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Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures

Thomas-Keprta, Kathie L. and Clemett, Simon J. and Bazylinski, Dennis A. and Kirschvink, Joseph L. and McKay, David S. and Wentworth, Susan J. and Vali, Hojatollah and Gibson, Everett K., Jr. and McKay, Mary Fae and Romanek, Christopher S. (2001) Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures. Proceedings of the National Academy of Sciences of the United States of America, 98 (5). pp. 2164-2169. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:20130125-161546522

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Abstract

McKay et al. [(1996) Science 273, 924–930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe3O4) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.


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http://dx.doi.org/10.1073/pnas.051500898 DOIUNSPECIFIED
http://www.pnas.org/content/98/5/2164PublisherUNSPECIFIED
Additional Information:© 2001 National Academy of Sciences. Edited by Bruce Watson, Rensselaer Polytechnic Institute, Troy, NY, and approved December 18, 2000 (received for review October 22, 2000). We thank J. Hultberg of the National Aeronautics and Space Administration (NASA)/Johnson Space Center Scientific and Technical Information center, R. Christoffersen, T. D. Raub, R. N. Zare, P. R. Buseck, S. Keprta, K. White, R. B. Frankel, and the Honorable T. Campbell. We also thank J. Kulick and A. Jacobson of the Materials Research Science and Engineering Center at the University of Houston. We acknowledge the funding and support of NASA’s Astrobiology Institute and the Exobiology Program. D.A.B. was supported by the National Science Foundation
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NASA Astrobiology InstituteUNSPECIFIED
NASA Exobiology ProgramUNSPECIFIED
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Record Number:CaltechAUTHORS:20130125-161546522
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130125-161546522
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ID Code:36607
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:28 Jan 2013 15:36
Last Modified:25 Mar 2014 06:30

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