No ‘nanofossils’ in martian meteorite

Bradley, J. P.; Harvey, R. P.; McSween, H. Y.; Gibson, E. K.; Thomas‐Keprta, Kathie L.; Vali, Hojatollah

doi:10.1038/37257

Cited by 132 publications

(27 citation statements)

References 11 publications

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“…Apart from their similar sizes, aspect ratios, and shapes, both are found on the surfaces of carbonates within fracture zones. Published SEM images of aligned nanofossils (e.g., Kerr, 1997a) are likely either magnetite whiskers with parallel orientations resulting from epitaxial growth on the carbonates or emergent pyroxene or carbonate lamellae with "worm like" segmented surfaces enhanced by conductive heavy-metal coatings (Bradley et al, 1997;Kerr, 1997b). In describing nanofossils, Gibson et al (1997) noted that several forms contained dark, internal boundaries and suggested that they "appear to be dividing."…”

Section: Implications For Martian Biologymentioning

confidence: 99%

Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: Implications for biogenic mineralization

Bradley

McSween

Harvey

1998

Meteorit & Planetary Scien

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Abstract-Crystallographic relationships between magnetite, sulfides, and carbonate rosettes in fracture zones of the Allan Hills (ALH) 84001 Martian meteorite have been studied using analytical electron microscopy. We have focused on those magnetite grains whose growth mechanisms can be rigorously established from their crystallographic properties. Individual magnetite nanocrystals on the surfaces of carbonates are epitaxially intergrown with one another in "stacks" of single-domain crystals. Other magnetite nanocrystals are epitaxially intergrown with the surfaces of the carbonate substrates. The observed magnet- with lattice mismatches of -13% and -11%, respectively. Epitaxy is a common mode of vapor-phase growth of refractory oxides like magnetite, as is the spiral growth about axial screw dislocations previously observed in other magnetite nanocrystals in ALH 84001. Epitaxy rules out intracellular precipitation of these magnetites by (Martian) organisms, provides hrther evidence of the high-temperature (> 120 "C) inorganic origins of magnetite in ALH 84001, and indicates that the carbonates also have been exposed to elevated temperatures.

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Section: Implications For Martian Biologymentioning

confidence: 99%

Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: Implications for biogenic mineralization

Bradley

McSween

Harvey

1998

Meteorit & Planetary Scien

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“…The biological nature of these objects, however, has been challenged by both the geological and microbiological communities. The main objections are that these forms may have several possible abiotic origins, e.g., amorphous materials, etched crystallographic edges, and heavy-metal coating artifacts (4), and that they are too small to be living autonomous cells (15). Despite the interest associated with those problems, only a few studies have been carried out for characterizing the exact chemical composition and structure of such objects (e.g., refs.…”

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confidence: 99%

“…[1][2][3][4][5]. Consecutive to the suggestion by McKay et al (6) that ALH84001 contained evidence of Martian fossil life, several biogenicity criteria that can be checked with scanning electron microscopy (SEM) observations were discussed (e.g., refs.…”

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confidence: 99%

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite

Benzerara

Menguy

Guyot

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

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“…39,40 An awareness of this potential problem, when the search for evidence of microfossils in carbonaceous meteorites was initiated at NASA/MSFC in late 1996, an Environmental Scanning Electron Microscope (ESEM) was employed. The ESEM was chosen for the primary reason that uncoated and non-conductive samples could be studied and high spatial resolution images at high magnifications obtained without charging effects.…”

Section: Discussionmentioning

confidence: 99%

Filaments in carbonaceous meteorites: mineral crystals, modern bio-contaminants or indigenous microfossils of trichomic prokaryotes?

Hoover

Rozanov

2011

SPIE Proceedings

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Environmental (ESEM) and Field Emission Scanning Electron Microscopy (FESEM) investigations have resulted in the detection of a large number of complex filaments in a variety of carbonaceous meteorites. Many of the filaments were observed to be clearly embedded the rock matrix of freshly fractured interior surfaces of the meteorites. The high resolution images obtained combined with tilt and rotation of the stage provide 3-dimensional morphological and morphometric data for the filaments. Calibrated Energy Dispersive X-ray Spectroscopy (EDS) and 2-D elemental X-ray maps have provided information on the chemical compositions of the filaments and the minerals of the associated meteorite rock matrix. These observations are used to evaluate diverse hypotheses regarding the possible abiotic or biogenic nature of the filaments found embedded in these meteorites.

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No ‘nanofossils’ in martian meteorite

Cited by 132 publications

References 11 publications

Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: Implications for biogenic mineralization

Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: Implications for biogenic mineralization

Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite

Filaments in carbonaceous meteorites: mineral crystals, modern bio-contaminants or indigenous microfossils of trichomic prokaryotes?

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