LOGIN TO YOUR ACCOUNT

Username
Password
Remember Me
Or use your Academic/Social account:

CREATE AN ACCOUNT

Or use your Academic/Social account:

Congratulations!

You have just completed your registration at OpenAire.

Before you can login to the site, you will need to activate your account. An e-mail will be sent to you with the proper instructions.

Important!

Please note that this site is currently undergoing Beta testing.
Any new content you create is not guaranteed to be present to the final version of the site upon release.

Thank you for your patience,
OpenAire Dev Team.

Close This Message

CREATE AN ACCOUNT

Name:
Username:
Password:
Verify Password:
E-mail:
Verify E-mail:
*All Fields Are Required.
Please Verify You Are Human:
fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Publisher: Cambridge University Press
Languages: English
Types: Article
Subjects: QE, QK
Structures, termed microbioids, comforming to bacteria in size and shape (e.g. rods, spheres, chains and clusters of spheres) have been observed by field emission scanning electron microscopy (FE-SEM) on coalified Silurian and Lower Devonian spores, sporangia, cuticles and coprolites. Some were sectioned for transmission electron microscopy. The elemental composition of both microbioids and ‘substrates’ was investigated using a X-ray microanalysis system. These analyses combined with comparative studies on recent bacteria and cyanobacteria were undertaken to evaluate the biogenicity, nature and age of the microbioids. Spheres with a Si signature (0.03–0.5 μm diameter) and assumed composed of silica are interpreted as artefacts produced abiotically during the extraction procedures. A similar origin is proposed for hollow spheres that are composed of CaF2. These occur singly, in short chains simulating filaments, and in clusters. Considerable differences in size (0.2–2.0 μm diameter) and appearance relate to local variation in the chemical environment during extraction. Spheres (0.2–1.5 μm diameter), that lack a mineral signature, with a framboidal surface ornament and occur within sporangia are identified as by-products of spore development. A biotic origin is also postulated for C-containing rod-shaped structures (>3.1 μm long, <1.4 μm wide), some with collapsed surfaces, although comparisons with living bacteria indicate recent contamination. More elongate rod-shaped microbioids (<8.6 μm long, 1.2 μm wide) have been identified as detrital rutile crystals (TiO2). Minute naviculate structures (<2.2 μm long) resembling diatoms are of unknown origin but are probably composed of thorium hydroxide. Unmineralized filaments of cyanobacterial morphology are recent contaminants. Some of the sporangia and spore masses are partially covered by associations of fragmented sheets, interconnecting strands, rods and spheres that are interpreted as dehydrated biofilms. Being unmineralized they are probably also of recent origin, although they might have survived wild-fire along with the charcoalified mesofossils. Many of the structures illustrated here were initially identified casually as bacteria on the small fossils extracted for biodiversity studies using well-tried, conventional, palaeobotanical techniques. Our subsequent more detailed analyses have shown how such processes can produce artefacts that are morphological analogues of mineralized bacteria, leave residues that mimic bacterial shapes and, despite some efforts such as storage in dilute HCl to eliminate living bacteria, introduce contamination. They reinforce previous concerns that verification of the biogenicity and syngenicity of bacterial-like objects in ancient Earth and extra-terrestrial rocks should not only rely on size and morphological look-alikes, but must encompass a thorough understanding of fossilization processes and extraction techniques plus, ideally, other measures of biogenicity (e.g. biomarkers) and syngenicity.
  • The results below are discovered through our pilot algorithms. Let us know how we are doing!

    • Bradley, W.H. (1963). Unmineralized fossil bacteria. Science 141, 919-921.
    • Bradley, W.H. (1968). Unmineralized fossil bacteria : a retraction. Science 160, 437.
    • Brasier, M.D., Green, O.R., Jephcoat, A.P., Kleppe, A.K., van Kranendonk, M.J., Lindsay, J.F., Steele, A. & Grassineau, N.V. (2002). Questioning the evidence for the Earth's oldest fossils. Nature 416, 76-81.
    • Brasier, M.D., Green, O.R., Lindsay, J.F., McLoughlin, N., Steele, A. & Stoakes, C. (2005). Critical testing of Earth's oldest putative fossil assemblage from the y3.5 Ga Apex chert, Chinaman Creek, Western Australia. Precambrian Research 140, 55-102.
    • Briggs, D.E.G. (2003). The role of biofilms in the fossilization of nonbiomineralized tissues. In Fossil and Recent Biofilms. A Natural History Liebig, K., Westall, F. & Schmitz, M. (1996). A study of fossil microstructures from the Eocene Messel Formation using transmission electron microscopy. Neues Jahrbuch fu¨r Geologie und Pala¨ontologie Monatshefte 4, 218-231.
    • Martill, D.M. (1987). Prokaryote mats replacing soft tissues in Mesozoic marine reptiles. Modern Geology 11, 265-269.
    • Martill, D.M. & Wilby, P.R. (1994). Lithified prokaryotes associated with fossil soft tissues from the Santana Formation (Cretaceous) of Brazil. Kaupia 4, 71-77.
    • Martin, D., Briggs, D.E.G. & Parkes, R.J. (2003). Experimental mineralization of invertebrate eggs and the preservation of Neoproterozoic embryos. Geology 31, 39-42.
    • McKay, D.S., Gibson Jr., E.K. Thomas-Keprta, K.L., Vali, H., Romanek, C.S., Clemett, S.J., Chillier, X.D.F., Maechling, C.R. & Zare, R.N. (1996). Search for past life on Mars : possible relic biogenic activity in Martian meteorite ALH 84001. Science 273, 924-930.
    • Nealson, K.H. (1997). Sediment bacteria : who's there, what are they doing, and what's new ? Ann. Rev. of Earth and Planetary Sci. Lett. 25, 403-434.
    • Oehler, J.H. & Schopf, J.W. (1971). Artificial microfossils : experimental studies of permineralization of blue-green algae in silica. Science 174, 1229-1231.
    • Pike, J. (2004). Personal communication.
    • Reynolds, E.S. (1963). The use of lead citrate at high pH as an electronopaque stain in electron microscopy. J. Cell Biology 17, 208-212.
    • Richter, G. (1994). Bacteria and bacteria-like structures from the oil-shale of Messel. Kaupia 4, 21-28.
    • Schopf, J.W. & Walter, M.R. (1983). Archean microfossils : new evidence of ancient microbes. In Earth's Earliest Biosphere, Its Origin and Evolution, ed. Schopf, J.W., pp. 214-239. Princeton University Press, Princeton.
    • Schopf, J.W., Kudryavtsev, A.B., Agresti, D.G., Wdowiak, T.J. & Czaja, A.D. (2002). Laser-Raman imagery of Earth's earliest fossils. Nature 416, 73-76.
    • Sillitoe, R.H., Folk, R.L. & Saric, N. (1996). Bacteria as mediators of copper sulfide enrichment during weathering. Science 272, 1153-1155.
    • Spurr, A.R. (1969). Low viscosity epoxy resin embedding medium for electron microscopy. J. Ultra. Res. 26, 31-43.
    • Thomas-Keprta, K.L., McKay, D.S., Wentworth, S.J., Stevens, T.O., Taunton, A.E., Allen, C.C., Coleman, A., Gibson, Jr., E.K. & Romanek, C.S. (1998). Bacterial mineralization patterns in basaltic aquifers : implications for possible life in martian meteorite ALH84001. Geology 26, 1031-1034.
    • Tschech, A. & Pfennig, N. (1984). Growth yield increase linked to caffeate reduction in Acetobacterium woodii. Arch. Microbiol. 137, 163-167.
    • Toporski, J.K.W., Steele, A., Westall, F., Thomas-Keprta, K.L. & McKay, D.S. (2002). The simulated silicification of bacteria - new clues to the modes and timing of bacterial preservation and implications for the search of extraterrestrial microfossils. Astrobiol. 2, 1-26.
    • Toporski, J., Steele, A., McKay, D.S. & Westall, F. (2003). Bacterial films in Astrobiology : the importance of life detection. In Fossil and Recent Biofilms. A Natural History of Life on Earth, eds Krumbein, W.E., Paterston, D.M. & Zavarzin, G.A., ch. 31, pp. 429-445. Kluwer Academic Publishers, Dordrecht/Boston/London.
    • Walters, C.C., Margulis, L. & Barghoorn, E.S. (1977) On the experimental silicification of microorganisms. I. Microbial growth on organosilicon compounds. Precambrian Research 5, 241-248.
    • Wellman, C.H., Edwards, D. & Axe, L. (1998a). Ultrastructure of laevigate hilate cryptospores in sporangia and spore masses from the Upper Silurian and Lower Devonian of the Welsh Borderland. Philos. Trans. Roy. Soc. London B353, 1983-2004.
    • Wellman, C.H., Edwards, D. & Axe, L. (1998b). Permanent dyads in sporangia and spore masses from the Lower Devonian of the Welsh Borderland. Bot. J. Linn. Soc. 127, 117-147.
    • Westall, F. (1994). Silicified bacteria and associated biofilm from the deep-sea sedimentary environment. Kaupia 4, 29-43.
    • Westall, F. (1999). The nature of fossil bacteria : a guide to the search for extraterrestrial life. J. Geophys. Res. 104, 16 437-16 451.
    • Westall, F. & Folk, R.L. (2003). Exogenous carbonaceous microstructures in Early Archaean cherts and BIFs from the Isua Greenstone Belt : implications for the search for life in ancient rocks. Precambrian Research 126, 313-330.
    • Westall, F. & Rince´ , Y. (1994). Biofilms, microbial mats and microbeparticle interactions : electron microscope observations from diatomaceous sediments. Sedimentology 41, 147-162.
    • Westall, F., Boni, L. & Guerzoni, E. (1995). The experimental silicification of microorganisms. Palaeontology 38, 495-528.
    • Westall, F., de Wit, M.J., Dann, J., van der Gaast, S., de Ronde, C.E.J. & Gerneke, D. (2001). Early Archean fossil bacteria and biofilms in hydrothermally-influenced sediments from the Barberton greenstone belt, South Africa. Precambrian Research 106, 93-116.
    • Whitman, W.B., Coleman, D.C. & Wiebe, W.J. (1998). Prokaryotes : the unseen majority. Proc. Nat. Acad. Sci. USA 95, 6578-6583.
    • Wilkinson, H.P. (2003). Fossil actinomycete filaments and fungal hyphae in dicotyledonous wood from the Eocene London Clay, Isleof-Sheppey, Kent, England. Bot. J. Linn. Soc. 142, 383-394.
    • 1b (cont.)
  • No related research data.
  • No similar publications.

Share - Bookmark

Cite this article