Elongated prismatic magnetite crystals in ALH84001 carbonate globules:

Thomas‐Keprta, Kathie L.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; Clemett, S. J.; McKay, D. S.; Wentworth, S. J.; Vali, Hojatollah; Gibson, E. K.; Romanek, Christopher S.

doi:10.1016/s0016-7037(00)00481-6

Cited by 278 publications

(247 citation statements)

References 161 publications

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“…5C). This is similar to our previous observation of Al and Cr in some magnetites liberated by acid dissolution of ALH84001 carbonate (Thomas-Keprta et al, 2000a). In that instance, Treiman (2003) argued that the Al and/or Cr may have been present as an unobserved Fe-bearing phyllosilicate surface coating.…”

Section: Impure Alh84001 Magnetitesupporting

confidence: 90%

“…Compositional analyses by EDX showed that the vast majority of these magnetites (>95%) were stoichiometrically pure Fe 3 O 4 within detection limits 7 (Thomas-Keprta et al, 2000a). While this approach yields an abundant population of magnetites for analysis, all information on their distribution within the host carbonate was lost.…”

Section: Stoichiometrical 'Pure' Alh84001 Magnetitementioning

confidence: 98%

“…Embedded within these carbonates are discrete nanocrystal magnetites (Fe 3 O 4 ) that exhibit super-paramagnetic to single-domain properties (Muxworthy and Williams, 2008). While the largest population of these magnetites occurs within the rim zone of the carbonate disks, e.g., McKay et al (1996) and Thomas-Keprta et al (2000a), a small but significant fraction is also found within the inner and outer core zones.…”

Section: Introductionmentioning

confidence: 99%

“…We have then used these new observations to evaluate the merits of both theoretical and experimental attempts to reproduce ALH84001-like disks with embedded magnetites through partial thermal decomposition of Fe-bearing carbonate. In the larger context, resolving or at least constraining the origin of the magnetites within ALH84001 carbonate disks has importance in that it has been previously suggested that the precipitation of the carbonate disks may have been facilitated through biogenic activity (McKay et al, 1996) and that a fraction of the embedded magnetites exhibit chemical and physical features identical to those produced by contemporary magnetotactic bacteria (McKay et al, 1996;Thomas-Keprta et al, 2000a;Thomas-Keprta et al, 2001;Thomas-Keprta et al, 2002). Table 1 lists the ALH84001 rock splits used in the research presented herein.…”

Section: Introductionmentioning

confidence: 99%

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Origins of magnetite nanocrystals in Martian meteorite ALH84001

Thomas‐Keprta

Clemett

McKay

et al. 2009

Geochimica et Cosmochimica Acta

108

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The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe 3 O 4 ) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any shock or thermal processing of the carbonates.

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Section: Impure Alh84001 Magnetitesupporting

confidence: 90%

Section: Stoichiometrical 'Pure' Alh84001 Magnetitementioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Origins of magnetite nanocrystals in Martian meteorite ALH84001

Thomas‐Keprta

Clemett

McKay

et al. 2009

Geochimica et Cosmochimica Acta

108

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“…Magnetite biomineralization by magnetotactic bacteria is a topic of great interest in nanotechnology [7][8][9][10][11][12] , functional materials [11][12][13][14][15][16] , and astrobiology 17 . Magnetotactic bacteria take up soluble iron species that they use to biomineralize chains of magnetite nanocrystals, known as magnetosomes, in intracellular membrane vesicles 2 .…”

mentioning

confidence: 99%

Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

et al. 2015

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Magnetotactic bacteria biomineralize ordered chains of uniform, membrane-bound magnetite or greigite nanocrystals that exhibit nearly perfect crystal structures and species-specific morphologies. Transmission electron microscopy (TEM) is a critical technique for providing information regarding the organization of cellular and magnetite structures in these microorganisms. However, conventional TEM can only be used to image air-dried or vitrified bacteria removed from their natural environment. Here we present a correlative scanning TEM (STEM) and fluorescence microscopy technique for imaging viable cells of Magnetospirillum magneticum strain AMB-1 in liquid using an in situ fluid cell TEM holder. Fluorescently labeled cells were immobilized on microchip window surfaces and visualized in a fluid cell with STEM, followed by correlative fluorescence imaging to verify their membrane integrity. Notably, the post-STEM fluorescence imaging indicated that the bacterial cell wall membrane did not sustain radiation damage during STEM imaging at low electron dose conditions. We investigated the effects of radiation damage and sample preparation on the bacteria viability and found that approximately 50% of the bacterial membranes remained intact after an hour in the fluid cell, decreasing to ,30% after two hours. These results represent a first step toward in vivo studies of magnetite biomineralization in magnetotactic bacteria.B iomineralization is a widespread biological phenomenon occurring in living organisms ranging from single cells to complex multicellular organisms. Biomineralization of inorganic materials in single cell organisms is an ideal system for studying fundamental mechanisms of biomineralization 1 . Model systems range from prokaryotic organisms, such as magnetite formation in magnetotactic bacteria 2-4 , to eukaryotic organisms, such as silica biomineralization in diatoms 5,6 . Understanding biomineralization in these organisms in terms of crystal nucleation and growth, as well as the involvement of biological macromolecules and cellular processes, is of fundamental interest to scientists as similar principles can be used to develop synthetic nanomaterials.Magnetite biomineralization by magnetotactic bacteria is a topic of great interest in nanotechnology 7-12 , functional materials [11][12][13][14][15][16] , and astrobiology 17 . Magnetotactic bacteria take up soluble iron species that they use to biomineralize chains of magnetite nanocrystals, known as magnetosomes, in intracellular membrane vesicles 2 . The nanocrystals have nearly perfect mineral crystal structures with consistent species-specific morphologies, leading to well-defined magnetic properties 2,3,9,12,18,19 . As a result, magnetotactic bacteria are one of the best model systems for investigating the molecular mechanisms of biomineralization. Magnetite biomineralization in these bacteria is a complex process involving a number of steps including cellular uptake and reduction of ferric ions, complexation of the iron with membrane proteins, an...

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Geochemical and Geological Significance of Subsurface Microbiology

Onstott

2003

Encyclopedia of Environmental Microbiology

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Elongated prismatic magnetite crystals in ALH84001 carbonate globules:

Cited by 278 publications

References 161 publications

Origins of magnetite nanocrystals in Martian meteorite ALH84001

Origins of magnetite nanocrystals in Martian meteorite ALH84001

Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

Geochemical and Geological Significance of Subsurface Microbiology

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