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Determination of the Three-Dimensional Morphology of ALH84001 and Biogenic MV-1 Magnetite: Comparison of Results from Electron Tomography and Classical Transmission Electron MicroscopyDated at approximately 3.9 billion years of age, carbonate disks, found within fractures of the host rock of Martian meteorite ALH84001, have been interpreted as secondary minerals that formed at low temperature in an aqueous medium. Heterogeneously distributed within these disks are magnetite nanocrystals that are of Martian origin. Approximately one quarter of these magnetites have morphological and chemical similarities to magnetite particles produced by magnetotactic bacteria strain MV-1, which are ubiquitous in aquatic habitats on Earth. Moreover, these types of magnetite particles are not known or expected to be produced by abiotic means either through geological processes or synthetically in the laboratory. The remaining three quarters of the ALH84001 magnetites are likely products of multiple processes including, but not limited to, precipitation from a hydrothermal fluid, thermal decomposition of the carbonate matrix in which they are embedded, and extracellular formation by dissimilatory Fe-reducing bacteria. We have proposed that the origins of magnetites in ALH84001 can be best explained as the products of multiple processes, one of which is biological. Recently the three-dimensional (3-D) external morphology of the purported biogenic fraction of the ALH84001 magnetites has been the subject of considerable debate. We report here the 3-D geometry of biogenic magnetite crystals extracted from MV-1 and of those extracted from ALH84001 carbonate disks using a combination of high resolution classical and tomographic transmission electron microscopy (TEM). We focus on answering the following questions: (1) which technique provides adequate information to deduce the 3-D external crystal morphology?; and, (2) what is the precise 3-D geometry of the ALH84001 and MV-1 magnetites?
Document ID
20040065801
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Thomas-Keprta, Kathie L. (Lockheed Martin Space Operations Houston, TX, United States)
Clemett, Simon J. (Lockheed Martin Space Operations Houston, TX, United States)
Schwartz, Cindy (Colorado Univ. Boulder, CO, United States)
Morphew, Mary (Colorado Univ. Boulder, CO, United States)
McIntosh, J. Richard (Colorado Univ. Boulder, CO, United States)
Bazylinski, Dennis A. (Iowa State Univ. of Science and Technology Ames, IA, United States)
Kirschvink, Joseph L. (California Inst. of Tech. Pasadena, CA, United States)
Wentworth, Susan J. (Lockheed Martin Space Operations Houston, TX, United States)
McKay, David S. (NASA Johnson Space Center Houston, TX, United States)
Vali, Hojatollah (McGill Univ. Montreal, Quebec, Canada)
Date Acquired
August 21, 2013
Publication Date
January 1, 2004
Publication Information
Publication: Lunar and Planetary Science XXXV: Astrobiology
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
JSC-CN-8386
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20040065785Collected WorksLunar and Planetary Science XXXV: Astrobiology
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