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The Orgueil CI1 meteorite, which fell in southern France on the evening of May 14, 1864, has been one of the most
extensively studied of all known carbonaceous meteorites. Environmental and Field Emission Scanning Electron
Microscopy (ESEM and FESEM) studies of freshly fractured interior surfaces of the Orgueil meteorite have resulted
in the detection of the fossilized remains of a large and diverse population of filamentous prokaryotic
microorganisms. The taphonomy and the modes of the preservation of these remains are diverse. Some of the
remains exhibit carbonization of a hollow sheath and in other cases the remains are permineralized with watersoluble
evaporite minerals, such as magnesium sulfate or ammonium salts. Images and EDS spectral data are
provided documenting a variety of Orgueil microstructures: abiotic evaporite minerals; pre-solar grains; framboids,
ovoids and fluorine-rich filaments of indeterminate biogenicity. These results provide information regarding the
size, size range, morphologies and chemical compositions of abiotic microstructures found in native cryptohalite and
crystalline and fibrous epsomites from Poison Lake, Washington, USA and Catalayud, Zaragoza, Aragon, Spain.
High resolution ESEM and FESEM secondary and backscattered electron Images and Energy Dispersive X-ray
Spectroscopy (EDS) data will also be presented of recognizable filamentous cyanobacteria and other prokaryotic
microfossils. Many of the microfossils found embedded in the meteorite rock matrix are consistent in size and
microstructure with known genera and species of filamentous cyanobacteria. Many of these forms can be recognized
as morphotypes of cyanobacteria belonging to the Order Oscillatoriaceae. These large, complex microstructures are
clearly distinguishable from the abiotic minerals examined - cryptohalite and fibrous epsomites. Many of the well-preserved
filamentous forms in the Orgueil meteorite are embedded in the rock matrix and exhibit identifiable
biological characteristics and EDS elemental compositions that clearly differentiate them from abiotic
microstructures. They exhibit branched and unbranched filaments; uniseriate and multiseriate ensheathed trichomes
with specialized cells and structures for reproduction (e.g. hormogonia and akinetes) and nitrogen fixation
(heterocysts). The meteorite forms also show evidence of motility (emergent hormogonia and hollow, coiled empty
sheaths) and they are often found in mats, consortia and microbial assemblages that are consistent with the known
associations and ecologies of modern genera and species of cyanobacteria. Smaller filaments, consistent with the
phototrophic filamentous prokaryotes typically present in anoxic layers associated with modern cyanobacterial mats,
have also been found in the Orgueil meteorite.
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