Publications
Results
- Showing results for:
- Reset all filters
Search results
-
Journal articleKamo S, Lana C, Morgan J, 2011,
U–Pb ages of shocked zircon grains link distal K–Pg boundary sites in Spain and Italy with the Chicxulub impact
, Earth and Planetary Science Letters, Vol: 310, Pages: 401-408The U–Pb ages of shocked zircon crystals from the Chicxulub impact crater and Cretaceous-Paleogene (K-Pg) boundary sites in Haiti, the USA, and Canada, and the pattern of decreasing particle size with paleodistance from the crater, have been used as evidence of a genetic link between Chicxulub and the K–Pg boundary. Despite this, the inference that the K–Pg boundary layer formed as a direct consequence of the Chicxulub impact has been repeatedly questioned. Here we present U–Pb (ID-TIMS) ages and textural evidence of shock metamorphosed zircon grains from the K–Pg boundary at Caravaca, Spain, and Petriccio, Italy, that establish a causal connection between the impact and formation of the K–Pg boundary layer. The shocked zircon grains give data that produce a characteristic age pattern, which indicates a primary source age of 549.5 ± 5.7 Ma and a secondary event at the approximate time of impact at 66 Ma. The intensity of the shock features is proportional to the degree of isotopic resetting, and all textural features and ages are analytically identical to those of previously analyzed zircon from Chicxulub and K–Pg boundary sites in North America. Caravaca and Petriccio were > 8000 km from Chicxulub at the time of impact, and are therefore the farthest K–Pg sites identified that can be linked to Chicxulub through the dating of individual shocked zircon grains. We conclude that the combined age data and textural observations provide unambiguous evidence that ejecta from the Chicxulub impact formed the global K–Pg boundary layer. These data cannot be explained by the alternative scenario that the Chicxulub impact occurred ~ 300 ka prior to the K–Pg boundary.
-
Conference paperMuxworthy AR, 2011,
Magnetic interactions: Love thy neighbour?
, BGA Advanced in Geophysics -
Journal articleWilliams W, Muxworthy AR, Evans ME, 2011,
A micromagnetic investigation of magnetite grains in the form of Platonic polyhedra with surface roughness
, Geochemistry, Geophysics, Geosystems, Vol: 12 -
Journal articleLarner F, Rehkaemper M, Coles BJ, et al., 2011,
A new separation procedure for Cu prior to stable isotope analysis by MC-ICP-MS
, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 26, Pages: 1627-1632, ISSN: 0267-9477- Author Web Link
- Cite
- Citations: 49
-
Journal articleFraser WT, Sephton MA, Watson JS, et al., 2011,
UV-B absorbing pigments in spores: biochemical responses to shade in a high-latitude birch forest and implications for sporopollenin-based proxies of past environmental change
, Polar Research, Vol: 30, Pages: 8312-8318, ISSN: 1751-8369Current attempts to develop a proxy for Earth’s surface ultraviolet-B (UV-B) flux focus on the organic chemistry of pollen and spores because their constituent biopolymer, sporopollenin, contains UV-B absorbing pigments whose relative abundance may respond to the ambient UV-B flux. Fourier transform infrared (FTIR microspectroscopy provides a useful tool for rapidly determining the pigment content of spores. In this paper, we use FTIR to detect a chemical response of spore wall UV-B absorbing pigments that correspond with levels of shade beneath the canopy of a high-latitude Swedish birch forest. A 27% reduction in UV-B flux beneath the canopy leads to a significant (p<0.05) 7.3% reduction in concentration of UV-B absorbing compounds in sporopollenin. The field data from this natural flux gradient in UV-B further support our earlier work on sporopollenin-based proxies derived from sedimentary records and herbaria collections.
-
Journal articleVisscher H, Sephton MA, Looy CV, 2011,
Fungal virulence at the time of the end-Permian biosphere crisis?
, GEOLOGY, Vol: 39, Pages: 883-886, ISSN: 0091-7613Throughout the world, latest Permian records of organic-walled microfossils are characterized by the common presence of remains of fi lamentous organisms, usually referred to the palynomorph genus Reduviasporonites. Although generally regarded as indicators of global ecological crisis, fundamental controversy still exists over the biological and ecological identity of the remains. Both fungal and algal affinities have been proposed. We seek to resolve this enigma by demonstrating close morphological similarity of the microfossils to resting structures (monilioid hyphae, sclerotia) of Rhizoctonia, a modern complex of soil-borne filamentous fungi that includes ubiquitous plant pathogens. By analogy with present-day forest decline, these findings suggest that fungal virulence may have been a significant contributing factor to widespread devastation of arboreal vegetation at the close of the Permian Period.
-
Journal articleGowen RA, Smith A, Fortes AD, et al., 2011,
Penetrators for in situ subsurface investigations of Europa
, ADV SPACE RES, Vol: 48, Pages: 725-742, ISSN: 0273-1177We present the scientific case for inclusion of penetrators into the Europan surface, and the candidate instruments which could significantly enhance the scientific return of the joint ESA/NASA Europa-Jupiter System Mission (EJSM). Moreover, a surface element would provide an exciting and inspirational mission highlight which would encourage public and political support for the mission.Whilst many of the EJSM science goals can be achieved from the proposed orbital platform, only surface elements can provide key exploration capabilities including direct chemical sampling and associated astrobiological material detection, and sensitive habitability determination. A targeted landing site of upwelled material could provide access to potential biological material originating from deep beneath the ice.Penetrators can also enable more capable geophysical investigations of Europa (and Ganymede) interior body structures, mineralogy, mechanical, magnetic, electrical and thermal properties. They would provide ground truth, not just for the orbital observations of Europa, but could also improve confidence of interpretation of observations of the other Jovian moons. Additionally, penetrators on both Europa and Ganymede, would allow valuable comparison of these worlds, and gather significant information relevant to future landed missions. The advocated low mass penetrators also offer a comparatively low cost method of achieving these important science goals.A payload of two penetrators is proposed to provide redundancy, and improve scientific return, including enhanced networked seismometer performance and diversity of sampled regions.We also describe the associated candidate instruments, penetrator system architecture, and technical challenges for such penetrators, and include their current status and future development plans.
-
Journal articleMorgan JV, Warner MR, Collins GS, et al., 2011,
Full waveform tomographic images of the peak ring at the Chicxulub impact crater
, Journal of Geophysical Research, Vol: 116Peak rings are a feature of large impact craters on the terrestrial planets and are generally believed to be formed from deeply buried rocks that are uplifted during crater formation. The precise lithology and kinematics of peak ring formation, however, remains unclear. Previous work has revealed a suite of bright inward-dipping reflectors beneath the peak ring at the Chicxulub impact crater and that the peak ring was formed from rocks with a relatively low seismic velocity. New 2D full-waveform tomographic velocity images show that the uppermost lithology of the peak ring is formed from a thin (~100-200 m thick) layer of low-velocity (~3000-3200 m/s) rocks. This low-velocity layer is most likely to be composed of highly porous, allogenic impact breccias. Our models also show that the change in velocity between lithologies within and outside the peak ring is more abrupt than previously realized and occurs close to the location of the dipping reflectors. Across the peak ring, velocity appears to correlate well with predicted shock pressures from a dynamic model of crater formation, where the rocks that form the peak ring originate from uplifted basement that has been subjected to high shock pressures (10-50 GPa), and lie above downthrown sedimentary rocks that have been subjected to shock pressures of < 5 GPa. These observations suggest that low-velocities within the peak ring may be related to shock effects and that the dipping reflectors underneath the peak ring might represent the boundary between highly-shocked basement and weakly-shocked sediments.
-
Journal articleMuxworthy AR, Ji X, Ridley V, et al., 2011,
Multi-protocol palaeointensity determination from middle Brunhes Chron volcanics, Datong Volcanic Province, China
, Physics of the Earth and Planetary Interiors, Vol: 187, Pages: 188-198 -
Journal articleEhrenfreund P, Roling WFM, Thiel CS, et al., 2011,
Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota
, International Journal of Astrobiology, Vol: 10, Pages: 239-253 -
Journal articleSephton MA, Court RW, Baki AO, et al., 2011,
New Solvents for Space Missions: Utility for Life Detection Instruments and Notable Terrestrial Applications
, Recent Patents on Space Technology, Vol: 1, Pages: 7-11, ISSN: 2210-6871Instruments designed to test for signs of life on Mars must have operational simplicity and efficiency. One example is the Life Marker Chip being developed to fly on the forthcoming European Space Agency ExoMars mission. Target organic compounds include both polar and non polar molecules and, prior to our patented discovery, no solvent had been tested which effectively extracted both types of molecule in a fashion which was compatible with antibodybased detectors. We have compared the extraction efficiency of water-based solvents alongside conventional organic solvents to determine their suitability for extracting organic mixtures on space missions. Using a range of hydrocarbon standards and a Mars regolith simulant (JSC Mars-1) we have concluded that a water-methanol mix with 1.5 to 2.5 g/L of polysorbate 80 represents the most suitable solvent with extraction efficiencies that can achieve up to approximately 30% of that using conventional organic solvents (assuming 100%efficiency with 93:7 (vol:vol) dichloromethane:methanol mixtures). The surfactant solution will also provide solutions to terrestrial problems, one of which is explored in the patented work.
-
Journal articleCourt RW, Sephton MA, 2011,
The contribution of sulphur dioxide from ablating micrometeorites to the atmospheres of Earth and Mars
, GEOCHIM COSMOCHIM AC, Vol: 75, Pages: 1704-1717, ISSN: 0016-7037Atmospheric composition is a key control on climate and the habitability of planetary surfaces. Ablation of infalling micrometeorites has been recognised as one way in which atmospheric chemistry can be changed, especially at times in solar system history when the infall rates of exogenous material were high. Despite its potential to influence climate and habitability, extraterrestrial sulphur dioxide is currently an unquantified contribution to the atmospheres of the terrestrial planets. We have used flash pyrolysis to simulate the atmospheric entry of micrometeorites and Fourier-transform infrared spectroscopy to identify and quantify the sulphur dioxide produced from the carbonaceous meteorites Orgueil (CI1), ALH 88045 (CM1), Cold Bokkeveld (CM2), Murchison (CM2) and Mokoia (CV3). We have used this approach to understand the introduction of sulphur dioxide to the atmospheres of Earth and Mars from infalling micrometeorites. Sulphates, present in carbonaceous chondrites at a few wt.%, are resistant to thermal decomposition, limiting the yields of sulphur dioxide from unmelted micrometeorites. Infalling micrometeorites are a minor source of present-day sulphur dioxide on Earth and Mars, calculated to be up to around 2400 tonnes and about 350 tonnes, respectively. During the Late Heavy Bombardment (LHB), the much greater infall rates of micrometeoritic dust are calculated to be associated with average production rates of sulphur dioxide of around 20 Mt yr 1 for the early Earth and 0.5 Mt yr 1 for early Mars, for a LHB of 100 Myr. These rates of delivery of sulphur dioxide at high altitudes would have reduced the solar energy reaching the surfaces of these planets, via scattering of sunlight by stratospheric sulphate aerosols, and may have had detrimental effects on developing biospheres by promoting cooler climates and reducing the probability of liquid water on planetary surfaces.
-
Journal articleMartins Z, Sephton MA, Foing BH, et al., 2011,
Extraction of amino acids from soils close to the Mars Desert Research Station (MDRS), Utah
, International Journal of Astrobiology, Vol: 10, Pages: 231-238 -
Journal articleKrasa D, Muxworthy AR, Williams W, 2011,
Room- and low-temperature magnetic properties of two-dimensional magnetite particle arrays
, Geophysical Journal International, Vol: 185, Pages: 167-180 -
Journal articleMuxworthy AR, Heslop D, Paterson GA, et al., 2011,
A Preisach method to estimate absolute paleofield intensity under the constraint of using only isothermal measurements: 2. experimental testing
, Journal of Geophysical Research, Vol: 116 -
Journal articleMuxworthy AR, Heslop D, 2011,
A Preisach method to estimate absolute paleofield intensity under the constraint of using only isothermal measurements: 1. theoretical framework
, Journal of Geophysical Research, Vol: 116 -
Book chapterSephton MA, 2011,
Meteoritics
, Encyclopedia of Geobiology, Editors: Reitner, Thiel, Publisher: Springer Verlag, Pages: 568-574, ISBN: 9781402092114The Encyclopedia of Geobiology is designed as a key reference for students, researchers,teachers, and the informed public to provide basic, but comprehensible ...
-
Journal articleMarlow JJ, Martins Z, Sephton MA, 2011,
Organic host analogues and the search for life on Mars
, INT J ASTROBIOL, Vol: 10, Pages: 31-44, ISSN: 1473-5504Mars analogue sites represent vital tools in our continued study of the Red Planet; the similar physico-chemical processes that shape a given analogue environment on Earth allow researchers to both prepare for known Martian conditions and uncover presently unknown relationships. This review of organic host analogues – sites on Earth that mimic the putatively low organic content of Mars – examines specific locations that present particular Mars-like obstacles to biological processes. Low temperatures, aridity, high radiation and oxidizing soils characterise modern-day Mars, while acid–saline waters would have presented their own challenges during the planet's warmer and wetter past. By studying each of these hurdles to life on Earth, scientists can prepare instruments headed for Mars and identify the best locations and approaches with which to look for biological signatures. As our use of organic host analogues becomes increasingly sophisticated, researchers will work to identify terrestrial sites exhibiting multiple Mars-like conditions that are tailored to the distinct mineralogical and physical characteristics of Martian locations. Making use of organic host analogues in these ways will enhance the search for signs of past or present life on Mars.
-
Journal articleWuennemann K, Collins GS, Weiss R, 2010,
IMPACT OF A COSMIC BODY INTO EARTH'S OCEAN AND THE GENERATION OF LARGE TSUNAMI WAVES: INSIGHT FROM NUMERICAL MODELING
, REVIEWS OF GEOPHYSICS, Vol: 48, ISSN: 8755-1209- Author Web Link
- Open Access Link
- Cite
- Citations: 32
-
Journal articleArnold T, Schoenbaechler M, Rehkaemper M, et al., 2010,
Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil
, Analytical and Bioanalytical Chemistry, Vol: 398, Pages: 3115-3125, ISSN: 1618-2650Analysis of naturally occurring isotopic variationsis a promising tool for investigating Zn transport andcycling in geological and biological settings. Here, wepresent the recently installed double-spike (DS) techniqueat the MAGIC laboratories at Imperial College London.The procedure improves on previous published DS methodsin terms of ease of measurement and precisions obtained.The analytical method involves addition of a 64Zn–67Zndouble-spike to the samples prior to digestion, separation ofZn from the sample matrix by ion exchange chromatography,and isotopic analysis by multiple-collector inductivelycoupled plasma mass spectrometry. The accuracy andreproducibility of the method were validated by analysesof several in-house and international elemental referencematerials. Multiple analyses of pure Zn standard solutionsconsistently yielded a reproducibility of about ±0.05‰(2 SD) for δ66Zn, and comparable precisions were obtainedfor analyses of geological and biological materials. Highlyfractionated Zn standards analyzed by DS and standardsample bracketing yield slightly varying results, whichprobably originate from repetitive fractionation eventsduring manufacture of the standards. However, the δ66Znvalues (all reported relative to JMC Lyon Zn) for two lessfractionated in-house Zn standard solutions, Imperial Zn(0.10±0.08‰: 2 SD) and London Zn (0.08±0.04‰), arewithin uncertainties to data reported with different massspectrometric techniques and instruments. Two standardreference materials, blend ore BCR 027 and ryegrass BCR281, were also measured, and the δ66Zn were found to be0.25±0.06‰ (2 SD) and 0.40±0.09‰, respectively. Takentogether, these standard measurements ascertain that thedouble-spike methodology is suitable for accurate andprecise Zn isotope analyses of a wide range of naturalsamples. The newly installed technique was consequentlyapplied to soil samples and soil
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.