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  • Journal article
    Perry RS, Sephton MA, 2008,

    Solving the mystery of desert varnish with microscopy

    , In Focus, Vol: 11, Pages: 62-76, ISSN: 1750-4740

    In areas such as Death Valley California whole mountains shimmer as light is reflected from widespread coatings of black opalescent desert varnish (Figure 1). Similar desert varnishes have been found on all continents, in locations such as the Gobi (Figure 2), Sonoran, Mojave, Namibian (Figure 3), Victorian and Atacama Deserts. These dark, lustrous coatings have attracted the interest of scientists for centuries. In 1852, the German naturalist and explorer Alexander Humboldt observed desert varnish on a transatlantic expedition and questioned how this enigmatic feature may have formed. His contemporary, Charles Darwin also engaged in the search for explanations for this unusual rock coating and, in 1871, attempted to satisfy his interest by performing chemical analyses. To date many other noteworthy scientists have examined desert varnish and have commented on its bulk chemistry, the arid conditions in which it forms in and the concentration of manganese that makes it opaque and causes it to be black.

  • Journal article
    Preston LJ, Benedix GK, Genge MJ, Sephton MAet al., 2008,

    A multidisciplinary study of silica sinter deposits with applications to silica identification and detection of fossil life on Mars

    , Icarus, Vol: 198, Pages: 331-350, ISSN: 0019-1035

    Surface features observed on Mars and evidence from martian meteorites both suggest that hydrothermal systems have operated in the crust of the planet. Hydrothermal systems are a potential habitat for living organisms and identifying these on Mars is, therefore, important in the search for life beyond the Earth. One of the surface expressions of hydrothermal systems on Earth are silica sinters, deposited during the cooling of hydrothermal solutions. In this paper we present analyses of the mineralogy, textures, chemistry and organic chemistry of silica sinters from two very different geothermal provinces, Waiotapu, New Zealand and Haukadalur, Iceland, in order to determine common features by which silica sinters can be identified. Infrared reflectance spectroscopy was utilised in combination with textural studies to evaluate the mineralogy of sinter deposits in terms of the abundances of different polymorphs of SiO2. Concentrations of organic molecules, principally lipids, within regions of the sinters in which there is textural evidence for micro-organisms were identified in the infrared spectral data and their presence was confirmed using gas chromatography mass spectroscopy. The results of this study indicate that reflectance spectra in the wavelength region from 2.5 to 14 μm, when calibrated against natural terrestrial analogues, can be used to identify silica sinters, as well as the possible presence of recent microbial communities on Mars.

  • Journal article
    Aubrey AD, Chalmers JH, Bada JL, Grunthaner FJ, Amashukeli X, Willis P, Skelley AM, Mathies RA, Quinn RC, Zent AP, Ehrenfreund P, Amundson R, Glavin DP, Botta O, Barron L, Blaney DL, Clark BC, Coleman M, Hofmann BA, Josset JL, Rettberg P, Ride S, Robert F, Sephton MA, Yen Aet al., 2008,

    The Urey Instrument: An Advanced In Situ Organic and Oxidant Detector for Mars Exploration

    , Astrobiology, Vol: 8, Pages: 583-595, ISSN: 1531-1074

    The Urey organic and oxidant detector consists of a suite of instruments designed to search for several classes of organic molecules in the martian regolith and ascertain whether these compounds were produced by biotic or abiotic processes using chirality measurements. These experiments will also determine the chemical stability of organic molecules within the host regolith based on the presence and chemical reactivity of surface and atmospheric oxidants. Urey has been selected for the Pasteur payload on the European Space Agency's (ESA's) upcoming 2013 ExoMars rover mission. The diverse and effective capabilities of Urey make it an integral part of the payload and will help to achieve a large portion of the mission's primary scientific objective: “to search for signs of past and present life on Mars.” This instrument is named in honor of Harold Urey for his seminal contributions to the fields of cosmochemistry and the origin of life.

  • Journal article
    Carvell RP, Sims MR, Sephton MA, Dannatt Let al., 2008,

    The Search for Life on Mars

    , Science in Parliament, Vol: 65, Pages: 12-13, ISSN: 0263-6271
  • Conference paper
    Jiao D, Perry RS, Engel MH, Sephton MAet al., 2008,

    Biomarker indicators of bacterial activity and organic fluxes during end Triassic mass extinction event (art. no. 709709)

    , Conference on Instruments, Methods, and Missions for Astrobiology XI, Publisher: The International Society for Optical Engineering, Pages: 1-12
  • Journal article
    Sephton MA, Meredith W, Sun C-G, Snape CEet al., 2007,

    Biomedical and forensic applications of combined catalytic hydrogenation-stable isotope ratio analysis

    , Analytical Chemistry Insights, Vol: 2, Pages: 37-42, ISSN: 1177-3901

    Studies of biological molecules such as fatty acids and the steroid hormones have the potential to benefit enormously from stable carbon isotope ratio measurements of individual molecules. In their natural form, however, the body’s molecules interact too readily with laboratory equipment designed to separate them for accurate measurements to be made.Some methods overcome this problem by adding carbon to the target molecule, but this can irreversibly overprint the carbon source ‘signal’. Hydropyrolysis is a newly-applied catalytic technique that delicately strips molecules of their functional groups but retains their carbon skeletons and stereochemistries intact, allowing precise determination of the carbon source. By solving analytical problems, the new technique is increasing the ability of scientists to pinpoint molecular indicators of disease, elucidate metabolic pathways and recognise administered substances in forensic investigations.

  • Journal article
    Watson JS, Sephton MA, Sephton SV, Self S, Fraser WT, Lomax BH, Gilmour I, Wellman CH, Beerling DJet al., 2007,

    Rapid determination of spore chemistry using thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy

    , PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, Vol: 6, Pages: 689-694, ISSN: 1474-905X
  • Journal article
    Siegert MJ, Behar A, Bentley M, Blake D, Bowden S, Christoffersen P, Cockell C, Corr H, Cullen DC, Edwards H, Ellery A, Ellis-Evans C, Griffiths G, Hindmarsh R, Hodgson DA, King E, Lamb H, Lane L, Makinson K, Mowlem M, Parnell J, Pearce DA, Priscu J, Rivera A, Sephton MA, Sims MR, Smith AM, Tranter M, Wadham JL, Wilson G, Woodward Jet al., 2007,

    Exploration of Ellsworth Subglacial Lake: a concept paper on the development, organisation and execution of an experiment to explore, measure and sample the environment of a West Antarctic subglacial lake

    , Reviews in Environmental Science and Biotechnology, Vol: 6, Pages: 161-179, ISSN: 1569-1705
  • Journal article
    Cockell CS, Kennerley N, Lindstrom M, Watson JS, Ragnarsdottir V, Sturkell E, Ott S, Tindle AGet al., 2007,

    Geomicrobiology of a weathering crust from an impact crater and a hypothesis for its formation

    , Geomicrobiology Journal: an international journal of geomicrobiology and microbial biogeochemistry, Vol: 24, Pages: 425-440

    Understanding the role of microbe-mineral interactions in rock weathering is vital to an understanding of nutrient availability to the biosphere and, in so far as weathering influences carbon dioxide drawdown, climate control. We studied a weathering crust on a resurge tsunami deposit (Loftarstone) from the 455 Ma old Lockne impact crater, central Sweden with an integrated approach using XRD, electron microprobe analysis, SEM-EDS and GCMS analysis of organics. The lichens and fungal hyphae network preferentially weather the chlorite in the Loftarstone compared to feldspars and quartz. We demonstrate, using a fungal isolate (identified by ITS sequencing), that biologically induced dissolution of the calcite component produces cavities which increase the surface area of interaction between the biota and the rock substrate. The weathering crust exfoliates from the rock surface in sheets, which we attribute to the dissolution of the calcite matrix. We present a hypothesis for the crust development. As well as providing insights into weathering on substrates derived from a diversity of high-energy geological disturbances, such as impact events and tsunamis, the weathering crust provides a model system to understand weathering processes in other common lithologies with mixed mineralogies at small spatial scales, including many sedimentary rocks. This work reveals how each different clast plays a unique part in the weathering process, leading to a well-defined weathering sequence.

  • Journal article
    Perry RS, Sephton MA, 2007,

    Baking black opal in the desert sun: The importance of silica in desert varnish: comment and reply

    , GEOLOGY, Vol: 35, Pages: e123-e123, ISSN: 0091-7613
  • Journal article
    Parbhakar A, Cuadros J, Sephton MA, Dubbin W, Coles BJ, Weiss Det al., 2007,

    Adsorption of L-lysine on montmorillonite

    , COLLOID SURFACE A, Vol: 307, Pages: 142-149, ISSN: 0927-7757

    Amino acid adsorption on smectite is relevant to prebiotic processes involving possible catalytic reactions in the early Solar System, as implied by the clay-organic correlation found in meteorites, and the generation and modification of organic components essential for the origin of life. Here we report the results of a study investigating the adsorption of l-lysine (0.025–0.4 M) onto montmorillonite. The reaction products were studied using X-ray diffraction, chemical analysis and infrared spectroscopy.We find that lysine adsorption is first dominated by cation exchange and then by adsorption of electrically neutral lysine (as a zwitterion), as indicated by chemical and FTIR evidence. At the maximum concentration, lysine displaces only ∼1/3 of the original interlayer cations. The d-spacing of the smectite–lysine complex increases from 1.2 to 2.1 nm as more lysine enters the interlayer space, and water is expelled. We propose a structural model of lysine sorption in the interlayer in which lysine is oriented at >45–90◦ to the plane of siloxane O atoms.

  • Journal article
    Wignall PB, Zonneveld J-P, Newton RJ, Amor K, Sephton MA, Hartley Set al., 2007,

    The end Triassic mass extinction record of Williston Lake, British Columbia

    , PALAEOGEOGR PALAEOCL, Vol: 253, Pages: 385-406, ISSN: 0031-0182
  • Journal article
    Pearson VK, Kearsley AT, Sephton MA, Gilmour Iet al., 2007,

    The labelling of meteoritic organic material using osmium tetroxide vapour impregnation

    , PLANET SPACE SCI, Vol: 55, Pages: 1310-1318, ISSN: 0032-0633
  • 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

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