Biomarkers and Microfossils in the Murchison, Rainbow, and Tagish Lake meteorites

Hoover, Richard B.; Jerman, G. A.; Rozanov, A. Yu.; Davies, Paul

doi:10.1117/12.463321

Cited by 13 publications

(13 citation statements)

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“…1(c)). These features have also been found in Martian meteorite ALH84001 (McKay et al 1996) and in other carbonaceous chondrites (Hoover et al 2003;Hoover 2009). The melting process resulted in the formation of fusion crusts rich in Fe and Si and melt flakes of Fe-Ni composition.…”

Section: Discussionsupporting

confidence: 63%

Microstructural investigation of the Carancas meteorite

Rauf

Hann

Wickramasinghe

et al. 2010

International Journal of Astrobiology

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Particles in the Carancas meteorite were examined by electron microscopy (transmission electron microscopy/scanning electron microscopy), energy dispersive analysis of X-rays (EDAX) and Fourier Transform Infrared spectroscopy. Scanning electron microscopical observations reveal that the particles of variable sizes have a stony appearance. Many of these particles show fractures in places, thus confirming an ealier observation that the meteorite was subjected to a high-velocity impact. The outer rim of many aggregates displays a mud crack-like texture. At high magifications, this texture shows ovoid and elongated features, which appear similar to microfossils found in other meteorites.As revealed by both scanning and transmission electron microscopy, some particles show three clearly marked zones, distinguishable by their differences in electron density and texture : a light zone, a dark zone and an intermediate zone. The EDAX analysis of these particles shows that the light zone is composed of silicates rich in Fe, Ni and S (the elements of troilite and pentlandite). The dark zone contains high concentrations of Mg and Si (the major elements of high-temperature minerals, such as forsterite, Mg 2 SiO 4 and enstatite, MgSiO 3 ) intermixed with carbonates and traces of Al, Ca and Na. The intermediate zone also contains high-temperature minerals and Fe-Ni rich silicates.The Carancas meteorite produces an infrared waveband showing prominent features of some carbonate species, amorphous and crystalline silicates, and olivine groups. Hydrated silicates and hydroxyl groups are less abundant, as shown by the presence of small humps between 2.5 and 8.0 mm.The abundance of high-temperature minerals and iron-rich metal confirms an earlier observation that the meteorite is an ordinary H4/5 chondrite. Some particles in the Carancas meteorite are found to have structural and chemical characteristics similar to those of the 81P/Wild 2 comet.

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Section: Discussionsupporting

confidence: 63%

Microstructural investigation of the Carancas meteorite

Rauf

Hann

Wickramasinghe

et al. 2010

International Journal of Astrobiology

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“…7 During the past 14 years, many large, complex filaments, consortia and mat assemblages have been found with undeniable biological characteristics that were interpreted as indigenous microfossils in carbonaceous meteorites during both independent and collaborative SEM, ESEM and FESEM investigations carried out in the United States and Russia. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Many of the filamentous and coccoidal microstructures found during this research were consistent with forms found half a century ago by earlier researchers (e.g., Nagy, Claus, Fitch, Palik, Timofeyev and van Landingham) and interpreted as indigenous microfossils of blue-green algae (cyanophytes), bacteria, and acritarchs or dismissed as recent bacterial contaminants or pollen grains. [23][24][25][26][27][28][29][30][31][32] The filaments detected at NASA/MSFC were imaged with secondary and backscattered electron detectors and analyzed by EDS to obtain spot data and 2D x-ray maps at voltages ranging from 5 keV to 15 keV.…”

Section: Introductionsupporting

confidence: 75%

“…Coccoidal forms and filaments had been found in carbonaceous meteorites by earlier workers and interpreted as indigenous remains of algae, acritarchs, cyanobacteria or other filamentous trichomic prokaryotes. [5][6][7][8][9][10][11][12] Entirely independent SEM studies of the Murchison (CM2) and Efremovka (CO2) carbonaceous meteorites were carried out in Moscow by Rozanov and his co-workers at the Paleontological Institute (PIN) and at the Institute of Microbiology (INMI) of the Russian Academy of Sciences. They had detected a large suite filaments in entirely different samples from the meteorite collection of the Vernadsky Institute with similar sizes and morphologies to those found at NASA/MSFC.…”

Section: Introductionmentioning

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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“…34,35 Other possible biominerals in meteorites include the iron-rich framboids with precise monodisperse crystallites as were previously described. [36][37][38] Although these results are suggestive, whether these spherical or ellipsoidal forms are biogenic or merely abiotic mimics remains unresolved.…”

Section: Non-filamentous Cyanobacteriamentioning

confidence: 82%

Mineralized remains of morphotypes of filamentous cyanobacteria in carbonaceous meteorites

Hoover

2005

Astrobiology and Planetary Missions

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The quest for conclusive evidence of microfossils in meteorites has been elusive. Abiotic microstructures, mineral grains, and even coating artifacts may mimic unicellular bacteria, archaea and nanobacteria with simple spherical or rod morphologies (i.e., cocci, diplococci, bacilli, etc.). This is not the case for the larger and more complex microorganisms, colonies and microbial consortia and ecosystems. Microfossils of algae, cyanobacteria, and cyanobacterial and microbial mats have been recognized and described from many of the most ancient rocks on Earth. The filamentous cyanobacteria and sulphur-bacteria have very distinctive size ranges, complex and recognizable morphologies and visibly differentiated cellular microstructures. The taphonomic modes of fossilization and the life habits and processes of these microorganisms often result in distinctive chemical biosignatures associated with carbonization, silicification, calcification, phosphatization and metal-binding properties of their cell-walls, trichomes, sheaths and extracellular polymeric substances (EPS). Valid biogenicity is provided by the combination of a suite of known biogenic elements (that differ from the meteorite matrix) found in direct association with recognizable and distinct biological features and microstructures (e.g., uniseriate or multiseriate filaments, trichomes, sheaths and cells of proper size/size range); specialized cells (e.g., basal or apical cells, hormogonia, akinetes, and heterocysts); and evidence of growth characteristics (e.g., spiral filaments, robust or thin sheaths, laminated sheaths, true or false branching of trichomes, tapered or uniform filaments) and evidence of locomotion (e.g. emergent cells and trichomes, coiling hormogonia, and hollow or flattened and twisted sheaths).Since 1997 we have conducted Environmental and Field Emission Scanning Electron Microscopy (ESEM and FESEM) studies of freshly fractured interior surfaces of carbonaceous meteorites, terrestrial rocks, living, cryopreserved and fossilized extremophiles and cyanobacteria. These studies have resulted in the detection of mineralized remains of morphotypes of filamentous cyanobacteria, mats and consortia in many carbonaceous meteorites. These well-preserved and embedded microfossils are consistent with the size, morphology and ultramicrostructure of filamentous trichomic prokaryotes and degraded remains of microfibrils of cyanobacterial sheaths. EDAX elemental studies reveal that the forms in the meteorites often have highly carbonized sheaths in close association with permineralized filaments, trichomes, and microbial cells. The eextensive protocols and methodologies that have been developed to protect the samples from contamination and to distinguish recent contaminants from indigenous microfossils are described recent bio-contaminants. Ratios of critical bioelements (C:O, C:N, C:P, and C:S) reveal dramatic differences between microfossils in Earth rocks and meteorites and in the cells, filaments, trichomes, and hormogonia of recently living cyanob...

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Biomarkers and Microfossils in the Murchison, Rainbow, and Tagish Lake meteorites

Cited by 13 publications

References 0 publications

Microstructural investigation of the Carancas meteorite

Microstructural investigation of the Carancas meteorite

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

Mineralized remains of morphotypes of filamentous cyanobacteria in carbonaceous meteorites

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