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Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignaturesMcKay 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 (Fe(3)O(4)) 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.
Document ID
20040112542
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Thomas-Keprta, K. L.
(NASA Headquarters Washington, DC United States)
Clemett, S. J.
Bazylinski, D. A.
Kirschvink, J. L.
McKay, D. S.
Wentworth, S. J.
Vali, H.
Gibson, E. K. Jr
McKay, M. F.
Romanek, C. S.
Date Acquired
August 21, 2013
Publication Date
February 27, 2001
Publication Information
Publication: Proceedings of the National Academy of Sciences of the United States of America
Volume: 98
Issue: 5
ISSN: 0027-8424
Subject Category
Lunar And Planetary Science And Exploration
Distribution Limits
Public
Copyright
Other

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