surface concentration and reaction rate as the main criteria for the feasibility of condensation reactions, four types of prebiotic environments were analyzed: (1) an ocean-sediment system, (2) a dehydrated lagoon bed produced by evaporation, (3) the surface of a frozen sediment, and (4) a fluctuating system where hydration (rainstorms, tidal variations, flooding) and dehydration (evaporation) take place in a cyclic manner. With the possible exception of nucleotides, low adsorption of organomonomers on sediment surfaces of a prebiotic ocean (pH 8) is expected, and significant condensation is considered unlikely. In dehydrated and frozen systems, high surface concentrations are probable and condensation is more likely. In fluctuating environments, condensation rates will be enhanced and the size distribution of the oligomers formed during dehydration may be influenced by a 'redistribution mechanism' in which adsorbed oligomers and monomers are desorbed and redistributed on the solid surface during the next hydration-dehydration cycle.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 8; 4, 19; 1976
    Format: text
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  • 2
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    Origin of life (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The pathways of organic chemical synthesis, the chemical evolution on the early Earth leading to life was constrained by the development of the planet by accretion and core formation. The accretion and differentiation into the core-mantle-crust-atmosphere system strongly influenced the temperature and composition of the atmosphere, surface, and interior; but large gaps persist in our understanding of these processes. The time-span over which Earth acquired its volatiles, the composition of these volatiles, and the conditions under which outgassing of volatiles occurred to form the atmosphere, are unknown. Uncertainties in existing models for Earth accretion and early planetary development allows a wide range of possible prebiotic atmospheric compositions at the time and temperature when liquid water appeared and thermally-labile organic compounds could survive. These compositions range from strongly reducing atmospheres to mildly reducing ones.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: NASA, Washington The Global Sulfur Cycle; p 11-13
    Format: application/pdf
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  • 3
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    The Strecker synthesis from interstellar precursors as a source of amino acids in carbonaceous chondrites: Deuterium retention during synthesis (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-04-02
    Description: Amino acids in the Murchison carbonaceous chondrite are anomalously enriched in deuterium. Synthesis in Strecker reactions from D-enriched interstellar precursors during low temperature aqueous alteration of the parent body has been proposed by Cronin et al. (1988) to account for the isotopic observations. To test this hypothesis, we have measured the retention of deuterium in the glycine, alanine, and alpha-amino isobutyric acid produced, respectively, by reactions of formaldehyde-D2, acetaldehyde-D4, and acetone-D6 with HCN and NH3 in water.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Origins of Life and Evolution of the Biosphere (ISSN 0169-6149); 24; 2-4; p. 113-114
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  • 4
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    Amino acids and hydrocarbons approximately 3,800-Myr old in the Isua rocks, southwestern Greenland (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results of an analysis of amino acids and hydrocarbons found in the Isua banded iron formation, which contains the oldest known rocks on earth, are discussed. Similarities are pointed out between the relative amino acid abundances of the Isua rocks and those of lichens found on their surfaces, and a lack of substantial racemization indicated by the low D/L ratios in the 3800-million year old rock samples is noted. Experimental results showing the possibility of amino acid diffusion from lichens into the rocks are presented. Comparisons of the Isua rock amino acid D/L ratios with those reported for samples from other regions indicates that none of the Isua amino acids are older than a few tens of thousands to a few hundred thousand years. Analyses of the saturated hydrocarbons of the Isua samples reveals no odd carbon number preference, which may indicate antiquity, however laboratory experiments have shown that amino acids and aromatic and saturated aliphatic hydrocarbons could not have survived the metamorphic history of the Isua rocks. The evidence presented thus suggests that the amino acids and hydrocarbons found are not of the age of the sediments.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Nature; 289; Jan. 8
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  • 5
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    Cell wall and enzyme changes during the graviresponse of the leaf-sheath pulvinus of oat (Avena sativa) (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: The graviresponse of the leaf-sheath pulvinus of oat (Avena sativa) involves an asymmetric growth response and asymmetric processes involving degradation of starch and cell wall synthesis. Cellular and biochemical events were studied by investigation of the activities of related enzymes and changes in cell walls and their constituents. It is suggested that an osmotic potential gradient acts as the driving factor for growth, while wall extensibility is a limiting factor in pulvinus growth.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Plant Physiology (ISSN 0032-0889); p. 411-416.
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