Contribuer à comprendre l’origine de la vie terrestre
DESCRIPTIF DU TRAVAIL DE RECHERCHE
L’exobiologie (aussi appelée astrobiologie par les anglo-saxons) est une science ayant pour objet l’étude des facteurs et processus, notamment géochimiques et biochimiques, pouvant mener à l’apparition de la vie et à son évolution. Ceci s’applique aussi bien à l’émergence de la vie sur terre, il y a plus de 4 milliards d’années, qu’à la possibilité d’une vie ailleurs dans le système solaire. Elle s’attache à rechercher d’éventuels processus présidant à l’évolution de la matière organique simple (biomolécules) vers des structures plus complexes (premières cellules, premiers systèmes génétiques…) et à étudier les premières traces de vie terrestre et leur évolution ainsi que d’éventuelles traces de vie sur d’autres objets célestes.
Les travaux du groupe d’exobiologie portent sur les thèmes suivants :
l’origine des briques de la vie et l’origine de l’homochiralité du vivant,
l’environnement géologique à l’origine de la vie et la recherche de traces de vie dans des sédiments terrestres très anciens,
la recherche d’une vie passée et actuelle sur Mars.
1) Formation des briques de la vie
Les molécules organiques synthétisées dans l’espace ont-elles conduit à l’émergence du vivant sur la Terre prébiotique il y a plus de 4 milliards d’années ? Pour répondre à cette question, notre groupe étudie l’hypothèse que la matière organique a été importée de l’espace par les météorites ou les micrométéorites. Pour ce faire, il étudie la stabilité des acides aminés aux conditions de l’espace et à l’impact météoritique. Le groupe a collaboré avec le NASA-Johnson Space Center de Houston sur un projet de simulation d’impacts météoritiques et est actuellement impliquée dans les expériences EXPOSE-R et EXPOSE-Eutef qui ont lieu sur la Station Spatiale Internationale (ISS). Différentes expériences d’irradiation en laboratoire sont de plus mises en œuvre dans le but d’étudier l’effet du rayonnement VUV sur des acides aminés et dipeptides.
2) La Terre primitive et les premières traces de vie
Des études pluridisciplinaires, coordonnées par F. Westall, sont menées en collaboration avec plusieurs groupes français et étrangers afin d’analyser les traces de vie microbienne dans les sédiments les plus anciens (3,5 milliards d’années). Ces travaux permettent d’acquérir une meilleure connaissance de l’évolution de la vie à cette période. Des fossilisations expérimentales de microorganismes qui auraient pu vivre sur la Terre primitive (extrêmophiles) sont réalisées en parallèle afin de mieux comprendre le processus de fossilisation de ces organismes primitifs (collaboration avec l’ ISTO d’Orléans et le LMEE de Brest).
Afin de mener à bien ces études, des méthodes d’analyses poussées sont mises en œuvre : la spectroscopie Raman et IR, et la microscopie à force atomique (CBM, Orléans), les microscopies électroniques à balayage en transmission (Université d’Orléans), la préparation de coupes ultrafines au FIB (IEMN, Lille), la microscopie aux rayons X et la micro-XANES (ESRF, Grenoble et AIFIRA, Bordeaux), la NanoSIMS (MNHN, Paris) et la SIMS (CRPG, Nancy).
3) La recherche de traces de vie sur Mars
Afin d’étudier des traces d’une vie passée sur Mars il existe plusieurs solutions dans lesquelles nous sommes impliqués : réaliser des analyses in situ (mission ExoMars en 2018), rapporter des échantillons sur Terre (mission Mars Sample Return, MSR, 2022) ou analyser des météorites sédimentaires.
Notre groupe est à l’origine d’un des instruments qui équiperont le robot Pasteur de la mission européenne ExoMars : le close-up imager (jouant le rôle de la loupe du géologue). Nous sommes également impliqués dans la réflexion sur la coopération entre les deux rovers, ExoMars (ESA) et Max-C (NASA) dans la nouvelle configuration de la mission martienne internationale pour 2018. Enfin, nous travaillons également sur la constitution d’une lithothèque de roches analogues de Mars en collaboration avec l’Observatoire des Sciences de l’Univers en région Centre (OSUC, Orléans), permettant de tester les futurs dispositifs spatiaux et de faciliter l’interprétation des analyses in situ. Cette collection de roches et sa base données associée aideront à sélectionner les échantillons à prélever en vue de leur retour sur Terre, lors de la future mission MSR, et à élaborer les protocoles expérimentaux à mettre en œuvre pour leur analyse.
Sous la direction du Groupe d’Exobiologie (Orléans), les expériences spatiales STONE-5 et STONE-6 ont été réalisées afin de tester la survie éventuelle de sédiments martiens (toutes les météorites martiennes découvertes à ce jour étant d’origine volcanique). Des météorites artificielles analogues de sédiments martiens, dont certains contenaient des microfossiles de 3,5 milliards d’années, ont été soumises à l’entrée dans l’atmosphère terrestre. Il a été démontré que les météorites sédimentaires martiennes pouvaient survivre à l’entrée atmosphérique. L’expérience STONE-6 a également prouvé que d’hypothétiques traces de vie fossile pourraient y être retrouvées. Enfin, des bactéries cryptoendolithiques vivantes ont été placées à l’arrière de ces météorites afin de tester l’hypothèse de la panspermie. Elles ont été retrouvées carbonisées, démontrant qu’une couche de plusieurs centimètres, estimée par modélisation à 5 cm, aurait été nécessaire à leur survie.
Des expériences liées aux trois thématiques principales sont poursuivies avec :
- l’exposition de molécules organiques à bord de la Station Spatiale Internationale ou par simulations au sol,
- l’analyse des molécules organiques dans des comètes,
- la recherche de biosignatures de la vie fossile et l’étude de l’évolution de la vie à travers les signatures dans les roches,
- la fossilisation artificielle de macromolécules prébiotiques, de bactéries extrêmophiles et de virus,
- La constitution d’une lithothèque de roches modèles des roches de Mars et d’une base de données permettant de tester des instruments spatialisés et d’être utilisée lors des missions in situ,
- La recherche de traces de vie martienne par des missions in situ et de retour d’échantillons martiens.
• Foucher F. ; Westall F. ; Brandstätter F. ; Demets R. ; Parnell J. ; Cockell C. S. ; Edwards H. G. M. ; Bény J.-M. and Brack A. Testing the survival of microfossils in martian sedimentary meteorites during Earth’s atmospheric entry : the STONE 6 experiment. (2010) Icarus 207, 616-630.
• Orange F. ; Westall F. ; Disnar J. R. ; Prieur D. ; Bienvenu N. ; Leromancer M. ; Defarge C. Experimental silicification of the extremophilic Archaea Pyrococcus abyssi and Methanocaldococcus jannaschii : applications in the search for evidence of life in early Earth and extraterrestrial rocks (2009) Geobiology 7, 403-418
• Bertrand M., Van der Gaast S., Vilas F., Hörz F., Haynes G., Chabin A., Brack A. and Westall F The fate of Amino Acids during simulated Meteoritic Impact (2009) Astrobiology, Vol.9, 10, 943-951.
• Bertrand, M., Chabin, A., Brack, A., Westall, F. Separation of amino acid enantiomers via chiral derivitization and non-chiral gas chromatography. (2008) J. Chromatography, 1180, 131-137.
• Brack, A. From interstellar amino acids to prebiotic catalytic peptides Chem. Biodivers. (2007) 4 665-679
• Lemelle, L ; Labrot, P ; Salomé, M ; Simionovici, A ; Viso, M ; Westall, F. In situ imaging of organic sulfur in 700-800 My-old Neoproterozoic microfossils by X-ray spectromicroscopy at the S K-edge Org. Geochem. (2007) 39 188-202
• Pullan, D ; Westall, F ; Hofmann, BA ; Parnel, J ; Cockell, CS ; Edwards, HGM ; Jorge Villar, SE ; Schröder, C ; Cressey, G ; Marinangeli, L ; Richter, L ; Klingelhöfer, G Identification of morphological biosignatures in martian analog field specimens using in situ planetary instrumentation : an integrated approach Astrobiology (2007) 1180 131-137
• Westall, F ; De Ronde, CEJ ; Southam, G ; Grassineau, N ; Colas, M ; Cockell, C ; Lammer, H Implications of a 3.472-3.333 Ga-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early Earth. Phil. Trans. Roy. Soc. Lond. Series B (2006) 361 1857–1875
• Westall, F Life on the early Earth : a sedimentary view Science (2005) 308 (5720) 366-367
• Munoz Caro, GM ; Meierhenrich, JJ ; Schutte, WA ; Barbier, B ; Arcones Segovia, A ; Rosenbauer, H ; Thiemann, WHP ; Brack, A ; Greenberg, JM Amino acids from ultraviolet irradiation of interstellar ice analogues Nature (2002) 416 403 - 406
Principales techniques employées
- Analyse de molécules organiques par chromatographie gazeuse ou liquide
- Fossilisation de bactéries, virus et macromolécules
- Mise au point de méthodes d’analyses de microfossiles inclus dans des roches en faisant appel aux techniques suivantes :
- Microscopie optique
- Microscopie à force atomique
- Spectrométrie Raman et IR
- Microscopie électronique à balayage et à transmission
- Réalisation de coupes FIB (IEMN, Lille)
- Microscopie aux rayons X (ESRF-Grenoble, AIFIRA, Bordeaux)
- XANES (ESRF-Grenoble)
- NanoSIMS (MNHN-Paris)
- SIMS (CRPG-Nancy)
Principaux équipements utilisés
- Chromatographe phase gazeuse couplée à un spectromètre de masse (GC-MS)
- Chromatographie liquide haute performance analytique et préparative (HPLC)
- Spectromètre Raman couplé avec un microscope à force atomique
- Spectromètre IR
- Microscope à force atomique
- Microscope optique
- Chambre d’irradiation reproduisant les conditions de vide et d’irradiation de l’espace.
Voir les légendes :
- Figure 1 : Image AFM d’un microfossile dans une roche.
Figure 2 : Image par microscopie électronique à balayage de microfossiles dans des roches datant de 3.5 milliards d’années.
Figure 3 : Image en microscopie électronique à balayage de micro-organismes fossilisés expérimentalement.
Figure 4 : EXPOSE-R sur la Station Spatiale Internationale (ISS).
Figure 5 : Cartographie Raman tridimensionnelle de microfossiles dans une roche.
Membres du groupe thématique
Schwenzer S. P., Bridges J.-C., Wiens R. C., Conrad P. G., Kelley S. P., Leveille R., Mangold N., Martín-Torres J., McAdam A., Newsom H., Paz Zorzano M., Rapin W., Spray J., Treiman A.H., Westall F. and Fairen A. (2016)
The Raman-derived carbonization continuum : a tool to select the best preserved molecular structures in Archean kerogensAstrobiology (sous presse) Cottin H. and 29 authors incl. Westall F. (2016)
Space as a Tool for Astrobiology : review and recommendations for experimentations in Earth orbit and beyondSpace Science Reviews (sous presse) Rettberg P., Anesio A. M., Baker V. R., Baross J. A., Cady S. L., Detsis E., Foreman C. M., Hauber E., Ori G. G., Pearce D. A., Renno N. O., Ruvkun G., Sattler B., Saunders M. P., Smith, David H., Wagner D. and Westall F. (2016)
We highlight the role of COSPAR and the scientific community in defining and updating the framework of planetary protection. Specifically, we focus on Mars ?Special Regions, ? areas where strict planetary protection measures have to be applied before a spacecraft can explore them, given the existence of environmental conditions that may be conducive to terrestrial microbial growth. We outline the history of the concept of Special Regions and inform on recent developments regarding the COSPAR policy, namely, the MEPAG SR-SAG2 review and the Academies and ESF joint committee report on Mars Special Regions. We present some new issues that necessitate the update of the current policy and provide suggestions for new definitions of Special Regions. We conclude with the current major scientific questions that remain unanswered regarding Mars Special Regions.
Gaspar V. M., Baril P., Costa E. C., de Melo-Diogo D., Foucher F., Queiroz J. A., Sousa F., Pichon C. and Correia I. J. (2015)
Bioreducible poly(2-ethyl-2-oxazoline)-PLA-PEI-SS triblock copolymer micelles for co-delivery of DNA minicircles and DoxorubicinJournal of Controlled Release (2015) 213, 175-191 - doi : 10.1016/j.jconrel.2015.07.011
The co-delivery of minicircle DNA (mcDNA) and small anti-cancer drugs via stimuli-sensitive nanocarriers is a promising approach for combinatorial cancer therapy. However, the simultaneous loading of drugs and DNA in nanosized delivery systems is remarkably challenging. In this study we describe the synthesis of triblock copolymer micelles based on poly(2-ethyl-2-oxazoline)-poly(L-lactide) grafted with bioreducible polyethylenimine (PEOz-PLA-g-PEI-SS) for co-delivery of supercoiled (sc) mcDNA vectors and Doxorubicin (Dox). These amphiphilic carriers take advantage of non-fouling oxazolines to confer biological stability, of PLA to provide a hydrophobic core for drug encapsulation and of bioreducible PEI-SS to provide mcDNA complexation and an on-demand stimuli-responsive release. The obtained results show that mcDNA-loaded micelleplexes penetrate into in vitro tumor spheroid models with specific kinetics and exhibit a higher gene expression when compared to non-bioreducible nanocarriers. Moreover, in vivo bioluminescence imaging showed that gene expression is detected up to 8days following mcDNA-micelles intratumoral administration. Furthermore, drug-gene co-delivery in PEOz-PLA-g-PEI-SS carriers was verified by successful encapsulation of both Dox and mcDNA with high efficacy. Moreover, dual-loaded micelleplexes presented significant uptake and a cytotoxic effect in 2D cultures of cancer cells. The co-delivery of mcDNA-Dox to B16F10-Luciferase tumor bearing mice resulted in a reduction in tumor volume and cancer cells viability. Overall, such findings indicate that bioreducible triblock micelles are efficient for focal delivery in vivo and have potential for future application in combinatorial DNA-drug therapy.
The Mars Science Laboratory rover Curiosity found host rocks of basaltic composition and alteration assemblages containing clay minerals at Yellowknife Bay, Gale Crater. On the basis of the observed host rock and alteration minerals, we present results of equilibrium thermochemical modeling of the Sheepbed mudstones of Yellowknife Bay in order to constrain the formation conditions of its secondary mineral assemblage. Building on conclusions from sedimentary observations by the Mars Science Laboratory team, we assume diagenetic, in situ alteration. The modeling shows that the mineral assemblage formed by the reaction of a CO2-poor and oxidizing, dilute aqueous solution (Gale Portage Water) in an open system with the Fe-rich basaltic-composition sedimentary rocks at 10–50°C and water/rock ratio (mass of rock reacted with the starting fluid) of 100–1000, pH of 7.5–12. Model alteration assemblages predominantly contain phyllosilicates (Fe-smectite, chlorite), the bulk composition of a mixture of which is close to that of saponite inferred from Chemistry and Mineralogy data and to that of saponite observed in the nakhlite Martian meteorites and terrestrial analogues. To match the observed clay mineral chemistry, inhomogeneous dissolution dominated by the amorphous phase and olivine is required. We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component.
The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is the concept of habitability, the set of conditions that allows the appearance of life and successful establishment of microorganisms in any one location. While environmental conditions may have been conducive to the appearance of life early in martian history, habitable conditions were always heterogeneous on a spatial scale and in a geological time frame. This "punctuated" scenario of habitability would have had important consequences for the evolution of martian life, as well as for the presence and preservation of traces of life at a specific landing site. We hypothesize that, given the lack of long-term, continuous habitability, if martian life developed, it was (and may still be) chemotrophic and anaerobic. Obtaining nutrition from the same kinds of sources as early terrestrial chemotrophic life and living in the same kinds of environments, the fossilized traces of the latter serve as useful proxies for understanding the potential distribution of martian chemotrophs and their fossilized traces. Thus, comparison with analog, anaerobic, volcanic terrestrial environments (Early Archean >3.5-3.33 Ga) shows that the fossil remains of chemotrophs in such environments were common, although sparsely distributed, except in the vicinity of hydrothermal activity where nutrients were readily available. Moreover, the traces of these kinds of microorganisms can be well preserved, provided that they are rapidly mineralized and that the sediments in which they occur are rapidly cemented. We evaluate the biogenicity of these signatures by comparing them to possible abiotic features. Finally, we discuss the implications of different scenarios for life on Mars for detection by in situ exploration, ranging from its non-appearance, through preserved traces of life, to the presence of living microorganisms. KEY WORDS : Mars-Early Earth-Anaerobic chemotrophs-Biosignatures-Astrobiology missions to Mars.
Multiplication of microbes below 0.690 water activity : implications for terrestrial and extraterrestrial lifeEnvironmental Microbiology (2015) 17 (2) 257-277 - doi : 10.1111/1462-2920.12598
Since a key requirement of known life forms is available water (water activity ; aw), recent searches for signatures of past life in terrestrial and extraterrestrial environments have targeted places known to have contained significant quantities of biologically available water. However, early life on Earth inhabited high-salt environments, suggesting an ability to withstand low water-activity. The lower limit of water activity that enables cell division appears to be ∼ 0.605 which, until now, was only known to be exhibited by a single eukaryote, the sugar-tolerant, fungal xerophile Xeromyces bisporus. The first forms of life on Earth were, though, prokaryotic. Recent evidence now indicates that some halophilic Archaea and Bacteria have water-activity limits more or less equal to those of X. bisporus. We discuss water activity in relation to the limits of Earth’s present-day biosphere ; the possibility of microbial multiplication by utilizing water from thin, aqueous films or non-liquid sources ; whether prokaryotes were the first organisms able to multiply close to the 0.605-aw limit ; and whether extraterrestrial aqueous milieux of ≥ 0.605 aw can resemble fertile microbial habitats found on Earth.
The International Continental Scientific Drilling Program (ICDP) has long espoused studies of deep subsurface life, and has targeted fundamental questions regarding subsurface life, including the following : “(1) What is the extent and diversity of deep microbial life and what are the factors limiting it ? (2) What are the types of metabolism/carbon/energy sources and the rates of subsurface activity ? (3) How is deep microbial life adapted to subsurface conditions ? (4) How do subsurface microbial communities affect energy resources ? And (5) how does the deep biosphere interact with the geosphere and atmosphere ?” (Horsfield et al., 2014) Many ICDP-sponsored drilling projects have included a deep-life component ; however, to date, not one project has been driven by deep-life goals, in part because geomicrobiologists have been slow to initiate deep biosphere-driven ICDP projects. Therefore, the Deep Carbon Observatory (DCO) recently partnered with the ICDP to sponsor a workshop with the specific aim of gathering potential proponents for eep-life-driven ICDP projects and ideas for candidate drilling sites. Twenty-two articipants from nine countries proposed projects and sites that included ompressional and extensional tectonic environments, evaporites, hydrocarbon-rich shales, flood basalts, Precambrian shield rocks, subglacial and subpermafrost environments, active volcano–tectonic systems, megafan deltas, and serpentinizing ultramafic environments. The criteria and requirements for successful ICDP applications were presented. Deep-life-specific technical requirements were discussed and it was concluded that, while these procedures require adequate planning, they are entirely compatible with the sampling needs of other disciplines. As a result of this workshop, one drilling workshop proposal on the Basin and Range Physiographic Province (BRPP) has been submitted to the ICDP, and several other drilling project proponents plan to submit proposals for ICDP-sponsored drilling workshops in 2016.
Photochemical studies in low Earth orbit for organic compounds related to small bodies, Titan and Mars. Current and future facilities.Bulletin de la Société Royale des Sciences de Liège (2015) 84, 60-73
The study of the evolution of organic matter subjected to space conditions, and more specifically to solar photons in the vacuum ultraviolet range (120-200 nm) has been undertaken in low Earth Orbit since the 90’s, and implemented on various space platforms. The most recent exposure facilities are BIOPAN outside the Russian automatic capsules FOTON, and EXPOSE-E & -R (1&2) outside the International Space Station. They allow the photolysis of many different samples simultaneously, and provide us with valuable data about the formation and evolution of organic matter in the Solar System (meteorites, comets, Titan’s atmosphere, the Martian surface...) and in the Interstellar Medium. They have been used by European teams in the recent past(ORGANIC on BIOPAN V-FOTON M2 and UVolution on BIOPAN VI-FOTON M3, PROCESS on EXPOSE-E, AMINO and ORGANICS on EXPOSE-R), and a new EXPOSE set is currently exposed outside the ISS (PSS on EXPOSE-R2). These existing tools are very valuable ; however, they have significant limitations that limit their capabilities and scientific return. One of the most critical issues for current studies is the lack of any in-situ analysis of the evolution of the samples as a function of time. Only two measurements are available for the experiment : one before and one after the exposure. A significant step forward has been achieved with the O/OREOS NASA nanosatellite and the OREOcube ESA project with onboard UV-visible measurements. However, for organic samples, following the evolution of the samples would be more informative and provide greater insight with infrared measurements, which display specific patterns characteristic of major organic functionalities in the mid-infrared range (4000-1000 cm-1).
Interacting, diverse microbe-sediment systems exist in natural environments today but have not yet been recognized in the oldest records of life on Earth (older than 3.3 Ga) because of lack of distinctive biomarker molecules and patchy preservation of microbial paleocommunities. In an in-situ outcrop- to microbial-scale study, we have differentiated probable phototrophic, chemolithotrophic, and chemo-organotrophic fossil microbial signatures in a nearshore volcanogenic sedimentary setting in 3.33 Ga rocks of the Josefsdal Chert, Barberton greenstone belt, South Africa, while demonstrating the importance of contemporaneous hydrothermal activity. Hydrothermal fluids, as a nutrient source, strongly controlled the development and distribution of the microbial communities and, as a silicifying agent, contributed to their rapid fossilization. We thus show that intricate microbe-sediment systems are deep-rooted in time and that at least some early life may indeed have been thermophilic.
Revealing the biotic origin of silicified Precambrian carbonaceous microstructures using Raman spectroscopic mapping, a potential method for the detection of microfossils on MarsJournal of Raman Spectroscopy (2015) First published online : 2015, 14 apr - doi : 10.1002/jrs.4687
Demonstrating the biogenicity of carbonaceous microfossils can be relatively difficult because of their small size and simple shape, and to the degradation of the associated organic molecules with time. For Precambrian fossils, it generally requires the use of several techniques to study the shape and the composition of the structure itself, as well as its mineral environment. The ability to identify both organic matter and minerals using Raman spectroscopy makes it a key technique in the field of micropaleontology. Raman instruments are also being developed for the upcoming missions to Mars, ExoMars and Mars 2020, both dedicated to the search for past or present traces of life. However, demonstrating the biotic origin of carbonaceous matter in geological materials using this technique is controversial. Here, we show that Raman mapping instead of single spot analysis can detect variations in the composition of carbonaceous matter associated with fossilized microbes in the 800-Ma-old microfossils from the Draken Formation, Svalbard. This discovery is of great interest because it permits assessment of the biotic origin of a fossilized carbonaceous structure. Raman mapping could thus be of crucial importance in the near future for detecting potential fossilized microbial remains in Martian rocks.
Geyserite in hot-spring siliceous sinter : Window on Earth’s hottest terrestrial (paleo)environment and its extreme lifeEarth-Science Reviews (2015) 148 44-64 - doi : 10.1016/j.earscirev.2015.05.009
Siliceous hot-spring deposits, or sinters, typically form in active, terrestrial (on land), volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the Earth’s surface as silica-charged geothermal fluids. Geyserites are sinters affiliated with the highest temperature ( 75–100 °C), natural geothermal fluid emissions, comprising localized, lithologically distinctive, hydrothermal silica precipitates that develop around geysers, spouters and spring-vents. They demarcate the position of hot-fluid upflow zones useful for geothermal energy and epithermal mineral prospecting. Near-vent areas also are “extreme environment” settings for the growth of microbial biofilms at near-boiling temperatures. Microbial biosignatures (e.g., characteristic silicified microbial textures, carbon isotopes, genetic material, lipid biomarkers) may be extracted from modern geyserite. However, because of strong taphonomic filtering and subsequent diagenesis, fossils in geyserite are very rare in the pre-Quaternary sinter record which, in and of itself, is patchy in time and space back to about 400 Ma. Only a few old examples are known, such as geyserite reported from the Devonian Drummond Basin (Australia), Devonian Rhynie cherts (Scotland), and a new example described herein from the spectacularly well-preserved, Late Jurassic (150 Ma), Yellowstone-style geothermal landscapes of Patagonia, Argentina. There, geyserite is associated with fossil vent-mounds and silicified hydrothermal breccias of the Claudia sinter, which is geologically related to the world-class Cerro Vanguardia gold/silver deposit of the Deseado Massif, a part of the Chon Aike siliceous large igneous province. Tubular, filament-like micro-inclusions from Claudia were studied using integrated petrographic and laser micro-Raman analysis, the results of which suggest a biological origin. The putative fossils are enclosed within nodular geyserite, a texture typical of subaerial near-vent conditions. Overall, this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of Earth’s highest temperature, habitable terrestrial sedimentary environment. Hot-spring depositional settings also may serve as analogs for early Earth paleoenvironments because of their elevated temperature of formation, rapid mineralization by silica, and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures.
Testing the ability of the ExoMars 2018 payload to document geological context and potential habitability on MarsPlanetary and Space Science (2015) 108 87-97 - doi : 10.1016/j.pss.2015.01.006
The future ExoMars rover mission (ESA/Roscosmos), to be launched in 2018, will investigate the habitability of the Martian surface and near subsurface, and search for traces of past life in the form of textural biosignatures and organic molecules. In support of this mission, a selection of relevant Mars analogue materials has been characterised and stored in the International Space Analogue Rockstore (ISAR), hosted in Orléans, France. Two ISAR samples were analysed by prototypes of the ExoMars rover instruments used for petrographic study. The objective was to determine whether a full interpretation of the rocks could be achieved on the basis of the data obtained by the ExoMars visible-IR imager and spectrometer (MicrOmega), the close-up imager (CLUPI), the drill infrared spectrometer (Ma_Miss) and the Raman spectrometer (RLS), first separately then in their entirety. In order to not influence the initial instrumental interpretation, the samples were sent to the different teams without any additional information. This first step was called the “Blind Test” phase. The data obtained by the instruments were then complemented with photography of the relevant outcrops (as would be available during the ExoMars mission) before being presented to two geologists tasked with the interpretation. The context data and photography of the outcrops and of the samples were sufficient for the geologists to identify the rocks. This initial identification was crucial for the subsequent, iterative interpretation of the spectroscopic data. The data from the different spectrometers was, thus, cross-calibrated against the photographic interpretations and against each other. In this way, important mineralogical details, such as evidence of aqueous alteration of the rocks, provided relevant information concerning potential habitable conditions. The final conclusion from this test is that, when processed together, the ExoMars payload instruments produce complementary data allowing reliable interpretation of the geological context and potential for habitable environments. This background information is fundamental for the analysis and interpretation of organics in the processed Martian rocks.
Expose is a multi-user instrument for astrobiological and astrochemical experiments in space. Installed at the outer surface of the International Space Station, it enables investigators to study the impact of the open space environment on biological and biochemical test samples. Two Expose missions have been completed so far, designated as Expose-E (Rabbow et al. 2012) and Expose-R (Rabbow et al. this issue). One of the space-unique environmental factors offered by Expose is full-spectrum, ultraviolet (UV)-rich electromagnetic radiation from the Sun. This paper describes and analyses how on Expose-R, access of the test samples to Solar radiation degraded during space exposure in an unpredicted way. Several windows in front of the Sun-exposed test samples acquired a brown shade, resulting in a reduced transparency in visible light, UV and vacuum UV (VUV). Post-flight investigations revealed the discolouration to be caused by a homogenous film of cross-linked organic polymers at the inside of the windows. The chemical signature varied per sample carrier. No such films were found on windows from sealed, pressurized compartments, or on windows that had been kept out of the Sun. This suggests that volatile compounds originating from the interior of the Expose facility were cross-linked and photo-fixed by Solar irradiation at the rear side of the windows. The origin of the volatiles was not fully identified ; most probably there was a variety of sources involved including the biological test samples, adhesives, plastics and printed circuit boards. The outer surface of the windows (pointing into space) was chemically impacted as well, with a probable effect on the transparency in VUV. The reported analysis of the window contamination on Expose-R is expected to help the interpretation of the scientific results and offers possibilities to mitigate this problem on future missions – in particular Expose-R2, the direct successor of Expose-R.
The AMINO experiment : exposure of amino acids in the EXPOSE-R experiment on the International Space Station and in laboratoryInternational Journal of Astrobiology (2015) 14 (1) 89-97 - doi : 10.1017/S1473550414000354
In order to confirm the results of previous experiments concerning the chemical behaviour of organic molecules in the space environment, organic molecules (amino acids and a dipeptide) in pure form and embedded in meteorite powder were exposed in the AMINO experiment in the EXPOSE-R facility onboard the International Space Station. After exposure to space conditions for 24 months (2843 h of irradiation), the samples were returned to the Earth and analysed in the laboratory for reactions caused by solar ultraviolet (UV) and other electromagnetic radiation. Laboratory UV exposure was carried out in parallel in the Cologne DLR Center (Deutsches Zentrum für Luft und Raumfahrt). The molecules were extracted from the sample holder and then (1) derivatized by silylation and analysed by gas chromatography coupled to a mass spectrometer (GC–MS) in order to quantify the rate of degradation of the compounds and (2) analysed by high-resolution mass spectrometry (HRMS) in order to understand the chemical reactions that occurred. The GC–MS results confirm that resistance to irradiation is a function of the chemical nature of the exposed molecules and of the wavelengths of the UV light. They also confirm the protective effect of a coating of meteorite powder. The most altered compounds were the dipeptides and aspartic acid while the most robust were compounds with a hydrocarbon chain. The MS analyses document the products of reactions, such as decarboxylation and decarbonylation of aspartic acid, taking place after UV exposure. Given the universality of chemistry in space, our results have a broader implication for the fate of organic molecules that seeded the planets as soon as they became habitable as well as for the effects of UV radiation on exposed molecules at the surface of Mars, for example.
Gaboyer F., Burgaud G. and Alain K. (2014)
Physiological and evolutionary potential of microorganisms from the Canterbury Basin subseafloor, a metagenomic approachFems Microbiology Ecology (2014) 91 (5) 13 - doi : 10.1093/femsec/fiv029
Subseafloor sediments represent a large reservoir of organic matter and are inhabited by microbial groups of the three domains of life. Besides impacting the planetary geochemical cycles, the subsurface biosphere remains poorly understood, notably questions related to possible metabolic pathways and selective advantages that may be deployed by buried microorganisms (sporulation, response to stress, dormancy). In order to better understand physiological potentials and possible lifestyles of subseafloor microbial communities, we analyzed two metagenomes from subseafloor sediments collected at 31 mbsf (meters below the sea floor) and 136 mbsf in the Canterbury Basin. Metagenomic phylogenetic and functional diversities were very similar. Phylogenetic diversity was mostly represented by Chloroflexi, Firmicutes and Proteobacteria for Bacteria and by Thaumarchaeota and Euryarchaeota for Archaea. Predicted anaerobic metabolisms encompassed fermentation, methanogenesis and utilization of fatty acids, aromatic and halogenated substrates. Potential processes that may confer selective advantages for subsurface microorganisms included sporulation, detoxication equipment or osmolyte accumulation. Annotation of genomic fragments described the metabolic versatility of Chloroflexi, Miscellaneous Crenarchaeotic Group and Euryarchaeota and showed frequent recombination events within subsurface taxa. This study confirmed that the subseafloor habitat is unique compared to other habitats at the (meta)-genomic level and described physiological potential of still uncultured groups.
Experimental fossilization of the Thermophilic Gram-positive Bacterium Geobacillus SP7A : A Long Duration Preservation StudyGeomicrobiology Journal (2014) 31 (7) 578-589 - doi : 10.1080/01490451.2013.860208
Recent experiments to fossilize microorganisms using silica have shown that the fossilization process is far more complex than originally thought ; microorganisms not only play an active role in silica precipitation but may also remain alive while silica is precipitating on their cell wall. To better understand the mechanisms that lead to the preservation of fossilized microbes in recent and ancient rocks, we experimentally silicified a Gram-positive bacterium, Geobacillus SP7A, over a period of five years. The microbial response to experimental fossilization was monitored with the use of LIVE/DEAD staining to assess the structural integrity of the cells during fossilization. It documented the crucial role of silicification on the preservation of the cells and of their structural integrity after several years. Electron microscopy observations showed that initial fossilization of Gram-positive bacteria was extremely rapid, thus allowing very good preservation of Geobacillus SP7A cells. A thick layer of silica was deposited on the outer surface of cell walls in the earliest phase of silicification before invading the cytoplasmic space. Eventually, the cell wall was the only recognizable feature. Heavily mineralized cells thus showed morphological similarities with natural microfossils found in the rock record.
The question of whether there is or was life on Mars has been one of the most pivotal since Schiaparellis’ telescopic observations of the red planet. With the advent of the space age, this question can be addressed directly by exploring the surface of Mars and by bringing samples to Earth for analysis. The latter, however, is not free of problems. Life can be found virtually everywhere on Earth. Hence the potential for contaminating the Mars samples and compromising their scientific integrity is not negligible. Conversely, if life is present in samples from Mars, this may represent a potential source of extraterrestrial biological contamination for Earth. A range of measures and policies, collectively termed ‘planetary protection’, are employed to minimise risks and thereby prevent undesirable consequences for the terrestrial biosphere. This report documents discussions and conclusions from a workshop held in 2012, which followed a public conference focused on current capabilities for performing life-detection studies on Mars samples. The workshop focused on the evaluation of Mars samples that would maximise scientific productivity and inform decision making in the context of planetary protection. Workshop participants developed a strong consensus that the same measurements could be employed to effectively inform both science and planetary protection, when applied in the context of two competing hypotheses : 1) that there is no detectable life in the samples ; or 2) that there is martian life in the samples. Participants then outlined a sequence for sample processing and defined analytical methods that would test these hypotheses. They also identified critical developments to enable the analysis of samples from Mars.
Metazoans (multicellular animals) evolved during the Ediacaran Period as shown by the record of their imprints, carbonaceous compressions, trace fossils, and organic bodies and skeletal fossils. Initial evolutionary experiments produced unusual bodies that are poorly understood or conceived of as non-metazoan. It is accepted that sponges, ctenophorans, cnidarians, placozoans, and bilaterians were members of the Ediacaran fauna, many of which have uncertain affinities. The fossil Sabellidites cambriensis Yanishevsky, 1926, derived from the terminal Ediacaran strata, is the earliest known organically preserved animal that belonged to a newly evolving fauna, which replaced the Ediacara-type metazoans. Morphologically simple soft-bodied tubular fossils, such as S. cambriensis, and biomineralized, as contemporaneous Sinotubulites sp., are not easy to recognize phylogenetically because many unrelated organisms developed encasing tubes independently. Therefore, in addition to morphologic information, evidence derived from the microstructure of the organic wall and its biochemistry may be vital to resolving fossil origins and phylogenetic relationships. Here we present morphological, microstructural and biogeochemical studies on S. cambriensis using various microscopic and spectroscopic techniques, which provide new evidence that supports its siboglinid, annelidan affinity. The late Ediacaran age of Sabellidites fossil constrains the minimum age of siboglinids and the timing of the divergence of including them annelids by fossil record and this could be tested using molecular clock estimates. The fine microstructure of the organic tube in Sabellidites is multi-layered and has discrete layers composed of differently orientated and perfectly shaped fibers embedded in an amorphous matrix. The highly ordered and specific pattern of fiber alignment (i.e., the texture of organic matter) is similar to that of representatives of the family Siboglinidae. The biogeochemistry of the organic matter that comprised the tube, which was inferred from its properties, composition, and microstructure, is consistent with chitin and proteins as in siboglinids.
Cherts of the Barberton Greenstone Belt, South Africa : Petrology and Trace-element Geochemistry of 3.5 to 3.3 Ga Old Silicified Volcaniclastic SedimentsSouth African Journal of Geology 116 (2) 297-322 - doi : 10.2113/gssajg.116.2.297
A suite of green and carbonaceous black chert interbedded with submarine volcanic rocks from several stratigraphic levels of the Onverwacht Group of the Barberton greenstone belt, from the top of the 3.48 Ga Komati Formation to the base of the 3.26 Ga Fig Tree Group have been investigated petrologically and geochemically. Provenance analysis was undertaken using immobile trace element ratios in comparison with potential source rocks from the Barberton granitoid-greenstone terrain. Raman spectroscopy was used to better characterise carbonaceous matter in different chert varieties. Green cherts consist predominantly of silicified mafic to ultramafic volcaniclastic material. Black cherts contain volcaniclastic and/or epiclastic material of ultramafic to felsic composition, admixed with carbonaceous matter. In several cases, the clastic sediment is compositionally distinct to the volcanic substrate, suggesting that it represents volcanic material of relatively distal sources. Soon after settling out of the water column, lithification due to silicification took place. It gave rise to excellent textural preservation, but strongly modified the mineralogical and chemical composition of the seafloor sediments. Zircon, Cr-spinel and rare phosphate minerals are the only primary minerals remaining, while clastic grains have been largely replaced by a fine intergrowth of microquartz, Ti-oxide and K-bearing mica. Chemical changes are similar to those reported previously for silicification of volcanic rocks from the barberton belt and are consistent with low-temperature hydrothermal processes common to the Palaeoarchaean seafloor environment.
Ossa, F.O., El Albani, A., Hofmann, A., Bekker, A., Gauthier-Lafaye, F., Pambo, F., Meunier, A., Fontaine, C., Boulvais, P., Pierson-Wickmann, A.C., Cavalazzi, B., Macchiarelli, R. (2013)
Exceptional preservation of expandable clay minerals in the ca. 2.1 Ga black shales of the Francevillian basin, Gabon and its implication for atmospheric oxygen accumulationChemical Geology (2013) 362 (SI) 181-192 - doi : 10.1016/j.chemgeo.2013.08.011
Clay minerals are exceptionally well preserved in marine black shale of the ca. 2.1 Ga Francevillian Group in southeastern Gabon. The FB Formation of the Francevillian Group is characterized by smectite-rich clay minerals including randomly ordered (R0-type) and ordered (R1-type) mixed layer illite/smectite (I/S). The preservation of R0-type clay minerals suggests unexpectedly slow mineral transformation and a moderate degree of diagenesis, which is unique, considering the Paleoproterozoic age of the sedimentary rocks. R0- and R1-type, smectite-rich particles occur in stratigraphic intervals with high organic carbon content and are associated with carbonaceous filamentous structures, suggesting formation of clay-organic matter complexes. Our data suggests that clay minerals may have enhanced organic matter preservation, providing the oldest example where a link between clay minerals and organic matter sequestration can be established. Our findings are consistent with the hypothesis that clay minerals enhanced organic carbon burial and aided in atmospheric oxygen accumulation through time
The Raman Laser Spectrometer (RLS) is part of the payload of the 2018 ExoMars rover. The Sample Preparation and Distribution System (SPDS) of the rover will crush samples acquired from down to two meters depth under the Martian surface, and provide them to the RLS instrument in the form of flattened powdered samples. The RLS instrument will acquire a minimum of 20 points on the flattened surface of the samples. To be able to obtain the maximum scientific return from the instrument once on Mars, a simulator of the SPDS system has been built to perform a series of experiments in a representative scenario. The crushing process implies the loss of rock structure and texture and, hence, the geological context of the samples. However, qualitative analysis with the RLS simulator on powdered natural samples and rocks showed that the RLS is capable of detecting carbonaceous material occurring in trace amounts in one of the rock samples (a silicified volcanic sand), more easily than with the same analysis on bulk. Furthermore, it is shown that minor phases in carbonate cements that cannot be detected by Raman in the bulk sample can be detected in the powder, thus allowing the identification of all the carbonate phases present in the cement crust.
In order to quantify the detection threshold of the instrument, further analysis on controlled samples were performed. The results with the RLS SPDS simulator showed that the instrument can reach detection thresholds down to 1 % on powdered samples. Furthermore, analysis of controlled mixtures showed that performing a very simple intensity-based statistical analysis of the spectra can provide semi-quantification of the abundance of the mineral species with quite linear calibration curves.
Abstract Extraterrestrial habitability is a complex notion. We briefly review what is known about the origin of life on Earth, that is, life based on carbon chemistry and water. We then discuss habitable conditions (past and present) for established life and for the survival of microorganisms. Based on these elements, we propose to use the term habitable only for conditions necessary for the origin of life, the proliferation of life, and the survival of life. Not covered by this term would be conditions necessary for prebiotic chemistry and conditions that would allow the recognition of extinct or hibernating life. Finally, we apply this concept to the potential emergence of life on Mars where suitable conditions for life to start, proliferate, and survive have been heterogeneous throughout its history. These considerations have a profound impact on the nature and distribution of eventual traces of martian life, or any precursor, and must therefore inform our search-for-life strategies.
Missions to Mars : Characterisation of Mars analogue rocks for the International Space Analogue Rockstore (ISAR)Planetary and Space Science. 82-83, 113-127
Instruments for surface missions to extraterrestrial bodies should be cross-calibrated using a common suite of relevant materials. Such work is necessary to improve instrument performance and aids in the interpretation of in-situ measurements. At the CNRS campus in Orléans, the Observatoire des Sciences de l’Univers en région Centre (OSUC) has created a collection of well-characterised rocks and minerals for testing and calibrating instruments to be flown in space missions. The characteristics of the analogue materials are documented in an accompanying online database. In view of the recent and upcoming rover missions to Mars (NASA’s 2011 Mars Science Laboratory (MSL) and ESA/Roscosmos’ 2018 ExoMars), we are concentrating initially on materials of direct relevance to the red planet. The initial collection consists of 15 well-studied rock and mineral samples, including a variety of basalts (ultramafic, weathered, silicified, primitive), sediments (volcanic sands, chert, and a banded iron formation –BIF-), and the phyllosilicate nontronite (a clay). All the samples were characterised petrographically, petrologically, and geochemically using the types of analyses likely to be performed during in-situ missions, in particular ExoMars : hand specimen description ; optical microscopy ; mineralogical analysis by XRD, Raman and IR spectrometry ; iron phase analysis by Mössbauer spectroscopy (MBS), elemental analysis by Energy-Dispersive X-ray spectroscopy (EDX), microprobe, Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Mass Spectrometry (ICP-MS) ; and reduced carbon analysis by Raman spectrometry.
Effect of grain size distribution on Raman analyses and the consequences for in situ planetary missions.J. Raman Spectrosc. 443 (6) 916–925
Raman spectroscopy can be used for analysing both mineral and organic phases, thus allowing characterisation of the microbial-scale geological context as well as the search for possible traces of life. This method is therefore very useful for in situ planetary exploration missions. Compared with the myriad of sample preparation techniques available in terrestrial laboratories, the possibilities for sample preparation during in situ missions on other planetary bodies are extremely limited and are generally restricted to abrasion of rock surfaces or crushing of the target samples. Whereas certain techniques need samples to be prepared in powder form, such as X-ray diffraction, this kind of preparation is not particularly suitable for optical microscopy and/or Raman spectroscopy. In this contribution, we examine the effects of powdering rock and mineral samples on optical observations and Raman analyses. We used a commercial Raman spectrometer, as well as a Raman laser spectrometer that simulates the instrument being developed for the future ExoMars 2018 mission. The commercial Raman spectrometer documents significant modifications to the spectra of the powdered samples, including broadening of the peaks and shifts in their position, as well as the appearance of new peaks. These effects are caused by localised heating of the sample under the laser beam and amplification of nominal surface effects due to the increase in surface area in finer grain sizes. However, most changes observed in the Raman spectra using the Raman laser spectrometer system are negligible because the relatively large (50 µm diameter) laser spot size produces lower irradiance. Furthermore, minor phases were more easily detectable in the powdered samples. Most importantly, however, this sample preparation method results in the loss of the textural features and context, making identification of potential fossilized microbial remains more problematic.
Ancient geological materials are likely to be contaminated through geological times. Thus, establishing the syngeneity of the organic matter embedded in a mineral matrix is a crucial step in the study of very ancient rocks. This is particularly the case for Archean siliceous sedimentary rocks (cherts), which record the earliest traces of life. We used electron paramagnetic resonance (EPR) for assessing the syngeneity of organic matter in cherts that have a metamorphic grade no higher than greenschist. A correlation between the age of Precambrian samples and the shape of their EPR signal was established and statistically tested. As thermal treatments impact organic matter maturity, the effect of temperature on this syngeneity proxy was studied ; cyanobacteria were submitted to cumulative short thermal treatment at high temperatures followed by an analysis of their EPR parameters. The resulting carbonaceous matter showed an evolution similar to that of a thermally treated young chert. Furthermore, the possible effect of metamorphism, which is a longer thermal event at lower temperatures, was ruled out for cherts older than 2 Gyr, based on the study of Silurian cherts of the same age and same precursors but various metamorphic grades. We determined that even the most metamorphosed sample did not exhibit the lineshape of an Archean sample. In the hope of detecting organic contamination in Archean cherts, a "contamination-like" mixture was prepared and studied by EPR. It resulted that the lineshape analysis alone does not allow contamination detection and that it must be performed along with cumulative thermal treatments. Such treatments were applied to three Archean chert samples, making dating of their carbonaceous matter possible. We concluded that EPR is a powerful tool to study primitive organic matter and could be used in further exobiology studies on low-metamorphic grade samples (from Mars for example).
Lanthanide-Based, Near-Infrared Luminescent and Magnetic Lipoparticles : Monitoring Particle IntegritySmall 9 (16) 2662-2666
Near-infrared emitting, magnetic particles for combined optical and MR detection based on liposomes or artificial lipoproteins are presented. They provide a novel strategy for the luminescence sensitization of lanthanide cations (Yb3+, Nd3+) without covalent bonds between the chromophore and the lanthanide, and provide an unambiguous tool for monitoring the integrity of the liponanoparticles, via emission in the NIR region.
Opaline silica was detected, with Raman spectroscopy, in carbonaceous microfossils (especially Myxococcoides) in silicified filamentous microbial mats within dolomitized conglomerates of the Draken Formation (- 800 to - 700 Ma). High-resolution electron microscopy (HRTEM) and microprobe analyses were used to confirm the nature of this phase in the quartz matrix of the microbial mats. The silica likely precipitated in a icrocrystalline form onto the organic macromolecules around, and within, the degrading microorganisms and preserved them by inhibiting the natural phase change to quartz. The Raman signal of opaline silica associated with carbonaceous matter and other iosignatures could be a potential indicator of biogenicity. This kind of association could be very useful during the future ExoMars mission (ESA/Roscosmos, 2018) that will earch for traces of past life on Mars.
Westall, F., Anbar, A., Fischer, W., Kump, L. (2012)
The great oxidation event : an expert discussion on the causes, the processes, and the still unknowns. Interview by Frances Westall.Astrobiology (2012à 12 (12) 1157-1162 - doi : 10.1089/ast.2012.1110 Bertrand J.C., Brochier C., Gouy M. and Westall F. (2012)
Cet ouvrage, co-écrit par Jean-Claude BERTRAND (Université de la Méditerranée, Marseille), Pierre CAUMETTE (Université de Pau), Philippe LEBARON (Université Pierre et Marie Curie, Banyuls/Mer), Robert MATHERON (Université Paul Cezanne , Marseille) et Philippe NORMAND (Université Claude Bernard, Lyon), est un traité d’écologie microbienne dont l’objectif est l’étude des micro-organismes dans les milieux naturels et anthropisés. Le « compartiment microbien », qui est une composante des écosystèmes, regroupe les procaryotes et eucaryotes unicellulaires ; les virus sont également objet d’étude dans la mesure où ils sont impliqués dans des problématiques écologiques et environnementales.
L’ouvrage, qui n’a pas d’équivalent en langue française, s’adresse prioritairement aux étudiants des licences et des masters scientifiques et professionnels, et aux doctorants. Il est également très utile aux chercheurs et aux enseignants-chercheurs, en particulier les microbiologistes et les écologues, qui souhaitent approfondir leur connaissance de la microbiologie des milieux naturels.
Preservation and evolution of organic matter during experimental fossilisation of the hyperthermophilic archaea Methanocaldococcus jannaschiiOrig Life Evol Biosph. 42 (6) 587-609
Identification of the earliest traces of life is made difficult by the scarcity of the preserved microbial remains and by the alteration and potential contamination of the organic matter (OM) content of rocks. These factors can confuse interpretations of the biogenicity and syngenicity of fossilised structures and organic molecules found in ancient rocks. In order to improve our knowledge of the fossilisation processes and their effects at the molecular level, we made a preliminary study of the fate of OM during experimental fossilisation. Changes in the composition and quantity of amino acids, monosaccharides and fatty acids were followed with HPLC, GC and GC-MS analyses during 1 year of silicification of the hyperthermophilic Archaea Methanocaldococcus jannaschii. Although the cells themselves did not fossilise and the accompanying extracellular polymeric substances (EPS) did, our analyses showed that the OM initially present in both cells and EPS was uniformly preserved in the precipitated silica, with amino acids and fatty acids being the best preserved compounds. This study thus completes previous data obtained by electron microscopy investigations of simulated microbial fossilisation and can help better identification and interpretation of microbial biosignatures in both ancient rocks and in recent hydrothermal formations and sediments.
Electron paramagnetic resonance study of a photosynthetic microbial mat and comparison with archean chertsOrig Life Evol Biosph. 42 (6) 569-585
Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.
Ironstones and iron-rich limestones regularly occur as components of time-specific intervals of the Palaeozoic as well as in younger times (Brett et al., this issue). Silurian sediments deposited at high latitudes along the peri-Gondwana border are characterized by black and white limestone and graptolitic shale sequences. Those in the Carnic Alps (southern Austria) additionally contain colourful pink to red limestones and ironstones. Laminated structures such as the (ferruginous)-coatings around skeletal fragments (mostly trilobites and some cephalopods and echinoderms) and stromatolitic features along discontinuity surfaces display dark red, green, white and brownish colours due to the presence of goethite,magnetite, hematite, chamosite, calcite and subordinate apatite.
Confocal laser Raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceousmatter associatedwith fossilizedmicrobial structures in the form of stromatolites, filaments and coccoids, suggesting a microbial role in the colouring of the Silurian world of the Carnic Alps. Iron concentrations up to 30× that of matrix and surrounding non-ferruginous rocks suggest blooms of iron microbe activity in response to the time-specific occurrence of chemically charged sea water during global biotic events.
Hydrous clay minerals detected on the surface of Mars have been interpreted as indicators of the hydrologic and climatic evolution of the planet. The iron- and magnesium-rich clays described in thick, extensive outcrops of Noachian crust have been proposed to originate from aqueous weathering. This would imply that liquid water was stable at the surface of early Mars, presumably when the climate was warmer and wetter. Here we show that iron- and magnesium-rich clays can alternatively form by direct precipitation from residual, water-rich magma-derived fluids. Infrared reflectance spectra from terrestrial lavas from the Mururoa Atoll (French Polynesia) that underwent this precipitation process are similar to those measured for the Noachian crust. Such an origin is also consistent with the D/H ratio of iron- and magnesium-rich clays in some martian meteorites and the widespread presence of these clays in massive basaltic lavas, breccias and regolith. We propose that the progressive degassing of the martian interior over time and the resultant increasingly water-poor magmatic fluids—and not a cooling climate—may explain the absence of clays in Hesperian-aged and more recent formations.
The PROCESS experiment : an astrochemistry laboratory for solid and gaseous organic samples in low Earth orbit.Astrobiology 12 (5) 412-425
The PROCESS (PRebiotic Organic ChEmistry on the Space Station) experiment was part of the EXPOSE-E payload outside the European Columbus module of the International Space Station from February 2008 to August 2009. During this interval, organic samples were exposed to space conditions to simulate their evolution in various astrophysical environments. The samples used represent organic species related to the evolution of organic matter on the small bodies of the Solar System (carbonaceous asteroids and comets), the photolysis of methane in the atmosphere of Titan, and the search for organic matter at the surface of Mars. This paper describes the hardware developed for this experiment as well as the results for the glycine solid-phase samples and the gas-phase samples that were used with regard to the atmosphere of Titan. Lessons learned from this experiment are also presented for future low-Earth orbit astrochemistry investigations.
The PROCESS Experiment : Exposure of amino acids in the EXPOSE-E experiment on the ISS and in laboratory simulations.Astrobiology 12 (5) 426-435
To understand the chemical behavior of organic molecules in the space environment, amino acids and a dipeptide in pure form and embedded in meteorite powder were exposed in the PROCESS experiment in the EXPOSE-E facility mounted on the European Technology Exposure Facility (EuTEF) platform on board the International Space Station (ISS). After exposure to space conditions for 18 months, the samples were returned to Earth and analyzed in the laboratory for reactions caused by solar UV and cosmic radiation. Chemical degradation and possible racemization and oligomerization, the main reactions caused by photochemistry in the vacuum ultraviolet domain (VUV, wavelength range 100–200 nm for photon energy from 6.2 to 12.4 eV) were examined in particular. The molecules were extracted and derivatized by silylation and analyzed by gas chromatograph coupled to a mass spectrometer (GC-MS) to quantify the rate of the degradation of the compounds. Laboratory exposure in several wavelength ranges from UV to VUV was carried out in parallel in the Cologne Deutsches Zentrum für Luft- und Raumfahrt (DLR) Center and Centre de biophysique moléculaire (CBM) laboratories. The results show that resistance to irradiation is a function of the chemical nature of the exposed molecules and the wavelengths of the UV light. The most altered compounds were the dipeptide, aspartic acid, and aminobutyric acid. The most resistant were alanine, valine, glycine, and aminoisobutyric acid. Our results also demonstrate the protective effect of meteorite powder, which reemphasizes the importance of exogenic contribution to the inventory of prebiotic organics on early Earth.
Analyses by the Mars Exploration Rover (MER), Spirit, of Martian basalts from Gusev crater show that they are chemically very different from terrestrial basalts, being characterized in particular by high Mg- and Fe-contents. To provide suitable analog basalts for the International Space Analogue Rockstore (ISAR), a collection of analog rocks and minerals for preparing in situ space missions, especially, the upcoming Mars mission MSL- 2011 and the future international Mars-2018 mission, it is necessary to synthesize Martian basalts. The aim of this study was therefore to synthesize Martian basalt analogs to the Gusev crater basalts, based on the geochemical data from the MER rover Spirit. We present the results of two experiments, one producing a quench-cooled basalt (<1 h) and one producing a more slowly cooled basalt (1 day). Pyroxene and olivine textures produced in the more slowly cooled basalt were surprisingly similar to spinifex textures in komatiites, a volcanic rock type very common on the early Earth. These kinds of ultramafic rocks and their associated alteration products may have important astrobiological implications when associated with aqueous environments. Such rocks could provide habitats for chemolithotrophic microorganisms, while the glass and phyllosilicate derivatives can fix organic compounds.
Brack, A. (2011)
Biological homochirality Comment on "Photochirogenesis : Photochemical models on the absolute asymmetric formation of amino acids in interstellar space" by Uwe J. Meierhenrich et alPhysics of Life Reviews (2011) 8 (3) 331-332 - doi : 10.1016/j.plrev.2011.08.008 Westall, F. ; Cavalazzi, B. ; Lemelle, L. ; Marrocchi, Y. ; Rouzaud, J.-N. ; Simionovici, A. ; Salomé, M. ; Mostefaoui, S. ; Andreazza, C. ; Foucher, F. ; Toporski, J. ; Jauss, A. ; Thiel, V. ; Southam, G. ; MacLean, L. ; Wirick, S. ; Hofmann, A. l. ; Meibom, A. ; Robert, F. and Défarge, C. (2011)
Implications of in situ calcification for photosynthesis in a 3.3 Ga-old microbial biofilm from the Barberton greenstone belt, South AfricaEarth and Planetary Science Letters 2011, 310, (3–4), 468-479
Timing the appearance of photosynthetic microorganisms is crucial to understanding the evolution of life on Earth. The ability of the biosphere to use sunlight as a source of energy (photoautotrophy) would have been essential for increasing biomass and for increasing the biogeochemical capacity of all prokaryotes across the range of redox reactions that support life. Typical proxies for photosynthesis in the rock record include features, such as a mat-like, laminated morphology (stratiform, domical, conical) often associated with bulk geochemical signatures, such as calcification, and a fractionated carbon isotope signature. However, to date, in situ, calcification related to photosynthesis has not been demonstrated in the oldest known microbial mats. We here use in situ nanometre-scale techniques to investigate the structural and compositional architecture in a 3.3 billion-year (Ga) old microbial biofilm from the Barberton greenstone belt, thus documenting in situ calcification that was most likely related to anoxygenic photosynthesis. The Josefsdal Chert Microbial Biofilm (JCMB) formed in a littoral (photic) environment. It is characterised by a distinct vertical structural and compositional organisation. The lower part is calcified in situ by aragonite, progressing upwards into uncalcified kerogen characterised by up to 1% sulphur, followed by an upper layer that contains intact filaments at the surface. Crystallites of pseudomorphed pyrite are also associated with the biofilm suggesting calcification related to the activity of heterotrophic sulphur reducing bacteria. In this anoxygenic, nutrient-limited environment, the carbon required by the sulphur reducing bacteria could only have been produced by photoautotrophy. We conclude that the Josfsdal Chert Microbial Biofilm was formed by a consortium of anoxygenic microorganisms, including photosynthesisers and sulphur reducing bacteria.
Prebiotic Significance of Extraterrestrial Ice Photochemistry : Detection of Hydantoin in Organic ResiduesAstrobiology 11 (9) 847-854
The delivery of extraterrestrial organic materials to primitive Earth from meteorites or micrometeorites has long been postulated to be one of the origins of the prebiotic molecules involved in the subsequent apparition of life. Here, we report on experiments in which vacuum UV photo-irradiation of interstellar/circumstellar ice analogues containing H(2)O, CH(3)OH, and NH(3) led to the production of several molecules of prebiotic interest. These were recovered at room temperature in the semi-refractory, water-soluble residues after evaporation of the ice. In particular, we detected small quantities of hydantoin (2,4-imidazolidinedione), a species suspected to play an important role in the formation of poly- and oligopeptides. In addition, hydantoin is known to form under extraterrestrial, abiotic conditions, since it has been detected, along with various other derivatives, in the soluble part of organic matter of primitive carbonaceous meteorites. This result, together with other related experiments reported recently, points to the potential importance of the photochemistry of interstellar "dirty" ices in the formation of organics in Solar System materials. Such molecules could then have been delivered to the surface of primitive Earth, as well as other telluric (exo-) planets, to help trigger first prebiotic reactions with the capacity to lead to some form of primitive biomolecular activity.
Potential Fossil Endoliths in Vesicular Pillow Basalt, Coral Patch Seamount, Eastern North Atlantic Ocean.Astrobiology 11 (7) 619-632
The chilled rinds of pillow basalt from the Ampere-Coral Patch Seamounts in the eastern North Atlantic were studied as a potential habitat of microbial life. A variety of putative biogenic structures, which include filamentous and spherical microfossil-like structures, were detected in K-phillipsite-filled amygdules within the chilled rinds. The filamentous structures (similar to 2.5 mu m in diameter) occur as K-phillipsite tubules surrounded by an Fe-oxyhydroxide (lepidocrocite) rich membranous structure, whereas the spherical structures (from 4 to 2 mu m in diameter) are associated with Ti oxide (anatase) and carbonaceous matter. Several lines of evidence indicate that the microfossil-like structures in the pillow basalt are the fossilized remains of microorganisms. Possible biosignatures include the carbonaceous nature of the spherical structures, their size distributions and morphology, the presence and distribution of native fluorescence, mineralogical and chemical composition, and environmental context. When taken together, the suite of possible biosignatures supports the hypothesis that the fossil-like structures are of biological origin. The vesicular microhabitat of the rock matrix is likely to have hosted a cryptoendolithic microbial community. This study documents a variety of evidence for past microbial life in a hitherto poorly investigated and underestimated microenvironment, as represented by the amygdules in the chilled pillow basalt rinds. This kind of endolithic volcanic habitat would have been common on the early rocky planets in our Solar System, such as Earth and Mars. This study provides a framework for evaluating traces of past life in vesicular pillow basalts, regardless of whether they occur on early Earth or Mars.
Metal cation binding by the hyperthermophilic microorganism, Archaea Methanocaldococcus Jannaschii, and its effects on silicification.Palaeontology 54 (5) 953-964 Orange, F. Chabin, A. Gorlas, A. Lucas-Staat, S. Geslin, C. Le Romancer, M. Prangishvili, D. Forterre, P. & Westall, F. (2011)
Volcaniclastic habitats for early life on Earth and Mars : A case study from ∼3.5 Ga-old rocks from the Pilbara, AustraliaPlanetary and Space Science 59 (10) 1093-1106 Westall, F. (2011)
Brack, A., Trouble, M. (2010)
Life is commonly referred as open systems driven by organic chemistry capable to self reproduce and to evolve. The notion of life has also been extended to non chemical systems such as robots. The key characteristics of living systems, i.e. autonomy, self-replication, self-reproduction, self-organization, self-aggregation, autocatalysis, as defined in chemistry and in robotics, are compared in a dialogue between a chemist and a robotitian.
Primitive life, defined as a chemical system capable to transfer its molecular information via self-replication and also capable to evolve, originated about 4 billion years ago from the processing of organic molecules by liquid water. Terrestrial atmosphere played a key role in the process by allowing the permanent presence of liquid water and by participating in the production of carbon-based molecules. Water molecules exhibit specific properties mainly due to a dense network of hydrogen bonds. The carbon-based molecules were either home made in the atmosphere and/or in submarine hydrothermal systems or delivered by meteorites and micrometeorites. The search for possible places beyond the earth where the trilogy atmosphere/water/life could exist is the main objective of astrobiology. Within the Solar System, exploration missions are dedicated to Mars, Europa, Titan and the icy bodies. The discovery of several hundreds of extrasolar planets opens the quest to the whole Milky Way.
The Mars Astrobiology Explorer-Cacher (MAX-C) : a potential rover mission for 2018. Final report of the Mars Mid-Range Rover Science Analysis Group (MRR-SAG)Astrobiology 10 (2) 127-163
This report documents the work of the Mid-Range Rover Science Analysis Group (MRR-SAG), which was assigned to formulate a concept for a potential rover mission that could be launched to Mars in 2018. Based on programmatic and engineering considerations as of April 2009, our deliberations assumed that the potential mission would use the Mars Science Laboratory (MSL) sky-crane landing system and include a single solar-powered rover. The mission would also have a targeting accuracy of approximately 7 km (semimajor axis landing ellipse), a mobility range of at least 10 km, and a lifetime on the martian surface of at least 1 Earth year. An additional key consideration, given recently declining budgets and cost growth issues with MSL, is that the proposed rover must have lower cost and cost risk than those of MSL—this is an essential consideration for the Mars Exploration Program Analysis Group (MEPAG). The MRR-SAG was asked to formulate a mission concept that would address two general objectives : (1) conduct high priority in situ science and (2) make concrete steps toward the potential return of samples to Earth. The proposed means of achieving these two goals while balancing the trade-offs between them are described here in detail. We propose the name Mars Astrobiology Explorer-Cacher(MAX-C) to reflect the dual purpose of this potential 2018 rover mission.
Micro-RAMAN Characterization of Precambrian Permineralized Cells, Draken Formation Preliminary Results.Origins of Life and Evolution of Biospheres - 40 (6) 528-529 Brack A. (2010)
Metals Binding by the Early Earth Analogue Microorganism, Archaea Methanocaldococcus jannaschu and its Effects on SilicificationOrigins of Life and Evolution of Biospheres - 40 (6) 526-527 Kminek, G. Rummel, J. D. Cockell, C. S. Atlas, R. Barlow, N. Beaty, D. Boynton, W. Carr, M. Clifford, S. Conley, C. A. Davila, A. F. Debus, A. Doran, P. Hecht, M. Heldmann, J. Helbert, J. Hipkin, V. Horneck, G. Kieft, T. L. Klingelhoefer, G. Meyer, M. Newsom, H. Ori, G. G. Parnell, J. Prieur, D. Raulin, F. Schulze-Makuch, D. Spry, J. A. Stabekis, P. E. Stackebrandt, E. Vago, J. Viso, M. Voytek, M. Wells, L. & Westall, F. (2010)
Testing the survival of microfossils in artificial martian sedimentary meteorites during entry into Earth’s atmosphere : the STONE 6 experiment.Icarus 207, 616-630
Brack, A. (2009)
Position paper : Science-Driven Scenario for Space Exploration from European Space Sciences Committee : ESSC.Astrobiology 9, 23-41. Westall, F., Lemelle, L., Simionovici, A., Salome, M., Marrocchi, Y., Foucher, F., Cavalazzi, B., Meibom, A., Robert, F., Mostafaoui, S., Jauss, A., Toporski, J., Laclean, L., Southam, G., Wirick, S., Villette, S., Jamme, F. & Dumas, P. (2009)
In situ analysis of the molecular organic and elemental composition of a 3.33 Ga microbial mat from Barberton.Geochim. Cosmochim. Acta 73, A1430. Westall, F. (2009)
Experimental Silicification of Thermophilic Microorganisms. Relevance for Early Life on Earth and Mars.Origins Life Evol. B. 39, 361-362. Orange, F., Westall, F., Disnar, J.R., Prieur, D., Bienvenu, N., Leromancer, M. & Defarge, C. (2009)
Experimental silicification of the extremophilic Archaea Pyrococcus abyssi and Methanocaldococcus jannaschii : applications in the search for evidence of life in early Earth and extraterrestrial rocks.Geobiology 7, 403-418. Foucher, F., Westall, F., Bény, J.M., Brandstätter, F. & Demets, R. (2009)
Walsh, M.M. and Westall, F. (2008)
Identification of morphological biosignatures in martian analogue field specimens using in situ planetary instrumentation.Astrobiology 8, 119-156. Westall, F (2008)
In situ imaging of organic sulfur in 700-800 My-old Neoproterozoic microfossils using X-ray spectromicroscopy at the SK-edgeOrganic Geochemistry 39 (2) 188-202
The study of very ancient microfossils has recently raised contentious issues regarding interpretation of the biogenicity of the structures. In situ investigation of certain elements such as sulfur within potential microfossils is a powerful complement to other methods of investigation that can provide valuable information on biogenicity. We present here a first such study on Precambrian microfossils from the 700-800-My-old Neoproterozoic Draken Formation, Svalbard, using scanning X-ray microscopy (SXM) in the fluorescence mode and X-ray absorption near edge spectroscopy (XANES) at the sulfur K-edge. SXM allowed mapping of up to 300 ppm of probably endogenous sulfur within the kerogenous walls of Myxococcoides chlorelloidea microfossils. XANES showed that the sulfur is most likely contained in heterocyclic organic compounds, such as thiophene(s). (C) 2007 Elsevier Ltd. All rights reserved.
Heterogeneous solid/gas organic compounds related to comets, meteorites, Titan and Mars : Laboratory and in lower Earth orbit experimentsAdvances in Space Research 42 (12) 2019-2035. Brandstätter, F ; Brack, A ; Baglioni, P ; Cockell, CS ; Demets, R ; Edwards, HGM ; Kurat, G ; Osinski, GR ; Pillinger, JM ; Roten, CA ; Sancisi- Frey, S (2008)
Separation of amino acid enantiomers via chiral derivatization and non chiral column by gas chromatographyJournal of Chromatography A 1180 (1-2), 131-137.
Two GC-MS methods for the enantioselective separation of the 20 proteinogenic amino acids are compared. Ethyl chloroformate and 2-chloropropanol were used to derivatize amino acid enantiomers. The diastereomers formed were separated on a non-chiral column by capillary gas chromatography. The separation performances were compared to those obtained when using non-chiral derivatization on a chiral column. (c) 2007 Elsevier B.V. All rights reserved.
Jakosky, B., Westall, F. and Brack, A. (2007)
The current approach to the study of the origin of life and to the search for life elsewhere is based on two assumptions. First, life is a purely physical phenomenon closely linked to specific environmental conditions. From this, we hypothesise that when these environmental conditions are met, life will arise and evolve. If these assumptions are valid, the search for life elsewhere should be a matter of mapping what we know about the range of environments in which life can exist, and then simply trying to find these environments elsewhere. Second, life can be clearly distinguished from the non-living world.
Morphological biosignatures from relict fossilised sedimentary geological specimens : a Raman spectroscopic studyJournal of Raman Spectroscopy 38 1352-1361
Morphological biosignatures (features related to life) and associated terrestrial sedimentary structures that provide possible sampling targets for the remote astrobiological exploration of planets have been analysed using Raman spectroscopic techniques. The spectral data from a suite of samples comprising cryptochasmoendoliths, preserved microbial filaments and relict sedimentary structures comprise a preliminary database for the establishment of key Raman biosignatures. This will form the basis for the evaluation of prototype miniaturised instrumentation for the proposed ESA ExoMars mission scheduled for 2013.
Identification of morphological biosignatures in martian analog field specimens using in situ planetary instrumentation : an integrated approachAstrobiology 8 119-156 Southam, G. & Westall, F. (2007)
The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for life but to aid the continual tectonic reworking and erosion that supply key redox contrasts and biochemical substrates to sustain habitability. Mud or soft sediment may be a biochemical prerequisite, to provide accessible substrate and protection. Once life begins, the habitat is widened by the activity of life, both by its management of the greenhouse and by partitioning reductants (e.g. dead organic matter) and oxidants (including waste products). Potential Martian habitats are discussed : by comparison with Earth there are many potential environmental settings on Mars in which life may once have occurred, or may even continue to exist. The long-term evolution of habitability in the Solar System is considered.
Nickel thin films deposited by sputtering methods on lithium fluoride single crystals have been strained to study the effect of the dislocation emergence on the mechanical behavior of coated materials. In these experiments, the samples had been investigated by in situ atomic force microscopy. It is shown that the buckling phenomenon preferentially occurs on the steps structures created by the dislocations coming from the substrate. In the frame of the Föppl-von Karman theory of thin plates, shape equations for the film on the area of emergence have been determined for the different levels of strain. These shape equations are compared to the experimental observations and it is concluded that the model needs to be modified to take into account the substrates effects.
Effect of the dislocation emergence on the mechanical behavior of coated materials : Elastic energy relaxation or adhesion modificationSource:Surface & Coatings Technology 202 (4-7) 1094-1097
Nickel thin films of various thicknesses deposited on lithium fluoride single crystals have been strained to study the effect of steps on the buckling phenomenon. In these experiments, the nanometer-scale steps result from the emergence process of dislocations coming from the substrate and piling-up at the film/substrate interface. The coated specimens were investigated by in situ atomic force microscopy. It is shown that the buckling phenomenon preferentially occurs just above the step structures in compression tests, while no buckling takes place in tension. From elastic energy consideration, it is concluded that the main effect of substrate plasticity is to strongly modify the critical stress for buckling, with no significant result on the adhesion properties. (c) 2007 Elsevier B.V. All rights reserved.
Interplanetary transfer of photosynthesis : An experimental demonstration of a selective dispersal filter in planetary island biogeographyAstrobiology 7 (1) 1-9
We launched a cryptoendolithic habitat, made of a gneissic impactite inoculated with Chroococcidiopsis sp., into Earth orbit. After orbiting the Earth for 16 days, the rock entered the Earth’s atmosphere and was recovered in Kazakhstan. The heat of entry ablated and heated the rock to a temperature well above the. upper temperature limit for life to below the depth at which light levels are insufficient for photosynthetic organisms (similar to 5 mm), thus killing all of its photosynthetic inhabitants.
Amino acids were most likely available on the primitive Earth, produced in the primitive atmosphere or in hydrothermal vents. Import of extraterrestrial amino acids may have represented the major supply, as suggested by micrometeorite collections and simulation experiments in space and in the laboratory. Selective condensation of amino acids in water has been achieved via N-carboxy anydrides. Homochiral peptides with an alternating sequence of hydrophobic and hydrophilic amino acids adopt stercoselective and thermostable beta-pleated sheet structures. Some of the homochiral beta-sheets strongly accelerate the hydrolysis of oligoribonucleotides. The beta-sheet-forming peptides have also been shown to protect their amino acids from racemization. Even if peptides are not able to self-replicate, i.e., to replicate a complete sequence from the mixture of amino acids, the accumulation of chemically active peptides on the primitive Earth appears plausible via thermostable and stercoselective beta-sheets made of alternating sequences.
Biologically uncommon D-aspartyl (D-Asp) residues have been detected in proteins of various tissues of elderly humans. The presence Of D-Asp has been explained as a result of the racemization of L-Asp (denoted as Asp) in the protein of inert tissues. We have previously suggested that the racemization of Asp may depend on the conformation of the peptide chain. However, the nature of the peptide conformation that affects the D-Asp formation has not yet been examined. Here we report the kinetics of Asp racemization in two model peptides, (Asp-Leu)(15) and (Leu-Asp-Asp-Leu)(8)-Asp, which form beta-sheet structures and ahelical structures, respectively.
Westall, F. and Southam, G. (2006)
A multidisciplinary study of silicified volcanoclastic, near-shore deposits from the 3.446 Ga "Kitty’s Gap Chert," Warrawoona. Group, Pilbara, reveals that they contain a wealth of carbonaceous microbial fossil remains. The volcanoclastic sediments host predominantly colonies of coccoidal microorganisms that occur in two modal size ranges, 0.4-0.5 mu m and 0.75-0.8 mu m. These microbial colonies coat the surfaces of the volcanic particles and form either dense, carpetlike associations up to tens of micrometers in diameter comprising hundreds of individuals. They also form less dense concentrations that include many chainlike associations of coccoids. All colonies are associated with a polymer film (extracellular polymeric substances-EPS) that coats both the organisms and their substrate. Multispecies biofllms formed at a boundary representing a short period of nondeposition. They consisted predominantly of coccoids and EPS but also included common, small filaments tens of micrometers in length and 0.25 mu m in width and rare, short rods 1 mu m in length. Carbon isotopic compositions of about -26 parts per thousand to -30 parts per thousand, measured on individual layers, are compatible with microbial fractionation. The biofilms include possible anoxygenic-photosynthesizing organisms (the filaments), whereas the colonies coating the volcanic clasts probably represent chemolithotrophic organisms. The interaction between the microbes, their colonies and biofilms, and their environment is intimate and complex. The environment provided the substrate and the nutrient, energy, and carbon sources, whereas the metabolic activity of the microbes contributed to the early diagenetic alteration of the volcanic particles, to the binding of the sediment, and to their silicification. The microorganisms were preserved by rapid silicification, with the silica coming partly from hydrothermal sources and partly from pore water enrichment in Si due to the devitrification of the volcanic protoliths (partially mediated by microbial activity).Our multidisciplinary approach to the study of this sample demonstrates the importance of using complementary methods in order to understand the complex microbe/sediment interactions and to be able to relate different types of microbial colonies/biofilms to different microenvironments. The observations and conclusions from this study have important consequences for the methods that need to be used in the search for traces of past life in general and especially in the search for past life on other planets such as Mars. They also form less dense concentrations that include many chainlike associations of coccoids. All colonies are associated with a polymer film (extracellular polymeric substances-EPS) that coats both the organisms and their substrate. Multispecies biofllms formed at a boundary representing a short period of nondeposition. They consisted predominantly of coccoids and EPS but also included common, small filaments tens of micrometers in length and 0.25 mu m in width and rare, short rods 1 mu m in length. Carbon isotopic compositions of about -26 parts per thousand to -30 parts per thousand, measured on individual layers, are compatible with microbial fractionation. The biofilms include possible anoxygenic-photosynthesizing organisms (the filaments), whereas the colonies coating the volcanic clasts probably represent chemolithotrophic organisms. The interaction between the microbes, their colonies and biofilms, and their environment is intimate and complex. The environment provided the substrate and the nutrient, energy, and carbon sources, whereas the metabolic activity of the microbes contributed to the early diagenetic alteration of the volcanic particles, to the binding of the sediment, and to their silicification. The microorganisms were preserved by rapid silicification, with the silica coming partly from hydrothermal sources and partly from pore water enrichment in Si due to the devitrification of the volcanic protoliths (partially mediated by microbial activity).
Four cherts sampled in the East Pilbara craton (Western Australia) at Marble Bar (Towers Formation), North Pole Dome (Dresser and Apex Basalt Formation), and Kittys Gap (Panorama Formation) were studied for micro- and nanomineralogy and geochemistry to determine their protoliths and to provide new insights on the physico-chemical and biological conditions of their depositional environments. The Marble Bar chert was formed at the interface with a basaltic rock. Hydrothermal fluids leached major and trace elements from the basalt and silicified the protolith of this chert. The elements Fe, Mn, Si, Ca, Mg, REE, An, Pd, Cr, and Ni precipitated as a microbanded iron formation (BIF) under reducing and alkaline conditions. The chert is composed of magnetite, carbonates, and quartz and forms a stromatolite-like structure. Later oxidizing fluids replaced magnetite and carbonates with Fe-Mn oxyhydroxides. They show vermicular microtextures and filamentous nanotextures. Each filament is composed of euhedral nanoscopic hematite. These oxides contain several thousands of ppm of N and C, and measured C/N ratios are similar to those observed in organic matter preserved in marine sediments, thus suggesting an organic activity.Two black cherts from hydrothermal dykes of the North Pole Dome are interpreted as having had a black shale precursor, based on the REE (rare earth elements) and trace metal characteristics. These rocks were probably entrained into the dykes and hydrothermally overprinted. Although these two cherts had the same history, the physico-chemical conditions differed during their formation. The chert from the chert-barite unit of the Dresser Formation was formed under reducing and alkaline conditions. This is clearly indicated by clusters of nanosulfide spherules replacing precursor minerals ; weblike Fe-sulfides intergrown with sphalerite ; As-pyrite and vaesite ; and the presence of carbonates. The black chert from the Apex Basalt Formation was formed under oxidizing conditions, as indicated by clusters of nanospherules of Fe-oxides and a negative Ce anomaly.A black and white laminated chert from Kittys Gap was formed in a shallow marine to subaerial environment, by silicification of a rhyodacitic volcaniclastic rock. This process was accompanied by the development of microbial mats on the sediment surfaces and the formation of microbial colonies around precursor K-feldspars, Ti-bearing biotites, amphiboles, and ghost spherulites. The environment was slightly oxidizing, as indicated by the negative Ce anomaly and the presence of Ti-oxides. The presence of K-bearing phyllosilicates rather than K-feldspars indicates that the environment was also slightly acidic. Elevated Cu and Zn contents in the black laminae point to a limited influence from hydrothermal fluids. The silica probably originated mainly from alteration of the minerals of the volcaniclastic rock due to diagenetic alteration by seawater. Two black cherts from hydrothermal dykes of the North Pole Dome are interpreted as having had a black shale precursor, based on the REE (rare earth elements) and trace metal characteristics. These rocks were probably entrained into the dykes and hydrothermally overprinted. Although these two cherts had the same history, the physico-chemical conditions differed during their formation. The chert from the chert-barite unit of the Dresser Formation was formed under reducing and alkaline conditions. This is clearly indicated by clusters of nanosulfide spherules replacing precursor minerals ; weblike Fe-sulfides intergrown with sphalerite ; As-pyrite and vaesite ; and the presence of carbonates. The black chert from the Apex Basalt Formation was formed under oxidizing conditions, as indicated by clusters of nanospherules of Fe-oxides and a negative Ce anomaly.
Implications of a 3.472-3.333 Gyr-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early EarthPhilosophical Transactions of The Royal Society B-Biological Sciences 361 (1474) 1857-1875
Modelling suggests that the UV radiation environment of the early Earth, with DNA weighted irradiances of about three orders of magnitude greater than those at present, was hostile to life forms at the surface, unless they lived in specific protected habitats. However, we present empirical evidence that challenges this commonly held view. We describe a well-developed microbial mat that formed on the surface of volcanic littoral sediments in an evaporitic environment in a 3.5-3.3 Ga-old formation from the Barberton greenstone belt. Using a multiscale, multidisciplinary approach designed to strongly test the biogenicity of potential microbial structures, we show that the mat was constructed under flowing water by 0.25 mu m filaments that produced copious quantities of extracellular polymeric substances, representing probably anoxygenic photosynthesizers.
We report experimental atomic force microscopy observations and analytical modeling of buckling structures of thin films deposited on single crystal substrates. The formation of straight-sided blisters just above the step structures resulting from the dislocations emergence has been observed and explained in the framework of the Foppl-von Karman theory of thin plates. A critical step height above which the buckling may occur has been determined and the asymmetry of the resulting blisters has been explained. Finally, the new buckling criterion has been compared with the classical one in the plane case and allows us to explain the blisters localization on step structures.
Westall, F (2005)
NRA analyses of N and C in hydromuscovite aggregates from a 3.5 Ga chert from Kittys Gap, Pilbara, AustraliaNuclear Instruments & Methods in Physics Research Section B-Beam Interactions With Materials and Atoms 231 536-540
Piophile elements nitrogen and carbon were found in hydromuscovite aggregates of an Archean chert from Kittys Gap, W. Australia, hosting probable evidence of life. Their concentrations do not show a linear relationship, as expected,if they where produced by a common organic source. The lack of a linear relationship is related to N and C fractionation at the mineral scale. N occurs in the form of NH4+, tightly retained at the K+ lattice sites, while C could occurs as a dispersed organic phase in hydromuscovite aggregates or in a weakly bounded form.. possibly HCO3-. (c) 2005 Elsevier B.V. All rights reserved.
The postbuckling transition from an initially straight-sided wrinkle to a distribution of bubbles has been investigated by means of finite element simulations in the case of a thin film relying on a rigid substrate. The calculations show that a snapthrough occurs when the buckling wavelength exceeds a critical value. Experimental atomic force microscopy observations of this transition have been reported and found to be in good agreement with the calculations. (c) 2005 American Institute of Physics.
Effect of substrate compliance on the global unilateral post-buckling of coatings : AFM observations and finite element calculationsActa Materialia 53 (2) 441-447
The post-critical regime of straight-sided wrinkles on compliant substrates of polycarbonate has been observed by atomic force microscope and investigated by means of finite element simulations. The effect of coupling between the film and its substrate has revealed a global buckling phenomenon, characterized by critical loads lower than those found in the case of a rigid substrate. Characteristic shapes of the buckled structure have been also found to spread over a region wider than the delaminated zone itself. A law relating the film deflexion to the stress has finally been established for any film/substrate system. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Collision-induced dissociation of peptide thioesters : the influence of peptide length on fragmentationEuropean Journal of Mass Spectrometry 11 31-34
Five peptide thioesters of increasing length were fragmented using two processes, in-source and in-collision cell fragmentation, using an electrospray source coupled to a triple quadrupole mass spectrometer. Comparison of their fragmentations was made in regard to their length. The two fragmentation conditions show that the peptide length has no influence on structural information and that the fragmentation efficiency is higher for the smallest peptides than for the longest. The particularity of these peptide thioesters consists of the neutral loss of ethanethiol. The absence of the a(3) fragment ion and the presence of the (a(3)-17) ion on the collision-induced dissociation mass spectra are noted.
Westall, F., Hofmann, B. & Brack, A. (2004)
Searching for fossil microbial biofilms on Mars : a case study using a 3.46 billion-year-old example from the Pilbara in Australia.ESA Spec. Pub. 545, 37-40 Hofmann, BA ; Westall, F ; Josset, JL ; Thomas, N ; Brack, A (2004)
Similar to 1.8 Ga iron-mineralized microblota from the Gunflint Iron Formation, Ontcario, Canada : implications for MarsAdvances in Space Research 33, 1268-1273
A similar to1.8 Ga banded-iron stromatolite from the Mink Mountain locality (PPRG 336) of the Gunflint Iron Formation, Ontario, Canada was investigated as an analogue to Martian hematite deposits which have the potential to contain fossilized Martian life. The stromatolitic sample was primarily composed of quartz (SiO2) with fractional amounts of hematite (Fe2O3), greenalite ((Fe,Mg)(3)Si2O5(OH)(2)), and minor amounts of stilpnomelane (K(Fe2+,Mg,Fe3+, Al)(8)(Si,Al)(12)(O,OH)(27) . 2H(2)O). Iron-bearing minerals were present within thin, discontinuous bands aligned roughly parallel. Octahedral pseudomorphs of hematite after magnetite occurred as localized elongate clusters, as well as on the outer rims of detrital oncolitic structures. Microcrystalline greenalite was present as a clay occurring in layers subparallel to the stromatolitic layering. Greenalite was observed in both the silica- and iron-rich layers, as well as within oncolitic structures. Irregular aggregates of radiating stilpnomelane needles extended into the silica matrix.
Meridiani Planum hematite deposit and the search for evidence of life on Mars - iron mineralization of microorganisms in rock varnishIcarus 171 (1) 20-30
The extensive hematite deposit in Meridiani Planum was selected as the landing site for the Mars Exploration Rover Opportunity because the site may have been favorable to the preservation of evidence of possible prebiotic or biotic processes. One of the proposed mechanisms for formation of this deposit involves Surface weathering and coatings, exemplified on Earth by rock varnish. Microbial life, including microcolonial fungi and bacteria, is documented in rock varnish matrices from the southwestern United States and Australia. Limited evidence of this life is preserved as cells and cell molds mineralized by iron oxides and hydroxides, as well as by manganese oxides. Such mineralization of microbial cells has previously been demonstrated experimentally and documented in banded iron formations, hot spring deposits, and ferricrete soils. These types of deposits are examples of the four "water-rock interaction" scenarios proposed for formation of the hematite deposit on Mars. The instrument suite on Opportunity has the capability to distinguish among these proposed formation scenarios and, possibly, to detect traces that are suggestive of preserved martian microbiota. However, the confirmation of microfossils or preserved biosignatures will likely require the return of samples to terrestrial laboratories. Published by Elsevier Inc.
The evidence for early life and its initial evolution on Earth is linked intimately with the geological evolution of the early Earth. The environment of the early Earth would be considered extreme by modem standards : hot (50-80degreesC), volcanically and hydrothermally active.. anoxic. high UV flux. and a high flux of extraterrestrial impacts. Habitats for life were more limited until continent-building processes resulted in the formation of stable cratons with wide, shallow, continental platforms in the Mid-Late Archaean. Unfortunately there are no records of the first appearance of life and the earliest isotopic indications of the existence of organisms fractionating carbon in similar to3.8 Ga rocks from the Isua greenstone belt in Greenland are tenuous. Well-preserved microfossils and microbial trials (in the form of tabular and domical stromatolites) occur in 3.5-3.3 Ga, Early Archaean, sedimentary formations from the Barberton (South Africa) and Pilbara (Australia) greenstone belts. They document life forms that show a relatively advanced level of evolution. Microfossil morphology includes filamentous, coccoid. rod and vibroid shapes. Colonial microorganisms formed biofilms and microbial mats at the surfaces of volcaniclastic and chemical sediments. some of which created (small) macroscopic microbialites such as stromatolites. Anoxygenic, photosynthesis may already have developed. Carbon. nitrogen and sulphur isotopes ratios are in the range of those for organisms with anaerobic metabolisms, such as methanogenesis, sulphate reduction and photosynthesis. Life was apparently distributed widely in shallow-water to littoral environments, including exposed, evaporitic basins and regions of hydrothermal activity. Biomass in the early Archaean was restricted owing to the limited amount of energy that could be produced by anaerobic metabolisms. Microfossils resembling oxygenic photosyrithesisers. such as cyanobacteria, probably first occurred in the later part of the Mid Archaean (similar to2.9 Ga), concurrent with the tectonic development of suitable shallow shelf environments. The development of an oxygenic metabolism allowed a considerable increase in biomass and increased interaction with the geological environment. Well-preserved microfossils and microbial trials (in the form of tabular and domical stromatolites) occur in 3.5-3.3 Ga, Early Archaean, sedimentary formations from the Barberton (South Africa) and Pilbara (Australia) greenstone belts. They document life forms that show a relatively advanced level of evolution. Microfossil morphology includes filamentous, coccoid. rod and vibroid shapes. Colonial microorganisms formed biofilms and microbial mats at the surfaces of volcaniclastic and chemical sediments. some of which created (small) macroscopic microbialites such as stromatolites. Anoxygenic, photosynthesis may already have developed. Carbon. nitrogen and sulphur isotopes ratios are in the range of those for organisms with anaerobic metabolisms, such as methanogenesis, sulphate reduction and photosynthesis. Life was apparently distributed widely in shallow-water to littoral environments, including exposed, evaporitic basins and regions of hydrothermal activity. Biomass in the early Archaean was restricted owing to the limited amount of energy that could be produced by anaerobic metabolisms. Microfossils resembling oxygenic photosyrithesisers. such as cyanobacteria, probably first occurred in the later part of the Mid Archaean (similar to2.9 Ga), concurrent with the tectonic development of suitable shallow shelf environments. The development of an oxygenic metabolism allowed a considerable increase in biomass and increased interaction with the geological environment.
Westall, F. & Drake, F. (2003)
Stephen Jay Gould (Full. House, Harmony Books, New York, 1996) emphasised the importance of the bacterial (prokaryote) world right from the beginnings of the history of life, up to the present day and, even into the future. Moreover, he suggested that the various forms of life on the planet today represent a diversification, or increase in complexity, from these simple organisms, rather than a directed evolution towards complexity. On the scale of evolution, the oldest fossils, dating back to almost 3.5 billion years ago, comprise simple unicellular organisms, i.e. prokaryotes that occur adjacent to the left wall of complexity. As far as can be ascertained from the fossil record, this early life had already exploited all the possible ramifications of diversification within an anaerobic environment and within the habitats available on the early Earth. Further evolution from this stage involved the development of organisms undertaking oxygenic photosynthesis that opportunistically invaded the newly formed, sunlight-bathed, shallow water continental platforms. (C) 2003 Academie des sciences. Publie par Editions scientifiques et medicales Elsevier SAS. Tous droits reserves.
New strategies for life detection and their implication for astrobiological research and Solar System explorationFrontiers of Life 267-271 - Editor(s) : Celnikier, LM ; Trân Than Vân, J Lenton, TM ; Caldeira, KG ; Franck, SA ; Horneck, G ; Jolly, A ; Rabbow, E ; Schellnhuber, HJ ; Száthmary, E ; Westall, F ; Zavarzin, GA ; Zimmermann-Timm, H (2003)
Exogenous carbonaceous microstructures in Early Archaean cherts and BIFs from the Isua Greenstone Belt : implications for the search for life in ancient rocksPrecambrian Research 126 (3-4) 313-330
The microstructure of HF-etched samples of Early Archaean banded iron formations (BIFs) and cherts from the >3.7 b.y.-old Isua Greenstone Belt (southwestern Greenland) was investigated using high resolution scanning electron microscopy equipped with an electron diffraction system, capable of analysing light elements. The rocks contain both endogenous (of internal origin) and exogenous (of external origin) carbonaceous microstructures. The former consist of inclusions of graphite and, possibly, small, amorphous carbonaceous particles, both embedded in metacherts (however, further in situ TEM studies are needed to verify the endogeneity of the amorphous particles). Moreover, these rocks also contain endolithic microorganisms (i.e. inhabiting cracks in rocks), as well as undifferentiated carbonaceous matter, that occur in fractures and cracks between grains.
1.8 Ga iron-mineralised microbiota from the Gunflint Iron Formation, Ontario, Canada : implications for MarsAdvances in Space Research 33-1268-1273 Brack, A (2003)
Gas chromatographic separation of saturated aliphatic hydrocarbon enantiomers on permethylated beta-cyclodextrinChirality 15 S13-S16 Suppl. S
Enantiomers of chiral aliphatic hydrocarbons are generally difficult to separate because they lack functional groups to be derivatized in order to generate diastereomers. The systematic and quantitative separation of a series of branched hydrocarbon enantiomers using a chiral cyclodextrin stationary phase and a cryostat-controlled gas chromatograph is described. The use of a cryogenic system allows the improvement of separations for various chiral aliphatic hydrocarbons. The molecular cyclodextrin-based mechanism of the achieved enantiomeric separations is discussed briefly. Possible applications of this analytical technique are summarized, with special emphasis on the planned enantiomeric separation experiment on a cometary nucleus. (C) 2003 Wiley-Liss, Inc.
Toporski, JKW ; Steele, A ; Westall, F ; Thomas-Keprta, KL ; McKay, DS (2002)
Winner of the 2001 Gerald A. Soffen Memorial Award - The simulated silicification of bacteria - New clues to the modes and timing of bacterial preservation and implications for the search for extraterrestrial microfossilsAstrobiology 2 (1) 1-26
Evidence of microbial, life on Earth has been found in siliceous rock formations throughout the geological and fossil record. To understand the mechanisms of silicification and thus improve our search patterns for evidence of fossil microbial life in rocks, a series of controlled laboratory experiments were designed to simulate the silicification of microorganisms. The bacterial strains Pseudomonas fluorescens and Desulphovibrio indonensis were exposed to silicifying media. The experiments were designed to determine how exposure time to silicifying solutions and to silicifying solutions of different Si concentration affect the fossilization of microbial biofilms. The silicified biofilms were analyzed using transmission electron microscopy (TEM) in combination with energy-dispersive spectroscopy. Both bacterial species showed evidence of silicification after 24 h in 1,000 ppm silica solution, although D. indonensis was less prone to silicification.
Morphologic and spectral investigation of exceptionally well-preserved bacterial biofilms from the Oligocene Enspel formation, GermanyGeochimica et Cosmochimica Acta 66 (10) 1773-1791
The fossilised soft tissues of a tadpole and an associated coprolitic structure from the organic-rich volcanoclastic lacustrine Upper Oligocene Enspel sediments (Germany) were investigated using high-resolution imaging techniques and nondestructive in situ surface analysis. Total organic carbon analysis of the coprolite and the sediment revealed values of 28.9 and 8.9% respectively. The soft tissues from the tadpole and the coprolite were found to be composed of 0.5 to 1 mum-sized spheres and rod shapes. These features are interpreted as the fossil remains of bacterial biofilms consisting probably of heterotrophic bacteria and fossilised extracellular polymeric substances.
Leucine, a-methyl leucine and two peptides were exposed to space conditions on board the MIR station during the Perseus-Exobiology mission. This long duration space mission was aimed at testing the delivery of prebiotic building blocks. During this mission, two amino acids (leucine and a-methyl leucine) and two peptides (leucine-diketopiperazine and trileucine thioethylester) were exposed in Earth orbit for three months. Basalt, clay and meteorite powder were also mixed with the samples in order to simulate the effects of potential meteorite protection.
Amino acids and amino acid derivatives were exposed to space conditions in Earth orbit as part of the ESA BIOPAN-2 mission to test the possible delivery of extraterrestrial biological building blocks to the primitive Earth. During the Biopan-2 mission, four proteinaceous amino acids (glycine, aspartic acid, glutamic acid and tyrosine), some amino acid esters and two peptides were exposed in Earth orbit for 10 days. Samples were exposed to vacuum and to solar radiation down to 120 nm both alone or associated with montmorillonite as dry films deposited on MgF2 windows. The compounds recovered after the flight were analysed in order to assess chemical degradation, racemization and polymerization.
Survival of microorganisms in space protected by meteorite material : Results of the experiment ’EXOBIOLOGIE’ of the PERSEUS missionAdvances in Space Research 30 (6) 1539-1545
During the early evolution of life on Earth, before the formation of a protective ozone layer in the atmosphere, high intensities of solar UV radiation of short wavelengths could reach the surface of the Earth. Today the full spectrum of solar UV radiation is only experienced in space, where other important space parameters influence survival and genetic stability additionly, like vacuum, cosmic radiation, temperature extremes, microgravity. To reach a better understanding of the processes leading to the origin, evolution and distribution of life we have performed space experiments with microorganisms. The ability of resistant life forms like bacterial spores to survive high doses of extraterrestrial solar UV alone or in combination with other space parameters, e.g. vacuum, was investigated.
Do meteoroids of sedimentary origin survive terrestrial atmospheric entry ? The ESA artificial meteorite experiment STONEPlanetary and Space Science 50 (7-8) 763-772
The 18 SNC meteorites identified to date are all igneous rocks, being basalts or basaltic cumulates. The lack of sedimentary rocks in this inventory is therefore surprising, in view of the collisional history of Mars and the likelihood that Mars experienced warmer conditions, possibly with a significant hydrosphere, earlier in its history. To address the possibility that sedimentary rocks ejected by impact from the surface of Mars may have reached the Earth, but did not survive terrestrial atmospheric entry, an experiment was performed in which samples of dolomite, a simulated Martian regolith (consisting of basalt fragments in a gypsum matrix) and a basalt were fixed to the heat shield of a recoverable capsule and flown in low Earth orbit. Temperatures attained during re-entry were high enough to melt basalt and the silica fibres of the heat shield and were therefore comparable to those experienced by meteorites.
Different mechanisms for the generation of circular polarization by the surface of planets and satellites are described. The observed values for Venus, the Moon, Mars, and Jupiter obtained by photo-polarimetric measurements with Earth based telescopes, showed accordance with theory. However, for planet Mercury asymmetric parameters in the circular polarization were measured that do not fit with calculations. For BepiColombo, the ESA cornerstone mission 5 to Mercury, we propose to investigate this phenomenon using a concept which includes two instruments. The first instrument is a high-resolution optical polarimeter, capable to determine and map the circular polarization by remote scanning of Mercury’s surface from the Mercury Planetary Orbiter MPO. The second instrument is an in situ sensor for the detection of the enantiomorphism of surface crystals and minerals, proposed to be included in the Mercury Lander MSE.
Amino acids are the essential molecular components of living organisms on Earth, but the proposed mechanisms for their spontaneous generation have been unable to account for their presence in Earth’s early history. The delivery of extraterrestrial organic compounds has been proposed as an alternative to generation on Earth, and some amino acids have been found in several meteorites. Here we report the detection of amino acids in the room-temperature residue of an interstellar ice analogue that was ultraviolet-irradiated in a high vacuum at 12 K. We identified 16 amino acids ; the chiral ones showed enantiomeric separation. Some of the identified amino acids are also found in meteorites. Our results demonstrate that the spontaneous generation of amino acids in the interstellar medium is possible, supporting the suggestion that prebiotic molecules could have been delivered to the early Earth by cometary dust, meteorites or interplanetary dust particles.
Leucine, alpha-methyl leucine and two peptides were exposed to space conditions on board the MIR station during the Perseus-Exobiology mission. This long duration space mission was aimed at testing the delivery of prebiotic building blocks. During this mission, two amino acids (leucine and alpha-methyl leucine) and two peptides (leucine-diketopiperazine and trileucine thioethylester) were exposed in Earth orbit for three months. Basalt, clay and meteorite powder were also mixed with the samples in order to simulate the effects of potential meteorite protection. Analysis of the material after the flight did not reveal any racemization or polymerisation but did provide information regarding photochemical pathways for the degradation of leucine and of the tripeptide.
Westall, F ; de Wit, MJ ; Dann, J ; van der Gaast, S ; de Ronde, CEJ ; Gerneke, D (2001)
Early Archean fossil bacteria and biofilms in hydrothermally-influenced sediments from the Barberton greenstone belt, South AfricaPrecambrian Research 106 (1-2) 93-116
SEM imaging of HF-etched, 3.3-3.5 Ga cherts from the Onverwacht Group, South Africa reveals small spherical (1 mum diameter) and rod-shaped structures (2-3.8 mum in length) which are interpreted as probable fossil coccoid and bacillar bacteria (prokaryotes), respectively, preserved by mineral replacement. Other, possibly biogenic structures include smaller rod-shaped bacteriomorphs (
The simulated silicification of bacteria - new clues to the modes and timing of bacterial preservation and implications for the search for extraterrestrial microfossilsAstrobiology 2 1-25 Gibson, EK ; McKay, DS ; Thomas-Keprta, KL ; Wentworth, SJ ; Westall, F ; Steele, A ; Romanek, CS ; Bell, MS ; Toporski, J (2001)
Analyses both support and are in opposition to the hypothesis that the Martian meteorite ALH84001 contains evidence for possible biogenic activity on Mars. New observations in two additional Martian meteorites, Nakhla (1.3 Ga old) and Shergotty (300-165 Ma old) indicate possible biogenic features. Features in the three Martian meteorites compare favorably with the accepted criteria for terrestrial microfossils and evidence for early life on the Earth. There is strong evidence for the presence of indigenous reduced carbon, biogenic magnetite, and the low-temperature formation of carbonate globules. The morphological similarities between terrestrial microfossils, biofilms, and the features found in the three Martian meteorites are intriguing but have not been conclusively proven. Every investigation must recognize the possibility of terrestrial contamination of the meteorites, whether or not the meteorites are Martian. The search for evidence of ancient life in Martian meteorites has emphasized the difficulties confronting the scientific community with the respect to the positive identification of evidence of past biogenic activity. (C) 2001 Elsevier Science B.V. All rights reserved.
Defining locations where conditions may have been favorable for life is a key objective for the exploration of Mars. Of prime importance are sites where conditions may have been favorable for the preservation of evidence of prebiotic or biotic processes. Areas displaying significant concentrations of the mineral hematite (a-Fe2O3), recently identified by thermal emission spectrometry, may have significance in the search for evidence of extraterrestrial life. Since iron oxides can form as aqueous mineral precipitates, the potential exists to preserve microscopic evidence of life in iron oxide-depositing ecosystems.
The question of the chemical origins of life is engraved in the European scientific patrimony as it can be traced back to the pioneer ideas of Charles Darwin, Louis Pasteur, and more recently to Alexander Oparin. During the last decades, the European community of origin of life scientists has organized seven out of the twelve International Conferences on the Origins of Life held since 1957. This community contributed also to enlarge the field of research to the study of life in extreme environments and to the search for extraterrestrial life, i.e. exobiology in its classical definition or astrobiology if one uses a more NASA-inspired terminology. The present paper aims to describe the European science background in exo/astrobiology as well as the project of a European Network of Exo/Astrobiology.
Gibson, EK ; McKay, DS ; Thomas-Keprta, K ; Westall, F ; Clemett, SJ (2000)
What is the status of the hypothesis of evidence of biogenic activity within martian meteorites : Alive or dead ?Meteoritics & Planetary Science 35 A60-A60 Suppl. S Westall, F ; Walsh, MM (2000)
Polymeric substances and biofilms as biomarkers in terrestrial materials : Implications for extraterrestrial samplesJournal of Geophysical Research-Planets 105 (E10) 24511-24527
Organic polymeric substances are a fundamental component of microbial biofilms. Microorganisms, especially bacteria, secrete extracellular polymeric substances (EPS) to form slime layers in which they reproduce. In the sedimentary environment, biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components. They are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps. Biofilms are almost ubiquitous wherever there is an interface and moisture (liquid/liquid, liquid/solid, liquid/gas, solid/gas). In sedimentary rocks they are commonly recognized as stromatolites.
Microscopic physical biomarkers in carbonate hot springs : Implications in the search for life on MarsIcarus 147 (1) 49-67
Physical evidence of life (physical biomarkers) from the deposits of carbonate hot springs were documented at the scale of microorganisms-submillimeter to submicrometer. The four moderate-temperature (57 to 72 degrees C), neutral pH springs reported on in this study, support diverse communities of bacteria adapted to specific physical and chemical conditions. Some of the microbes coexist with travertine deposits in endolithic communities. In other cases, the microbes are rapidly coated and destroyed by precipitates but leave distinctive mineral fabrics. Some microbes adapted to carbonate hot springs produce an extracellular polymeric substance which forms a three-dimensional matrix with living cells and cell remains, known as a biofilm.
Secondary minerals near and within fractures in Columbia River basalts contain objects the size and shape of bacteria. These bacteriomorphs are most commonly rods or ellipses but also include cocci and diplococci forms, vibrioids and club-shaped rods, and associated pairs of objects that suggest cellular division by binary fission. Secondary minerals associated with, enclosing, and making up bacteriomorphs include iron oxyhydroxides, sulfides, and smectites containing ferrous iron. The secondary minerals are intimately intermixed with kerogen. Moreover ; bacteriomorphs in the pyrite consist of kerogen. Careful consideration of mineral associations, the occurrence of organic carbon, and the spatial context of bacteriomorphs indicate that they are microfossils. The association of microfossils with minerals formed in reducing environments suggests an ancient ecosystem dominated at least. in part by sulfate-reducing bacteria, similar to communities within these basalts today.
Similarities in the early histories of Mars and Earth suggest the possibility that life may have arisen on Mars as it did on Earth. If this were the case, early deterioration of the environment on Mars (loss of surface water, decrease in temperature) may have inhibited further evolution of life. Thus, life on Mars would probably be similar to the simplest form of life on Earth, the prokaryotes. We present a hypothetical strategy to search for life on Mars consisting of (i) identifying a suitable landing site with good exobiological potential, and (ii) searching for morphological and biogeochemical signatures of extinct and extant life on the surface, in the regolith subsurface, and within rocks. The platform to be used in this theoretical exercise is an integrated, multi-user instrument package, distributed between a lander and rover, which will observe and analyse surface and subsurface samples to obtain the following information : 1. environmental data concerning the surface geology and mineralogy, UV radiation and oxidation processes ; 2. macroscopic to microscopic morphological evidence of life ; 3. biogeochemistry indicative of the presence of extinct or extant life ; 4. niches for extant life. Lastly, the rationale for human exploration of Mars will be addressed. (C) 2000 Elsevier Science Ltd. All rights reserved.
Delivery of extraterrestrial organics to the primitive Earth : UV-processing of amino acids in Earth orbitThe Role of Radiation in The Origin and Evolution of Life 87-96 - Editor(s) : Akaboshi, M ; Fujii, N ; Navarro-Gonzales, R ( Kyoto Univ. Press, Kyoto) Brack, A (2000)
Mineral surfaces probably participated in the chemical processes which led to life in the primitive oceans. The ordered conformations of simple acidic peptides exposed to insoluble minerals are described. Alternating poly(Glu-Leu) adopts a random coil conformation in water due to charge repulsion. The polypeptide extracts cations from insoluble crystalline CdS or molybdenum and adopts an ordered conformation. CdS leads to the formation of beta-sheets whereas molybdenum leads to alpha-helices, Peptides with at least 10-amino acids are necessary to exhibit a significative adsorption onto the surface, Under the same conditions, montmorillonite adsorbs the polypeptide but does not induce any conformational change.