Magnetite morphology and life on Mars

Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from the Martian meteorite. In contrast to previous accounts, we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars.

[1]  R. Frankel,et al.  Magnetite biomineralization and ancient life on Mars. , 2000, Current opinion in chemical biology.

[2]  D. Veblen,et al.  A TEM study of fibrous cuprite (chalcotrichite); microstructures and growth mechanisms , 1983 .

[3]  R. Frankel,et al.  Electron microscopy study of magnetosomes in a cultured coccoid magnetotactic bacterium , 1993, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[4]  T. Matsuda,et al.  Morphology and structure of biogenic magnetite particles , 1983, Nature.

[5]  M. F. Mckay,et al.  Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[6]  H. V. Lauer,et al.  Letter. A simple inorganic process for formation of carbonates, magnetite, and sulfides in martian meteorite ALH84001 , 2001 .

[7]  Peter R. Buseck,et al.  Magnetite from magnetotactic bacteria; size distributions and twinning , 1998 .

[8]  R. Egerton.  Electron Energy-Loss Spectroscopy in the Electron Microscope , 1995, Springer US.

[9]  Frankel,et al.  Magnetic microstructure of magnetotactic bacteria by electron holography , 1998, Science.

[10]  J. Kirschvink,et al.  Elongated prismatic magnetite crystals in ALH84001 carbonate globules: potential Martian magnetofossils. , 2000, Geochimica et cosmochimica acta.

[11]  Carmen Ascaso,et al.  Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[12]  W. Baumeister,et al.  Perspectives of molecular and cellular electron tomography. , 1997, Journal of structural biology.

[13]  R. Frankel,et al.  Off-axis electron holography of magnetotactic bacteria: magnetic microstructure of strains MV-1 and MS-1 , 2001 .

[14]  R. Frankel,et al.  Crystal-size distributions and possible biogenic origin of Fe sulfides , 2001 .

[15]  A. Verkleij,et al.  Three-Dimensional Transmission Electron Microscopy: A Novel Imaging and Characterization Technique with Nanometer Scale Resolution for Materials Science , 2000 .

[16]  R. Frankel,et al.  Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium , 1990 .

[17]  F. Donald Bloss,et al.  Crystallography And Crystal Chemistry , 1971 .

[18]  C. Klein,et al.  Manual of mineralogy , 1864 .

[19]  R. Zare,et al.  Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 , 1996, Science.

[20]  H. McSween,et al.  Magnetite whiskers and platelets in the ALH84001 Martian meteorite: evidence of vapor phase growth. , 1996, Geochimica et cosmochimica acta.

[21]  R. Blakemore,et al.  Structure, morphology and crystal growth of anisotropic magnetite crystals in magnetotactic bacteria , 1987, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[22]  R. Blakemore,et al.  Structure, morphology and crystal growth of bacterial magnetite , 1984, Nature.

[23]  A. P. Taylor,et al.  Structural and morphological anomalies in magnetosomes: possible biogenic origin for magnetite in ALH84001 , 2001, Journal of microscopy.

[24]  Ar Lang,et al.  International Tables for Crystallography, Vol C , 1992 .

[25]  R. Frankel,et al.  Magnetic Microstructure of Bacterial Magnetite by Electron Holography , 2001 .

[26]  T. Hahn.  International tables for crystallography , 2002 .

[27]  A. F. Rogers.  A tabulation of crystal forms and discussion of form-names , 1935 .