2015 Annual Science Report

University of Wisconsin Reporting  |  JAN 2015 – DEC 2015

Project 3D: SIMS Analyses of Filamentous Fossil Microbes From the ~3,465 Ma-Old Apex Chert May Reveal Their Physiology

Project Summary

Permineralized carbonaceous filamentous fossils of the ~3465 Ma Apex chert of Western Australia are among the oldest known in the geological record. Eleven taxa of Bacteria Incertae Sedis (microbes of uncertain systematic affinities) have been described from this assemblage, defined on the basis of the medial and terminal cell size and shape of 200 specimens. To assess their physiology and, thus, their biological affinities, 20 additional specimens, referable to six of the taxa, have been prepared in thin section. Samples will be cut out and repolished to expose each microfossil individually for δ13C analyses by use of secondary ion mass spectroscopy (SIMS). Their carbonaceous composition has been mapped by Raman spectroscopy and, as applicable, by confocal laser scanning microscopy, CLSM. This is the first study to use optical microscopy, Raman spectroscopy, SIMS and CLSM, to analyze multiple individual microscopic fossils from a single deposit — applied here to among the oldest fossils now known in the geological record.

4 Institutions
3 Teams
4 Publications
0 Field Sites
Field Sites

Project Progress

Our previous studies have established that the ~3465 Ma Apex filaments are bona fide fossils. That the fossils are indigenous to the Apex chert – rather than being contaminants – is established by their occurrence within petrographic thin sections, in which they are three-dimensionally permineralized (Schopf, 1993; Schopf and Kudryavtsev, 2013). That they are syngenetic with the formation of the enclosing chert – rather than being later introduced — is shown by their occurrence in carbonaceous clasts, their absence from vein-fillings, and by the identical geochemical maturity and their carbonaceous components to that of associated particulate kerogen and the SIMS-determined δ13C composition of such kerogen (Morag et al., 2015a, 2015b, 2016; Schopf, 1993; Schopf and Kudryavtsev, 2012). And that they are biogenic is shown by the preservation of cells, their carbonaceous composition, the occurrence of numerous specimens (if one fossil is preserved, others should be also) and their morphological similarity to other fossil and living microorganisms (Schopf, 1993; Schopf and Kudryavtsev, 2012).

The 20 fossils to be analyzed by SIMS are members of the originally described Apex biological community. All have been optically, Raman- and CLSM-analyzed in a petrographic thin section (4 of 6/15/82-1H) of the same rock from which the fossils were originally described (viz., 4 of 6/15/82, Sections 1A to 1G – archived at the Natural History Museum, London, and thus impermissible for SIMS analysis). Eighteen of the fossils exhibit morphology establishing their placement in six previously described taxa (Primaevifilum minutum, 4 specimens; P. delicatulum, 4; P. amoenum, 2; cf. P. conicoterminatum, 2; Archaeoscillatoriopsis disciformis, 4; A. grandis, 2). Two additional previously undescribed unicellular fossils have been similarly prepared. Representative specimens prepared for SIMS analyses are show in Figures 1-6.

Figure 1-6. Optical photomicrographs (1, 3, 5), Raman kerogen two-dimensional images (2, 4), and a confocal laser scanning micrograph (6) of representative specimens of the 20 Apex fossils that have been prepared for SIMS analysis: 1, 2, Primaevifilum amoenum; 3, 4, Archaeoscillatoriopsis disciformis ; 5, 6, P. minutum.

Our SIMS analyses of multiple individual specimens of these seven different Apex morphotypes will provide a basis to assess taxon-related δ13C compositions, to determine the physiology of diverse members of this exceptionally ancient microbial assemblage, and to provide additional evidence of biogenicity (cf. Schopf et al., 2015; Williford et al., 2015a, b, c, d).

References Cited
Morag N, Kenneth H. Williford, Kouki Kitajima, Pascal Philippot, Martin J. Van Kranendonk, Kevin Lepot, and John W. Valley, (2015a) Microstructure-Specific Carbon Isotopic Signature Of Organic Matter Supports Biologic Origin in 3.5 GA Cherts Of The Pilbara Craton. AbGradCon 2015, Madison, Wisconsin.

Morag, N, Kenneth H. Williford, Kouki Kitajima, Pascal Philippot, Martin J. Van Kranendonk, Kevin Lepot, John W. Valley (2015b) Microstructure-Specific Carbon Isotopic Signature Of Organic Matter Supports Biologic Origin In ~3.5 Ga Cherts Of The Pilbara Craton. Astrobiol. Sci. Conf. June 17, 2015. Chicago.

Morag N, Williford KH, Kitajima K, Philippot P, Van Kranendonk MJ, Lepot K, Thomazo C, Valley JW (2016) Microstructure-specific carbon isotopic signatures of organic matter from ~3.5 Ga cherts of the Pilbara Craton support a biologic origin, PreCamb Res, accepted.

Schopf, J.W (1993) Microfossils of the Early Archean Apex chert: new evidence of the antiquity of life. Science 260:640-646.

Schopf, JW and Kudryavtsev, AB (2012) Biogenicity of Earth’s earliest fossils: a resolution of the controversy. Gondwana Research 39:761-771.

Schopf JW, Kudryavtsev AB, Walter MW, Van Kranendonk MJ, Williford KH, Kozdon R, Valley JW, Gallardo VA, Espinoza C, Flannery DT (2015) A fossil sulfur-cycling microbiota from the 1.8 Ga Duck Creek Formation provides promising evidence of evolution’s null hypothesis. PNAS. doi:10.1073/pnas.1419241112.

Williford KH, Ushikubo T, Lepot K, Kitajima K, Hallmann C, Spicuzza MJ, Kozdon R, Eigenbrode JL, Summons RE, Valley JW (2015a) Isotopic signatures of ancient life and environment at the microbial scale: Neoarchean shales and carbonates. Geobiology, DOI: 10.1111/gbi.12163.

Williford KH, Ushikubo T, Lepot K, Kitajima K, Hallmann C, Spicuzza MJ, Kozdon R, Eigenbrode JL, Summons RE, Valley JW (2015b) Isotopic signatures of ancient life and environment at the microbial scale: Neoarchean shales and carbonates. Geobiology, DOI: 10.1111/gbi.12163.

Williford KH, Ushikubo T, Sugitani K, Lepot K, Kita NT, Van Kranendonk MJ (2015c) A new isotopic biosignature of Paleoarchean sulfur metabolism, Goldschmidt Conf., Prague.

Williford KT, T. Ushikubo, K. Sugitani, K., Lepot, K. Kitajima, K. Mimura, J. W. Valley (2015d) A sulfur four-isotope signature of Paleoarchean metabolism. Astrobiol. Sci. Conf., June 18, 2015. Chicago.