Fe-Rich Fossil Vents as Mars Analog Samples: Identification of Extinct Chimneys in Miocene Marine Sediments Using Raman Spectroscopy, X-Ray Diffraction, and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy.
Demaret, Lucas; Hutchinson, Ian B; Ingley, Richardet al.
Analog sample; Biosignatures; ExoMars; Hydrothermal; Iron crust; Mars 2020; Space and Planetary Science
Abstract :
[en] On Earth, the circulation of Fe-rich fluids in hydrothermal environments leads to characteristic iron mineral deposits, reflecting the pH and redox chemical conditions of the hydrothermal system, and is often associated with chemotroph microorganisms capable of deriving energy from chemical gradients. On Mars, iron-rich hydrothermal sites are considered to be potentially important astrobiological targets for searching evidence of life during exploration missions, such as the Mars 2020 and the ExoMars 2022 missions. In this study, an extinct hydrothermal chimney from the Jaroso hydrothermal system (SE Spain), considered an interesting geodynamic and mineralogical terrestrial analog for Mars, was analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The sample consists of a fossil vent in a Miocene shallow-marine sedimentary deposit composed of a marl substrate, an iron-rich chimney pipe, and a central space filled with backfilling deposits and vent condensates. The iron crust is particularly striking due to the combined presence of molecular and morphological indications of a microbial colonization, including mineral microstructures (e.g., stalks, filaments), iron oxyhydroxide phases (altered goethite, ferrihydrite), and organic signatures (carotenoids, organopolymers). The clear identification of pigments by resonance Raman spectroscopy and the preservation of organics in association with iron oxyhydroxides by Raman microimaging demonstrate that the iron crust was indeed colonized by microbial communities. These analyses confirm that Raman spectroscopy is a powerful tool for documenting the habitability of such historical hydrothermal environments. Finally, based on the results obtained, we propose that the ancient iron-rich hydrothermal pipes should be recognized as singular terrestrial Mars analog specimens to support the preparatory work for robotic in situ exploration missions to Mars, as well as during the subsequent interpretation of data returned by those missions.
Eppe, Gauthier ; Université de Liège - ULiège > Molecular Systems (MolSys)
Malherbe, Cédric ; Université de Liège - ULiège > Molecular Systems (MolSys) ; Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom
Language :
English
Title :
Fe-Rich Fossil Vents as Mars Analog Samples: Identification of Extinct Chimneys in Miocene Marine Sediments Using Raman Spectroscopy, X-Ray Diffraction, and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy.
Abbey WJ, Bhartia R, Beegle LW, et al. (2017) Deep UV Raman spectroscopy for planetary exploration: The search for in situ organics. Icarus 290:201-214.
Banfield JF, Moreau JW, Chan CS, et al. (2001) Mineralogical biosignatures and the search for life on Mars. Astrobiology 1: 447-465.
Baskar S, Baskar R, Thorseth IH, et al. (2012) Microbially induced iron precipitation associated with a neutrophilic spring at Borra Caves, Vishakhapatnam, India. Astrobiology 12:327-346.
Beegle L, Bhartia R, White M, et al. (2015) SHERLOC: scanning habitable environments with Raman and luminescence for organics and chemicals. In IEEE Aerospace Conference. IEEE, Piscataway, NJ.
Bibring J-P, Langevin Y, Mustard JF, et al. (2006) Global mineralogical and aqueous Mars history derived from OMEGA/ Mars Express data. Science 312, 400-404.
Bibring J-P, Hamm V, Pilorget C, et al. (2017) The MicrOmega investigation onboard ExoMars. Astrobiology 17:621-626.
Bishop JL, Murad E, Lane MD, et al. (2004) Multiple techniques for mineral identification on Mars: A study of hydrothermal rocks as potential analogues for astrobiology sites on Mars. Icarus 169:311-323.
Bost N, Westall F, Ramboz C, et al. (2013) Missions to Mars: characterisation of Mars analogue rocks for the International Space Analogue Rockstore (ISAR). Planet Space Sci 82-83: 113-127.
Böttger U, de Vera JP, Fritz J, et al. (2012) Optimizing the detection of carotene in cyanobacteria in a Martian regolith analogue with a Raman spectrometer for the ExoMars mission. Planet Space Sci 60:356-362.
Breier JA, White SN, and German CR (2010) Mineral-microbe interactions in deep-sea hydrothermal systems: A challenge for Raman spectroscopy. Philos Trans R Soc A Math Phys Eng Sci 368:3067-3086.
Brocks JJ, Love GD, Summons RE, et al. (2005) Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea. Nature 437:866-870.
Cady SL, Farmer JD, Grotzinger JP, et al. (2003) Morphological biosignatures and the search for life on Mars. Astrobiology 3:351-368.
Canet C and Prol-Ledesma RM (2007) Mineralizing processes at shallow submarine hydrothermal vents: examples from México. In Geology of México: Celebrating the Centenary of the Geological Society of México, edited by SA Alaniz-A lvarez and AF Nieto-Samaniego. Geological Society of America Spec. Papers, Colorado, p 422.
Chamley H (1989) Clay Sedimentology. Springer, Berlin, p 623.
Chan CS, De Stasio G, Welch SA, et al. (2004) Microbial polysaccharides template assembly of nanocrystal fibers. Science 303:1656-1658.
Chan CS, Fakra SC, Edwards DC, et al. (2009) Iron oxyhydroxide mineralization on microbial extracellular polysaccharides. Geochim Cosmochim Acta 73:3807-3818.
Chan CS, Fakra SC, Emerson D, et al. (2011) Lithotrophic ironoxidizing bacteria produce organic stalks to control iron mineral growth: implications for biosignature formation. ISME J 5:717-727.
Chan C, Emerson D, and Luther GW (2016a) The role of microaerophilic Fe-oxidizing microorganisms in producing banded iron formations. Geobiology 14:509-528.
Chan C, McAllister S, Leavitt A, et al. (2016b) The architecture of iron microbial mats reflects the adaptation of chemolithotrophic iron oxidation in freshwater and marine environments. Front Microbiol 7:796.
Chatzitheodoridis E, Haigh S, and Lyon I (2014) A conspicuous clay ovoid in Nakhla: evidence for subsurface hydrothermal alteration on Mars with implications for astrobiology. Astrobiology 14:651-693.
Chi Fru E, Ivarsson M, Kilias SP, et al. (2013) Fossilized iron bacteria reveal a pathway to the bio logical origin of banded iron formation. Nat Commun 4:1-7.
Chi Fru E, Ivarsson M, Kilias SP, et al. (2015) Biogenicity of an early quaternary iron formation, Milos Island, Greece. Geobiology 13:225-244.
Cornell RM and Schwertmann U (1996) The Iron Oxides: Structure, Properties, Reactions, Occurrence and Uses, VCH, Weinheim.
Czamara K, Majzner K, Pilarczyk M, et al. (2015) Raman spectroscopy of lipids: A review. J Raman Spectrosc 46:4-20.
de Faria DLA and Lopes FN (2007) Heated goethite and natural hematite: can Raman spectroscopy be used to differentiate them? Vib Spectrosc 45:117-1.
de Faria DLA, Silva SV, and de Oliveira MT (1997) Raman microspectroscopy of some iron oxides and oxy-hydroxides. J Raman Spectrosc 28:873-878.
Demaret L, Hutchinson IB, Eppe G, et al. (2020) Analytical strategy for representative subsampling of Raman-based robotic planetary exploration missions: The case study of solid dispersions of b-carotene and L-cysteine in gypsum. J Raman Spectrosc 51:1624-1635.
Di Bella MG, Sabatino S, Quartieri A, et al. (2019) Modern iron ooids of hydrothermal origin as a proxy for ancient deposits. Sci Rep 9, 7107.
Dodd MS, Papineau D, Grenne T, et al. (2017) Evidence for early life in Earth's oldest hydrothermal vent precipitates. Nature 543:60-64.
Edwards HG, Hutchinson I, and Ingley R (2012) The ExoMars Raman spectrometer and the identification of biogeological spectroscopic signatures using a flight-like prototype. Anal Bioanal Chem 404:1723-1731.
Emerson D (2012) Biogeochemistry and microbiology of microaerobic Fe(II) oxidation. Biochem Soc Trans 40:1211-1216.
Erfurt P (2021) The Geochemistry of Hot Springs. In The Geoheritage of Hot Springs. Geoheritage, Geoparks and Geotourism (Conservation and Management Series), edited by W. Eder, P.T. Bobrowsky, and J. Martínez-Frías. Springer, Cham, pp 51-90.
Farmer JD (1996) Hydrothermal systems on Mars: An assessment of present evidence. In Evolution of Hydrothermal Ecosystems on Earth (and Mars?), Ciba Foundation Symposium 202, edited by GR Bock and JA Goode. John Wiley and Sons, Chichester, United Kingdom, pp 273-299.
Farmer JD (2000) Hydrothermal systems: doorways to early biosphere evolution. GSA Today 10:1-9.
Ferris CG (2005) Biogeochemical properties of bacteriogenic iron oxides. Geomicrobiol J 22:79-85.
Floyd MAM, Williams AJ, Grubisic A, et al. (2018) Metabolic processes preserved as biosignatures in iron-oxidizing microorganisms: implications for biosignature detection on Mars. Astrobiology 19:40-52.
Fortin D and Langley S (2005) Formation and occurrence of biogenic iron-rich minerals. Earth Sci Rev 72:1-19.
Foucher F, Lopez-Reyes G, Bost N, et al. (2013) Effect of grain size distribution on Raman analyses and the consequences for in situ planetary missions. J Raman Spectrosc 44:916-925.
García-Ruiz JM, Carnerup A, Christy AG, et al. (2002) Morphology: An ambiguous indicator of biogenicity. Astrobiology 2:353-369.
Gasharova B, Mihailova B, and Konstantinov L (1997) Raman spectra of various types of tourmalines. Eur J Mineral 9:935-940.
Georgieva MN, Little CTS, Maslennikov VV, et al. (2021) The history of life at hydrothermal vents. Earth Sci Rev 217, 103602.
Gialanella S, Girardi F, Ischia G, et al. (2010) On the goethite to hematite phase transformation. J Therm Anal Calorim 102: 867-873.
Goesmann F, Brinckerhoff WB, Raulin F, et al. (2017) The Mars Organic Molecule Analyzer (MOMA) instrument: characterization of organic material in martian sediments. Astrobiology 17:655-685.
Goudge TA, Mustard JF, Head JW, et al. (2015) Assessing the mineralogy of the watershed and fan deposits of the Jezero crater paleolake system, Mars. J Geophys Res Planets 120: 775-808.
Hanert HH (2006) The genus Siderocapsa (and other iron-And manganese-oxidizing Eubacteria). In The Prokaryotes: Vol. 7: Proteobacteria: Delta, Epsilon Subclass, 3rd ed, edited by M Dworkin, S Falkow, E Rosenberg, K-H Schleifer, and E Stackebrandt. Springer, New York, pp 1005-1015.
Hanesch M (2009) Raman spectroscopy of iron oxides and (oxy)hydroxides at low laser power and possible applications in environmental magnetic studies. Geophys J Int 177:941-948.
Hays LE, Graham HV, Des Marais DJ, et al. (2017) Biosignature preservation and detection in Mars analog environments. Astrobiology 17:363-400.
Hirschberg J and Chamovitz D (1994) Carotenoids in Cyanobacteria. In The Molecular Biology of Cyanobacteria, edited by DA Bryant. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 559-579.
Hutchinson IB, Ingley R, Edwards HGM, et al. (2014) Raman spectroscopy on Mars: identification of geological and biogeological signatures in Martian analogues using miniaturized Raman spectrometers. Philos Trans R Soc A Math Phys Eng Sci 372:20140204.
Ivarsson M, Lausmaa J, Lindblom S, et al. (2008) Fossilized microorganisms from the Emperor Seamounts: implications for the search for a subsurface fossil record on Earth and Mars. Astrobiology 8:1139-1157.
Javaux EJ (2019) Challenges in evidencing the earliest traces of life. Nature 572:451-460.
Jehlicka J, Edwards HGM, and Oren A (2014) Raman spectroscopy of microbial pigments. Appl Environ Microbiol 80: 3286-3295.
Jiao Y, Kappler A, Croal LR, et al. (2005) Isolation and characterisation of a genetically tractable photoautotrophic Fe(II)-oxidizing bacterium, Rhodopseudomonas palustris strain TIE-1. Appl Environ Microbiol 71:4487-4496.
Juniper SK and Fouquet Y (1988) Filamentous iron-silica deposits from modern and ancient hydrothermal sites. Can Miner 26:859-869.
Kappler A, Pasquero C, Konhauser KO, et al. (2005) Deposition of banded iron formations by anoxygenic phototrophic Fe(II)-oxidizing bacteria. Geology 33:865-868.
Kendall B, Anbar AD, Kappler A, et al. (2012) The global iron cycle. In Fundamentals of Geomicrobiology, edited by AH Knoll, DE Canfield, and KO Konhauser. Wiley-Blackwell, New York, pp 65-92.
Kennedy CB, Scott SD, and Ferris FG (2003) Characterization of bacteriogenic iron oxide deposits from Axial Volcano, Juan de Fuca Ridge, Northeast Pacific Ocean. Geomicrobiol J 20:199-214.
Kennedy CB, Scott SD, and Ferris FG (2004) Hydrothermal phase stabilization of 2-line ferrihydrite by bacteria. Chem Geol 212:269-277.
Konhauser KO, Hamade T, Raiswell R, et al. (2002) Could bacteria have formed the Precambrian banded iron formations? Geology 30:1079-1082.
Laetsch T and Downs R (2006) Software for Identification and Comparison of Mineral Raman Data Using the RRUFF Project, RRUFF Project. Department of Geosciences, University of Arizona, Tucson.
Lalla E, Sanz-Arranz A, Lopez-Reyes G, et al. (2019) A micro-Raman and X-ray study of erupted submarine pyroclasts from El Hierro (Spain) and its' astrobiological implications. Life Sci Space Res (Amst) 21:49-64.
Langley S, Igric P, Takahashi Y, et al. (2009) Preliminary characterization and biological reduction of putative biogenic iron oxides (BIOS) from the Tonga-Kermadec Arc, southwest Pacific Ocean. Geobiology 7:35-49.
Laufer K, Nordhoff M, Halama M, et al. (2017) Microaerophilic Fe(II)-oxidizing Zetaproteobacteria isolated from low-Fe marine coastal sediments-physiology and characterization of their twisted stalks. Appl Environ Microbiol 83:e03118-16.
Little CTS, Glynn SEJ, and Mills RA (2004) Four-hundred andninety-million-year record of bacteriogenic iron oxide precipitation at sea-floor hydrothermal vents. Geomicrobiol J 21: 415-429.
Little CTS, Johannessen KC, Bengtson S, et al. (2021) A late Paleoproterozoic (1.74 Ga) deep-sea, low-Temperature, ironoxidizing microbial hydrothermal vent community from Arizona, USA. Geobiology 19:228-249.
Lopez-Reyes G, Rull F, Venegas G, et al. (2013) Analysis of the scientific capabilities of the ExoMars Raman Laser Spectrometer instrument. Eur J Miner 25:721-733.
Malherbe C, Ingley R, Hutchinson I, et al. (2015) Biogeological analysis of desert varnish using portable Raman spectrometers. Astrobiology 15:442-452.
Marshall CP, Dufresne WJB, and Rufledt CJ (2020) Polarized Raman spectra of hematite and assignment of external modes. J Raman Spectrosc 51:1522-1529.
Martin W, Baross J, Kelley D, et al. (2008) Hydrothermal vents and the origin of life. Nat Rev Microbiol 6:806-814.
Martinez-Frías J (1998) An Ancient Ba-Sb-Ag-Fe-Hg-bearing hydrothermal system in SE Spain. Episodes 21:248-252.
Martinez-Frías J, García Guinea J, López Ruiz J, et al. (1992) Discovery of fossil fumaroles in Spain. Econ Geol 87:444-447.
Martinez-Frías J, Lunar R, Rodriguez-Losada JA, et al. (2004) The volcanism related multistage hydrothermal system of El Jaroso (SE Spain): implications for the exploration of Mars. Earth Planet Space 56:5-8.
Martinez-Frías J, Amaral G, and Vázquez L (2006) Astrobiological significance of minerals on Mars surface environment. Rev Environ Sci Biotechnol 4:219-231.
Martinez-Frías J, Delgado-Huertas A, Garcia-Moreno F, et al. (2007) Isotopic signatures of extinct low-Temperature hydrothermal chimneys in the Jaroso Mars analog. Planet Space Sci 55:441-448.
Martins Z, Cottin H, Kotler JM, et al. (2017) Earth as a tool for astrobiology-A European perspective. Space Sci Rev 209: 43-81.
Mather A, Martín J M, Harvey AM, et al. (2001) A Field Guide to the Neogene Sedimentary Basins of the Almería Province, SE Spain. Blackwell Science, Oxford.
McMahon S (2019) Earth's earliest and deepest purported fossils may be iron-mineralized chemical gardens. Proc R Soc B Biol Sci 286:20192410.
Melton ED, Swanner ED, Behrens S, et al. (2014) The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle. Nat Rev Microbiol 12:797-808.
Miot J, Benzerara K, Obst M, et al. (2009) Extracellular iron biomineralization by photoautotrophic iron-oxidizing bacteria. Appl Environ Microbiol 75:5586-5591.
Moore DM and Reynolds RC, Jr. (1997) Identification of clay minerals and associated minerals. In X-ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford University Press, New York, pp 203-240.
Mustard JF, Adler M, Allwood A, et al. (2013) Report of the Mars 2020 science definition team. Mars Explor Progr Anal Gr 155-205.
Navarro A and Cardellach E (2008) Mobilization of Ag, heavy metals and Eu from the waste deposit of Las Herrerías mine (Almería, SE Spain). Environ Geol 56:1389-1401.
Ojha L, Karunatillake S, Karimi S, et al. (2021) Amagmatic hydrothermal systems on Mars from radiogenic heat. Nat Commun 12:1754.
Parenteau MN and Cady SL (2010) Microbial biosignatures in iron-mineralized phototrophic mats at Chocolate Pots Hot Springs, Yellowstone National Park, United States. Palaios 25:97-11.
Parenteau MN, Jahnke LL, Farmer JD, et al. (2014) Production and early preservation of lipid biomarkers in iron hot springs. Astrobiology 14:502-521.
Parnell J, Cullen D, Sims MR, et al. (2007) Searching for life on Mars: selection of molecular targets for ESA's Aurora Exo-Mars mission. Astrobiology 7:578-604.
Pierson BK and Parenteau MN (2000) Phototrophs in high iron microbial mats: microstructure of mats in iron-depositing hot springs. FEMS Microbiol Ecol 32:181-196.
Pirajno F and van Kranendonk MJ (2005) Review of hydrothermal processes and systems on Earth and implications for martian analogues. Aust J Earth Sci 52:329-351.
Posth NR, Canfield DE, and Kappler A (2014) Biogenic Fe (III) minerals: from formation to diagenesis and preservation in the rock record. Earth Sci Rev 135:103-121.
Potter-McIntyre SL, Chan MA, and McPherson BJ (2014) Textural and mineralogical characteristics of microbial fossils associated with modern and ancient iron (oxyhydr)oxides: Terrestrial analogue for sediments in Gale Crater. Astrobiology 14:1-14.
Preston L and Dartnell L (2014) Planetary habitability: lessons learned from terrestrial analogues. Int J Astrobiol 13: 81-98.
Prieto AC, Dubessy J, and Cathelineau M (1991) Structure-composition relationships in trioctahedral chlorites: A vibrational spectroscopy study. Clays Clay Miner 39:531-539.
Prieto-Ballesteros O, Martínez-Frías J, Schutt J, et al. (2008) The subsurface geology of Río Tinto: material examined during a simulated Mars drilling mission for the Mars Astrobiology Research and Technology Experiment (MARTE). Astrobiology 8:1013-1021.
Quantin-Nataf C, Carter J, Mandon L, et al. (2021) Oxia Planum: The landing site for the ExoMars ''Rosalind Franklin'' Rover mission: geological context and prelanding interpretation. Astrobiology 21:345-366.
Ramkissoon NK, Turner SMR, Macey MC, et al. (2021) Exploring the environments of martian impact-generated hydrothermal systems and their potential to support life. Meteoritic Planet Sci 56:1350-1368.
Romero-Viana L, Keely BJ, Camacho A, et al. (2010) Primary production in Lake La Cruz (Spain) over the last four centuries: based on sedimentary signal of photosynthetic pigments. J Paleolimnol 43:771-786.
Ruff SW, Farmer JD, Calvin WM, et al. (2011) Characteristics, distribution, origin, and significance of opaline silica observed by the Spirit rover in Gusev Crater, Mars. J Geophys Res 116, doi:10.1029/2010JE003767.
Ruff SW, Campbell KA, Van Kranendonk MJ, et al. (2020) The case for ancient hot springs in Gusev crater, Mars. Astrobiology 20:475-499.
Rull F, Maurice S, Hutchinson I, et al. (2017) The Raman laser spectrometer for the ExoMars rover mission to Mars. Astrobiology 17:627-654.
Schulze-Makuch D, Dohm JM, Fan C, et al. (2007) Exploration of hydrothermal targets on Mars. Icarus 189:308-324.
Simoneit BRT (2002) Molecular indicators (biomarkers) of past life. Anat Rec 268:186-195.
Steenberger CLM and Korthals HJ (1982) Distribution of photosynthetic microorganisms in the anaerobic and microaerophilic strata of Lake Vechten (The Netherlands). Pigment analysis and role in primary production. Limnol Oceanogr 27: 883-895.
Straub KL, Rainey FA, and Widdel F (1999) Rhodovulum iodosum sp. nov. and Rhodovulum robiginosum sp. nov., two new marine phototrophic ferrous-iron-oxidizing purple bacteria. Int J Syst Bacteriol 49:729-735.
Tan J and Sephton MA (2020) Organic records of early life on Mars: The role of iron, burial, and kinetics on preservation. Astrobiology 20:53-72.
Thibeau RJ, Brown CW, and Heidersbach RH (1978) Raman spectra of possible corrosion products of iron. Appl Spectrosc 32:532-535.
Toner BM, Berquó TS, Michel FM, et al. (2012) Mineralogy of iron microbial mats from Loihi Seamount. Front Microbiol 3: 118.
Vago JL, Westall F, Pasteur Teams, et al. (2017) Habitability on early Mars and the search for biosignatures with the ExoMars Rover. Astrobiology 17:471-510.
Vago JL, Westall F, Cavalazzi B, et al. (2018) Searching for signs of life on other planets: Mars a case study. In Biosignatures for Astrobiology, edited by B. Cavalazzi and F. Westall. Springer, Cham, Switzerland, pp 283-300.
Vander Roost J, Daae FL, Steen IH, et al. (2018) Distribution patterns of iron-oxidizing Zeta-And Beta-proteobacteria from different environmental settings at the Jan Mayen Vent Fields. Front Microbiol 9:3008.
Van Kaam-Peters HME, and Sinninghe Damsté JS (1997) Characterisation of an extremely organic sulphur-rich, 150Ma old carbonaceous rock: palaeoenvironmental implications. Organ Geochem 27:371-397.
Vítek P, Jehlicka J, Edwards HGM, et al. (2009) Identification of b-carotene in an evaporitic matrix-evaluation of Raman spectroscopic analysis for astrobiological research on Mars. Anal Bioanal Chem 393:1967-1975.
Wang A, Freeman JJ, and Jolliff BL (2015) Understanding the Raman spectral features of phyllosilicates. J Raman Spectrosc 46:829-845.
Westall F and Cavalazzi B (2011) Biosignatures in rocks. In Encyclopedia of Geobiology, edited by V Thiel and J Reitner. Springer, Berlin, pp 189-201.
White SN (2009) Laser Raman spectroscopy as a technique for identification of seafloor hydrothermal and cold seep minerals. Chem Geol 259:240-252.
Wiens RC, Rull F, and Maurice S (2017) The SuperCam remote sensing instrument suite for the Mars 2020 rover mission: A preview. Spectroscopy 32:50-55.
Wiercigroch E, Szafraniec E, Czamara K, et al. (2017) Raman and infrared spectroscopy of carbohydrates: A review. Spectrochim Acta A Mol Biomol Spectrosc 185:317-335.
Williams AJ, Sumner DY, Alpers CN, et al. (2015) Preserved filamentous microbial biosignatures in the Brick Flat gossan, Iron Mountain, California. Astrobiology 15: 637-668.
Williford KH, Farley KA, Stack KM, et al. (2018) The NASA Mars 2020 rover mission and the search for extraterrestrial life. In From Habitability to Life on Mars, edited by N. Cabrol and E. Grin. Elsevier, Amsterdam, Netherlands, pp 275-308.
Zhou X, Chen D, Tang D, et al. (2015) Biogenic iron-rich filaments in the quartz veins in the uppermost Ediacaran Qigebulake Formation, Aksu area, northwestern Tarim basin, China: implications for iron oxidizers in subseafloor hydrothermal systems. Astrobiology 15:523-537.
