%0 Journal
%T Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures
%A 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 and McKay, Mary Fae and Romanek, Christopher S
%J Proceedings of the National Academy of Sciences
%V 98
%P 2164--2169
%D 2001
%R doi.org/10.1073/pnas.051500898
%X 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.