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The 3.466 Ga “Kitty's Gap Chert,” an early Archean microbial ecosystem

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Frances Westall
Frances Westall
Centre de Biophysique Moléculaire, CNRS, Rue Charles Sadron, 45071 Orléans cedex 2, France
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Sjoukje T. de Vries
Sjoukje T. de Vries
Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
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Wouter Nijman
Wouter Nijman
Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
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Virgile Rouchon
Virgile Rouchon
Département des Sciences de la Terre, UMR CNRS-UPS Interaction and Dynamics of Surface Environments, Université Paris Sud, Bât. 504, 91405 Orsay Cedex, France and Planetary Science Laboratory, Osaka University, 1-1 Machikaneyama, Toyonaka, 560-0043 Osaka, Japan
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Beate Orberger
Beate Orberger
Département des Sciences de la Terre, UMR CNRS-UPS Interaction and Dynamics of Surface Environments, Université Paris Sud, Bât. 504, 91405 Orsay Cedex, France
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Victoria Pearson
Victoria Pearson
Planetary and Space Sciences Research Institute (PSSRI), The Open University, Walton Hall, Milton Keynes, K7 6AA, UK
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Jon Watson
Jon Watson
Planetary and Space Sciences Research Institute (PSSRI), The Open University, Walton Hall, Milton Keynes, K7 6AA, UK
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Alexander Verchovsky
Alexander Verchovsky
Planetary and Space Sciences Research Institute (PSSRI), The Open University, Walton Hall, Milton Keynes, K7 6AA, UK
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Ian Wright
Ian Wright
Planetary and Space Sciences Research Institute (PSSRI), The Open University, Walton Hall, Milton Keynes, K7 6AA, UK
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Jean-Noël Rouzaud
Jean-Noël Rouzaud
Centre de la Matière Divisée, CNRS, 1B rue de la Férollerie, 45071 Orléans cedex 2, France
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Daniele Marchesini
Daniele Marchesini
via Torino 10, 40139 Bologna, Italy
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Anne Severine
Anne Severine
Department of Geological Sciences, University of Orléans, 45071 Orléans cedex 2, France
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Published:
January 01, 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 μm and 0.75–0.8 μm. 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 biofilms 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 μm in width and rare, short rods 1 μm in length. Carbon isotopic compositions of about −26‰ to −30‰, 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.

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Contents

GSA Special Papers

Processes on the Early Earth

Wolf Uwe Reimold
Wolf Uwe Reimold
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Roger L. Gibson
Roger L. Gibson
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Geological Society of America
Volume
405
ISBN print:
9780813724058
Publication date:
January 01, 2006

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