Life on Mars: evaluation of the evidence within Martian meteorites ALH84001, Nakhla, and Shergotty

Gibson, E. K.; McKay, D. S.; Thomas‐Keprta, Kathie L.; Wentworth, S. J.; Westall, Francès; Steele, A.; Romanek, Christopher S.; Bell, M. S.; Toporski, J.

doi:10.1016/s0301-9268(00)00122-4

Cited by 92 publications

(52 citation statements)

References 56 publications

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“…Several sets of criteria have been formulated to discriminate between abiotic and biotic structures in sedimentary rocks (Schopf and Walter 1983;Buick 1991;Gibson et al 2001). Thorseth et al 2001Thorseth et al , 2003.…”

Section: Biogenicity Of Putative Fossilized Microorganismsmentioning

confidence: 99%

Fungal colonies in open fractures of subseafloor basalt

et al. 2013

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The deep subseafloor crust is one of the few great frontiers of unknown biology on Earth and, still today, the notion of the deep biosphere is commonly based on the fossil record. Interpretation of palaeobiological information is thus central in the exploration of this hidden biosphere and, for each new discovery, criteria used to establish biogenicity are challenged and need careful consideration. In this paper networks of fossilized filamentous structures are for the first time described in open fractures of subseafloor basalts collected at the Emperor Seamounts, Pacific Ocean. These structures have been investigated with optical microscopy, environmental scanning electron microscope, energy dispersive spectrometer, X-ray powder diffraction as well as synchrotron-radiation X-ray tomographic microscopy, and interpreted as fossilized fungal mycelia. Morphological features such as hyphae, yeastlike growth and sclerotia were observed. The fossilized fungi are mineralized by montmorillonite, a process that probably began while the fungi were alive. It seems plausible that the fungi produced mucilaginous polysaccharides and/or extracellular polymeric substances that attracted minerals or clay particles, resulting in complete fossilization by montmorillonite. The findings are in agreement with previous observations of fossilized fungi in subseafloor basalts and establish fungi as regular inhabitants of such settings. They further show that fossilized microorganisms are not restricted to pore spaces filled by secondary mineralizations but can be found in open pore spaces as well. This challenges standard protocols for establishing biogenicity and calls for extra care in data interpretation.

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Section: Biogenicity Of Putative Fossilized Microorganismsmentioning

confidence: 99%

Fungal colonies in open fractures of subseafloor basalt

et al. 2013

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“…Even more important (and relevant to Mars astrobiology) is the notion that clay minerals may also provide clues that pertain to some of the geological processes that are potentially associated with biological activity (Banfield et al, 2001;Orofino et al, 2010), ultimately facilitating the search for both textural and chemical biosignatures (McKay et al, 1996Gibson et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

Chatzitheodoridis

Haigh

Lyon³

2014

Astrobiology

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A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a layer of iron oxides/hydroxides. Carbonates, halite, and sulfates were deposited last within interstitial spaces and along fractures. Among three plausible competing hypotheses here, this particular abiotic scenario is considered to be the most reasonable explanation for the formation of the ovoid structure in Nakhla, and although compelling evidence for a biotic origin is lacking, it is evident that the martian subsurface contains niche environments where life could develop.

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“…B.,25,63,108 vents. See hydrothermal vents,undersea Vernikos,Joan,205 Viewing,David,142 Viking spacecraft, 18,73,[179][180]227;biology instrument,[80][81][90][91][92][93][94][95][96][97][98][99][100][101][102]Wolf,18,[30][31][32][33][34][35]52,[57][58][59][86][87][93][94]246n13 Vogt, Steve, 172 …”

Section: The Astrobiology Institutementioning

confidence: 99%

“…Hayes, John,66,[112][113] Haymaker, Webb, 37 Holland, Heinrich ("Dick"), [48][49][109][110]Harry,204 Holton,Emily,208 Horowitz,Norman,3,25,[30][31][41][42][57][58][59][60][61]71,[83][84][85][86][87][88][89][90][91][92][93][94][95][96][97]192;and scientific skepticism,[58][59]80,[85][86][87][88] develops pyrolytic release experiment, 88ff…”

Section: Headquartersmentioning

confidence: 99%

The living universe: NASA and the development of astrobiology

2005

Choice Reviews Online

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Life on Mars: evaluation of the evidence within Martian meteorites ALH84001, Nakhla, and Shergotty

Cited by 92 publications

References 56 publications

Fungal colonies in open fractures of subseafloor basalt

Fungal colonies in open fractures of subseafloor basalt

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

The living universe: NASA and the development of astrobiology

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