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  • Journal article
    Court RW, Sephton MA, Parnell J, Gilmour Iet al., 2007,

    Raman spectroscopy of irradiated organic matter

    , GEOCHIM COSMOCHIM AC, Vol: 71, Pages: 2547-2568, ISSN: 0016-7037

    Raman spectroscopy of a range of irradiated and nonirradiated natural terrestrial bitumens has revealed that radiolytic alteration is generally associated with an increase in structural disorganisation. An interpretational methodology designed to overcome the considerable difficulties in obtaining reproducible, meaningful parameters of structural disorganisation is also presented, and should prove useful for future Raman applications. Raman investigation of a set of bitumens reported to have formed by the radiolytic polymerisation of light hydrocarbons, such as methane, has revealed excessive structural disorganisation, relative to biogenic complex-hydrocarbon-derived bitumens of similar radioelement concentrations, which may indicate the importance of precursor materials on the organic products of irradiation. Variations in the R1 ratio (D1/G band intensity) are found to be the best guide to variations in structural organisation. Comparisons of Raman spectra of the same sample, but produced by different exciting wavelengths, reveal the importance of the selection of a suitable laser wavelength. The results are discussed in terms of analyses of irradiated organic matter in the solar system, especially cometary nuclei and carbonaceous chondrites.
  • Journal article
    Parnell J, Cullen D, Sims MR, Bowden S, Cockell CS, Court R, Ehrenfreund P, Gaubert F, Grant W, Parro V, Rohmer M, Sephton M, Stan-Lotter H, Steele A, Toporski J, Vago Jet al., 2007,

    Searching for Life on Mars: Selection of Molecular Targets for ESA’s Aurora ExoMars Mission

    , Astrobiology, Vol: 7, Pages: 578-604, ISSN: 1531-1074

    The European Space Agency’s ExoMars mission will seek evidence of organic compounds of biological and non-biological origin at the martian surface. One of the instruments in the Pasteur payload may be a Life Marker Chip that utilizes an immunoassay approach to detect specific organic molecules or classes of molecules. Therefore, it is necessary to define and prioritize specific molecular targets for antibody development. Target compounds have been selected to represent meteoritic input, fossil organic matter, extant (living, recently dead) organic matter, and contamination. Once organic molecules are detected on Mars, further information is likely to derive from the detailed distribution of compounds rather than from single molecular identification. This will include concentration gradients beneath the surface and gradients from generic to specific compounds. The choice of biomarkers is informed by terrestrial biology but is wide ranging, and nonterrestrial biology may be evident from unexpected molecular distributions. One of the most important requirements is to sample where irradiation and oxidation are minimized, either by drilling or by using naturally excavated exposures. Analyzing regolith samples will allow for the search of both extant and fossil biomarkers, but sequential extraction would be required to optimize the analysis of each of these in turn.
  • Journal article
    Perry RS, Mcloughlin N, Lynne BY, Sephton MA, Oliver JD, Perry CC, Campbell K, Engel MH, Farmer JD, Brasier MD, Staley JTet al., 2007,

    Defining biominerals and organominerals: Direct and indirect indicators of life

    , SED GEOL, Vol: 201, Pages: 157-179, ISSN: 0037-0738
  • Journal article
    Pearson VK, Sephton MA, Gilmour I, 2006,

    Molecular and isotopic indicators of alteration in CR chondrites

    , METEORITICS & PLANETARY SCIENCE, Vol: 41, Pages: 1291-1303, ISSN: 1086-9379
  • Journal article
    Perry RS, Sephton MA, 2006,

    Desert varnish: an environmental recorder for Mars

    , ASTRONOMY & GEOPHYSICS, Vol: 47, Pages: 34-35, ISSN: 1366-8781
  • Journal article
    Sephton MA, James RH, Zolensky ME, 2006,

    The origin of dark inclusions in Allende: New evidence from lithium isotopes

    , METEORITICS & PLANETARY SCIENCE, Vol: 41, Pages: 1039-1043, ISSN: 1086-9379
  • Conference paper
    Sephton MA, Perry RS, Hoover RB, 2006,

    Thiophenes as indicators of aqueous alteration in carbonaceous meteorites

    , Conference on Instruments, Methods, and Missions for Astrobiology IX, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Journal article
    Ehrenfreund P, Sephton MA, 2006,

    Carbon molecules in space: from astrochemistry to astrobiology

    , FARADAY DISCUSSIONS, Vol: 133, Pages: 277-288, ISSN: 1359-6640
  • Conference paper
    Sephton MA, Self S, Verchovsky AB, Grady MM, Perry RS, Engel MH, Wright Iet al., 2006,

    Carbon isotopic gradients in the Martian crust: implications for past or present life on Mars

    , Conference on Instruments, Methods, and Missions for Astrobiology IX, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Conference paper
    Martins Z, Botta O, Fogel ML, Sephton MA, Glavin DP, Watson JS, Dworkin JP, Schwartz AW, Ehrenfreund Pet al., 2006,

    Isotopic analysis of nucleobases in the Murchison meteorite

    , METEORIT PLANET SCI
  • Book chapter
    Bland PA, Zolensky ME, Benedix GK, Sephton MAet al., 2006,

    Weathering of chondritic meteorites

    , Meteorites and the Early Solar System II, Editors: Lauretta, McSween, Lauretta, McSween, Arizona, Publisher: University of Arizona Press, Pages: 853-867, ISBN: 9780816525621
  • Book chapter
    Westall F, de Vries ST, Nijman W, Rouchon V, Oberger B, Pearson V, Watson J, Verchovsky A, Wright I, Rouzaud JN, Marchesini D, Anne Set al., 2006,

    The 3.466 Ga Kitty’s Gap Chert, an Early Archean microbial ecosystem

    , Processes on the early Earth, Editors: Reimold, Gibson, Publisher: Geological Society of Amer, ISBN: 9780813724058
  • Journal article
    Martins Z, Watson JS, Sephton MA, Botta O, Ehenfreund P, Gilmour Iet al., 2006,

    Free dicarboxylic and aromatic acids in the carbonaceous chondrites Murchison and Orgueil

    , Meteoritics & Planetary Science, Vol: 41, Pages: 1073-1080, ISSN: 1086-9379
  • Journal article
    Meredith W, Sun C-G, Snape CE, Sephton MA, Love GDet al., 2006,

    The use of model compounds to investigate the release of covalently bound biomarkers via hydropyrolysis

    , ORG GEOCHEM, Vol: 37, Pages: 1705-1714
  • Journal article
    Sephton MA, Howard LE, Bland PA, James RH, Russell SR, Prior DJ, Zolensky MEet al., 2006,

    Delving into Allende's dark secrets

    , ASTRON GEOPHYS, Vol: 47, Pages: 37-38, ISSN: 1366-8781
  • Journal article
    Pearson VK, Sephton MA, Franchi IA, Gibson JM, Gilmour Iet al., 2006,

    Carbon and nitrogen in carbonaceous chondrites:Elemental abundances and stable isotopic compositions

    , METEORIT PLANET SCI, Vol: 41, Pages: 1899-1918, ISSN: 1086-9379
  • Journal article
    Perry RS, Lynne BY, Sephton MA, Kolb VM, Perry CC, Staley JTet al., 2006,

    Baking black opal in the desert sun: the importance of silica in desert varnish, 2006, Geology, 34, 537-540

    , Geology, Vol: 34, Pages: 537-540, ISSN: 0091-7613
  • Journal article
    Court RW, Sephton MA, Parnell J, Gilmour Iet al., 2006,

    The alteration of organic matter in response to ionising irradiation: Chemical trends and implications for extraterrestrial sample analysis

    , Geochimica et Cosmochimica Acta, Vol: 70, Pages: 1020-1039

    Ionising radiation is an energy source capable of generating and altering complex organic matter. A full understanding of the radiolytic formation and devolution of organic matter is essential to appreciate the budget of organic chemicals that exist in cometary and interstellar ices, carbonaceous meteorites, and to understand the results of analyses of irradiated extraterrestrial organic matter, such as that in cometary nuclei. The effects of ionising radiation on a set of 10 naturally occurring, terrestrial organic assemblages have been revealed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), carbon isotopic analysis, and stepped combustion-isotope ratio mass spectrometry (SC-IRMS). Progressive radiolytic alteration of biogenic complex-hydrocarbon mixtures induces a decrease in the average size and extent of alkylation of polyaromatic hydrocarbons (PAH) and an increase in the abundance of oxygen-containing compounds, as indicated by Py-GC-MS, and an enrichment in C-13. These changes are attributed to reactions with free radicals, produced by ionising radiation. In contrast, the progressive radiolytic alteration of bitumens proposed to have derived from the radiolytic polymerisation of methane into an organic solid produces, upon pyrolysis, PAH of increasing average size and degree of alkylation. This, the opposite of the trend observed in the irradiated complex-hydrocarbons mixtures, cannot be explained in terms of the radiolytic alteration of a pre-existing array of complex organic molecules. Instead, it suggests the gradual construction of PAH from smaller molecules, supporting the hypothesis of a methane origin. Radiolytic alteration is also associated with a previously unrecognised increase in the mean combustion temperature of organic matter. This leads to predictions regarding the combustion characteristics of the irradiated organic matter present on cometary nuclei. A full understanding of the relationship between the combustion characteristics
  • Journal article
    Sephton MA, 2005,

    Organic matter in carbonaceous meteorites: past, present and future research

    , PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 363, Pages: 2729-2742, ISSN: 1364-503X
  • Journal article
    Sephton MA, Looy CV, Brinkhuis H, Wignall PB, de Leeuw JW, Visscher Het al., 2005,

    Catastrophic soil erosion during the end-Permian biotic crisis

    , GEOLOGY, Vol: 33, Pages: 941-944, ISSN: 0091-7613

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