We are studying cryptoendolith-bearing Antarctic sandstones, to determine if the microbes alter the elemental composition of the rocks. If there is an effect, then it might be a tracer for the presence of micro-organisms in martian surface materials

Blackhurst, R. L.

Grady, Monica

Jarvis, K.

Verchovsky, Sasha

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsCryptoendolith communities in Antarctic dry valleyregion sandstones: Potential analogues of Martianlife-formsConference or Workshop ItemHow to cite:Blackhurst, R. L.; Jarvis, K.; Verchovsky, Sasha and Grady, Monica (2003). Cryptoendolith communities inAntarctic dry valley region sandstones: Potential analogues of Martian life-forms. In: 34th Lunar and PlanetaryScience Conference, 17-21 Mar 2003, Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1576.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukCRYPTOENDOLITH COMMUNITIES IN ANTARCTIC DRY VALLEY REGION SANDSTONES:POTENTIAL ANALOGUES OF MARTIAN LIFE-FORMS.  Rebecca L. Blackhurst1, A. Verchovsky2, K. Jar-vis1 and M. M. Grady3, 1Dept. of Geological Sciences, Kingston University, Kingston, Surrey KT1 2EE, U.K.(K0019383@kingston.ac.uk), 2PSSRI, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K. 3Dept. ofMineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K. (mmg@nhm.ac.uk).Introduction:  Cryptoendolithic communitiescolonizing sandstones in the Dry Valleys of Antarcticahave been the subject of much research over recentyears, owing to their potential as analogues of Martianlife-forms. Interest in them stems from the similaritiesbetween the Antarctic cold desert ecosystems, repre-senting some of the most extreme of terrestrial envi-ronmental habitats, and the conditions pertaining at theMartian surface [1]. Cryptoendolithic microbial com-munities occur in the interstitial spaces of certaintranslucent sandstones [2, 3] and extend down to 10mmbelow the rock surface (Figure 1). They primarily con-sist of symbiotic or free living lichen and cyanobacteriaand their presence is identified by three coloured zonesin the profile of the substratum: 1) black pigmentedlichen; 2) white lichen, predominantly hyaline fungi;and, 3) microalgae (green algae and/or cyanobacteria)[4].Figure 1: Cryptoendolithic community in sand-stone from Battleship Promontory, Antarctica (sampleBP2). Field of view: 2cm.The stress tolerant nature of the microbes, particu-larly the cyanobacteria which possess a remarkablesuite of survival mechanisms, has resulted in the sug-gestion that they might be the type of micro-organismsthat could have flourished at the surface of an earlyMars. Previous studies have included Fourier Trans-form Raman spectroscopy in the near infrared(1064nm), to characterize a variety of key pigmentsand biomolecules produced by the communities. Ra-man spectroscopy has thus been identified as a usefultool that could be instrumental in detecting traces ofpast or present life in martian surface materials [1].It is clear from the distinct coloured biotic zonesthat the endolithic communities change their host rock.We are, therefore, investigating the possible effectthese microbes have on the chemistry of the sandstonesthey inhabit. Utilizing ICP-AES and ICP-MS tech-niques, we are undertaking a major, minor and traceelement study of the different layers within the sand-stones, to establish if, or how, these microbes influenceor directly affect the chemical composition of therocks. The chemical study is complemented by meas-urement of the abundance and stable isotopic composi-tion of carbon in the different layers. If elemental orisotopic variations are detected, then the nature andextent of these effects could add value to the potentialrole of cryptoendolithic communities as biomarkerswhen considering future in situ analysis of Martiansurface materials and Mars sample return rocks.Samples and Field Setting: The cryptoendolithichabitat is widespread throughout the Devonian quartz-ite sandstone of the Beacon Supergroup extendingfrom Victoria Land through the Transantarctic Moun-tains [4]. The rocky outcrops, snow cover and ambienttemperatures of ca –25o C characterize the Dry Valleyregions, with strong katabatic winds blowing off thePolar plateau; the relative humidity is 0% [5]. Severalsamples of cryptoendolithic communities were col-lected by a British Antarctic Survey expedition toTerra Nova Bay and the McMurdo Base during theAntarctic summer of 1995–1996 [5]. We have startedthe project by examining cryptoendolithic-bearingrocks collected from the Battleship Promontory (BP)region (76° 55'S 160° 55'E; altitude 1000m). They willbe compared with non-endolithic sandstones collectedfrom neighbouring regions.Sample Preparation and Analysis: A sample ofBP sandstone, designated BP2, was broken into twopieces. One was mounted and polished for optical andelectron microscope observations, whilst the second(Figure 1) was used for hand-picking grains forchemical and isotopic analysis.Mineralogy: Petrographic study of the samples in-dicated uniform examples of quartzite sandstones.They are fairly homogenous and predominantly quartzdominated (90%) with plagioclase feldspar (6%) andsome biotite mica (4%) identified. Samples in generalLunar and Planetary Science XXXIV (2003) 1576.pdfCRYPROENDOLITHS IN ANTARCTIC SANDSTONES:  R. L. Blackhurst et al.are moderately well sorted and range from fine tocoarse sand.Microscopy: Images and quantitative major andminor elemental analysis on carbon-coated probemounts were obtained using a Jeol 5900LV SEM oper-ating at 20kV and 1nA, with a working distance of10mm. Small pieces of each of the main samples wereselected and coated in Au/Pd for analysis with a Phil-lips XL30 SEM operating at 7kV with a working dis-tance of 10mm. The Phillips XL30 scanning electronmicroscope was used to detect and identify the mi-crobes in the samples. A thin white layer containinggrains coated by a black pigment could be seen in sam-ple BP2 with the naked eye (Figure 1). At magnifica-tions as low as x250, fungal hyphae were identified(Figure 2). Filamentous and non-filamentous microbesdensely populated this layer of the sample. The fila-mentous microbes clung to and in some cases com-pletely encased many of the quartz grains. There werealso non-filamentous microbes whose shapes, like flat-tened spheres, resembled blood cells. These were notas abundantly distributed throughout the layers as thefilamentous microbes.Figure 2: SEM image of filamentous microbes onquartz grains in BP2Carbon isotope analysis: was undertaken by highresolution stepped combustion-mass spectrometry,using the recently refurbished MS-86 static vacuumsystem at the Open University. The main sandstonematrix of BP2 was analysed, as were several blackgrains picked from the dark layer of BP2. The red-coloured main sandstone was, essentially, carbon free,containing < 0.1 wt. % organic carbon. In contrast, theblack grains consisted of ~ 15.2 wt. % carbon, withtotal δ13C of –27.6‰. All of the carbon in the samplewas organic in nature, and combusted below 400°C(Figure 3); there were no carbonates from terrestrialweathering, as is often the case in Antarctic rocks. Theorganic material was not a single component: the bi-modal nature of the release, with maxima in yield at275°C and 375°C, plus the variation in δ13C, indicatethe complex nature of the organics.Figure 3. Abundance (histogram, scaled on theLHS) and isotopic composition (circles, scaled on theRHS) of carbon released on combustion of 0.4 mg ofthe black layer from BP2. Errors in isotopic composi-tion are smaller than the size of the symbol.020040060080010001200-40-35-30-25-200 100 200 300 400 500Temperature (°C)[C]ppm/°Cδ13C(‰)Implications: Cryptoendolith communities haveemerged over the last few years as potentially impor-tant tracers for exobiological life detection. Similaritiesbetween the extremes of the Antarctic desert environ-ment and conditions on the Martian surface have sug-gested that cryptoendoliths might be suitable analoguesfor past or present life on Mars. Most approaches tothis comparison have characterized the biological sig-natures exhibited by the micro-organisms [e.g., 1].  Wehave started a search for elemental and isotopic effectsproduced by cryptoendoliths in a suite of quartzitesfrom the Dry Valley region of Antarctica. If our inves-tigation into the chemistry of the sandstones providesevidence that demonstrates a determinable influence bythe microbes on the rock chemistry, then the value ofthese communities as biomarkers will be enhanced.Hence, using the behaviour, characteristics and influ-ences of these terrestrial extremophiles, an importantastrobiological profile may be compiled to be used as aguide for future exobiological research.References: [1] Wynn-Williams D. D. and Edwards H. G.M. (2002) Icarus, 144, 486-503. [2] Friedmann E. I. (1982)Science, 215, 1045-1053. [3] Johnson C. G. and Vestal J. R.(1989) Geomicrobiol. J., 7, 137-153. [4] Russell N. C. et al.(1998) Antarctic Sci, 10, 63-74. [5] Edwards H. G. M. et al.(1997) J. Raman Spectrosc., 28, 685-690.Lunar and Planetary Science XXXIV (2003) 1576.pdf

Cryptoendolith communities in Antarctic dry valley region sandstones: Potential analogues of Martian life-forms

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Cryptoendolith communities in Antarctic dry valley region sandstones: Potential analogues of Martian life-forms

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