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Conference paperMuxworthy AR, Ridley V, Wang L, et al., 2008,
Comparing different methods of palaeointensity determination: a case study from the Datong volcanic province, China (poster)
, EGU -
Conference paperChang L, Roberts AP, Muxworthy AR, et al., 2008,
Fundamental magnetic properties of greigite (Fe3S4)
, EGU -
Conference paperMuxworthy AR, Williams W, 2008,
Critical superparamagnetic/single-domain grain-sizes in interacting magnetite particles: implications for magnetosomes
, EGU -
Journal articleChanton JP, Powelson DK, Abichou T, et al., 2008,
Application of nontraditional stable-isotope systems to the study of sources and fate of metals in the environment
, ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 42, Pages: 655-664, ISSN: 0013-936X- Author Web Link
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- Citations: 98
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Journal articleWombacher F, Rehkaemper M, Mezger K, et al., 2008,
Cadmium stable isotope cosmochemistry
, GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 72, Pages: 646-667, ISSN: 0016-7037- Author Web Link
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- Citations: 133
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Journal articleGulick SPS, Barton PJ, Christeson GL, et al., 2008,
Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater
, Nature Geoscience, Vol: 1 -
Conference paperBarron L, Williams W, Whaler K, et al., 2008,
The effect of nanoscale intergrowths on current palaeomagnetic interpretations (poster)
, Magnetic Moments -
Journal articleAubrey AD, Chalmers JH, Bada JL, et al., 2008,
The Urey Instrument: An Advanced In Situ Organic and Oxidant Detector for Mars Exploration
, Astrobiology, Vol: 8, Pages: 583-595, ISSN: 1531-1074The 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.
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Journal articleLomax BH, Fraser WT, Sephton MA, et al., 2008,
Plant spore walls as a record of long-term changes in ultraviolet-B radiation
, Nature Geoscience, Vol: 1, Pages: 592-596, ISSN: 1752-0894Stratospheric ozone screens the Earth's surface from harmful ultraviolet-B radiation. Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors, including solar cycles1, volcanic aerosols2, ozone-depleting substances3 and climate change4. However, assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy5. Here, we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss (Lycophyta) spores originating from high- and low-latitude localities, where they were exposed to different ultraviolet-B histories. We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern- and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation. Conversely, we find little change in the concentration of these compounds in spores originating from tropical Ecuador, where ultraviolet levels have remained relatively stable. Using spores from Greenland, we reconstruct past (1907–1993) changes in ozone concentration and ultraviolet-B flux; we reveal strong similarities between spore-wall reconstructions, and independent instrumental records6 and model results7. Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone. The chemical signature of plant spore walls in herbaria, and possibly also in sedimentary and ice-core archives, may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate.
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Journal articleCarvell RP, Sims MR, Sephton MA, et al., 2008,
The Search for Life on Mars
, Science in Parliament, Vol: 65, Pages: 12-13, ISSN: 0263-6271 -
Journal articleMartins Z, Botta O, Fogel ML, et al., 2008,
Extraterrestrial nucleobases in the Murchison meteorite
, EARTH PLAN SCI LETT, Vol: 270, Pages: 130-136, ISSN: 0012-821XCarbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ13C=+44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life's origin.
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Conference paperJiao D, Perry RS, Engel MH, et 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 articleSephton MA, Botta O, 2008,
Extraterrestrial organic matter and the detection of Life
, SPACE SCI REV, Vol: 135, Pages: 25-35, ISSN: 1572-9672A fundamental goal of a number of forthcoming space missions is the detection and characterization of organic matter on planetary surfaces. Successful interpretation of data generated by in situ experiments will require discrimination between abiogenic and biogenic organic compounds. Carbon-rich meteorites provide scientists with examples of authentic extraterrestrial organic matter generated in the absence of life. Outcomes of meteorite studies include clues to protocols that will enable the unequivocal identification of organic matter derived from life. In this chapter we summarize the diagnostic abiogenic features of key compound classes involved in life detection and discuss their implications for analytical instruments destined to fly on future spacecraft missions.
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Journal articleBada JL, Ehrenfreund P, Grunthaner F, et al., 2008,
Urey: Mars organic and oxidant detector
, SPACE SCI REV, Vol: 135, Pages: 269-279, ISSN: 1572-9672One of the fundamental challenges facing the scientific community as we enter this new century of Mars research is to understand, in a rigorous manner, the biotic potential both past and present of this outermost terrestrial-like planet in our solar system. Urey: Mars Organic and Oxidant Detector has been selected for the Pasteur payload of the European Space Agency’s (ESA’s) ExoMars rover mission and is considered a fundamental instrument to achieve the mission’s scientific objectives. The instrument is named Urey in recognition of Harold Clayton Urey’s seminal contributions to cosmochemistry, geochemistry, and the study of the origin of life. The overall goal of Urey is to search for organic compounds directly in the regolith of Mars and to assess their origin. Urey will perform a groundbreaking investigation of the Martian environment that will involve searching for organic compounds indicative of life and prebiotic chemistry at a sensitivity many orders of magnitude greater than Viking or other in situ organic detection systems. Urey will perform the first in situ search for key classes of organic molecules using state-of-the-art analytical methods that provide part-per-trillion sensitivity. It will ascertain whether any of these molecules are abiotic or biotic in origin and will evaluate the survival potential of organic compounds in the environment using state-of-the-art chemoresistor oxidant sensors.
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Journal articlePreston LJ, Benedix GK, Genge MJ, et 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: 0019-1035Surface 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.
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Journal articleMarlow JJ, Martins Z, Sephton MA, 2008,
Mars on Earth: soil analogues for future Mars missions
, ASTRON GEOPHYS, Vol: 49, Pages: 20-23, ISSN: 1366-8781Preparations for missions to Mars are a major concern for scientists. Predicting how equipment and experiments will perform on the planet is difficult because tests are restricted to Earth. Mars soil analogues are being used to solve this problem. These terrestrial materials are chemically and physically similar to martian soils and, because they contain unusual minerals and trace amounts of organic matter, are scientifically interesting in their own right. However,no current analogue is appropriate for all necessary tests. Here we describe Mars soil analogues, identify limitations and suggest the need for new Mars simulants.
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Book chapterGounell M, Morbidelli A, Bland PA, et al., 2008,
Meteorites from the Outer Solar System?
, The Solar System Beyond Neptune, Editors: Baruchi MA, Boenhardt H, Cruikshank DP, Morbidelli A, Barucci MA, Boehnhardt H, Cruikshank DP, Morbidelli A, Tucson, Arizona, Publisher: The University of Arizona Press, Pages: 525-541, ISBN: 978-0-8165-2755-7 -
Journal articleSephton MA, Carvell RP, Sims MR, et al., 2008,
The UK’s search for life on Mars
, ASTRON GEOPHYS, Vol: 49, Pages: 33-36, ISSN: 1366-8781 -
Journal articlePerry RS, Sephton MA, 2008,
Solving the mystery of desert varnish with microscopy
, In Focus, Vol: 11, Pages: 62-76, ISSN: 1750-4740In 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.
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Journal articleChang L, Roberts AP, Muxworthy AR, et al., 2007,
Magnetic characteristics of synthetic pseudo-single-domain and multi-domain greigite (Fe<sub>3</sub>S<sub>4</sub>)
, GEOPHYSICAL RESEARCH LETTERS, Vol: 34, ISSN: 0094-8276- Author Web Link
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- Citations: 31
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