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Published December 1, 2000 | public
Journal Article

Elongated prismatic magnetite crystals in ALH84001 carbonate globules: Potential Martian magnetofossils


Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe_3O_4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment. In this study, we describe six properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria), properties that, collectively, are not observed in any known population of inorganic magnetites. These criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories. Of the ALH84001 magnetites that we have examined, the elongated prismatic magnetite particles (∼27% of the total) are indistinguishable from the MV-1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals.

Additional Information

© 2000 Elsevier Science Ltd. Received December 7, 1999; accepted in revised form May 30, 2000. Special handling: C. Koeberl. We thank R.N. Zare, P. R. Buseck, H. Stanjek, R. B. Frankel, L. P. Keller, A. P. Taylor, and J. P. Bradley for constructive critical comments and the STI Center at Johnson Space Center, particularly J. Hultberg, for assistance. We thank B. Moskowitz, B. A. Hofmann, and an anonymous reviewer for greatly improving this manuscript. We also acknowledge the support of K. A. White, S. R. Keprta, M. F. McKay, The Honorable Tena Camp Bell, and D. C. Golden. We acknowledge the funding and support of NASA's Astrobiology and Exobiology Programs. DAB was also supported by United States National Science Foundation (NSF) grant CHE-9714101.

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