Chemical nature of the 3.4 Ga Strelley Pool microfossils

Alleon, Julien; Bernard, Sylvain; Guillou, C. Le; Beyssac, Olivier; Sugitani, Kenichiro; Robert, François

doi:10.7185/geochemlet.1817

Cited by 59 publications

(66 citation statements)

References 30 publications

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“…Such incomplete specimens should be present if they were originally present in fragmented volcanic clasts. Second, the carbonaceous (Alleon et al, 2018). These results would be unexpected in volcanic vesicles and thus support the biogenicity of the described carbonaceous structures.…”

Section: What Are Lenti Cul Ar Microfoss Il S?supporting

confidence: 67%

“…To our knowledge, such morphology has never been reported for volcanic vesicles. Finally, our recent studies demonstrate a morphotype‐related variation of nitrogen isotopic ratios of the Farrel Quartzite carbonaceous microstructures (Delarue et al., ) and remarkable preservation of nitrogen‐ and oxygen‐rich organic molecules in the carbonaceous microstructures of the Strelley Pool Formation (Alleon et al., ). These results would be unexpected in volcanic vesicles and thus support the biogenicity of the described carbonaceous structures.…”

Section: What Are Lenticular Microfossils?mentioning

confidence: 84%

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Early Archean planktonic mode of life: Implications from fluid dynamics of lenticular microfossils

et al. 2018

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Lenticular, and commonly flanged, microfossils in 3.0–3.4 Ga sedimentary deposits in Western Australia and South Africa are unusually large (20–80 μm across), robust, and widespread in space and time. To gain insight into the ecology of these organisms, we performed simulations of fluid dynamics of virtual cells mimicking lenticular forms of variable sizes, oblateness, flange presence, and flange thickness. Results demonstrate that (a) the flange reduces sedimentation velocity, (b) this flange function works more effectively in larger cells, and (c) modest oblateness lowers sedimentation rate. These observations support interpretations that the lenticular microbes were planktonic—a lifestyle that could have been advantageous in an early Earth harsh environment including violent volcanic activities, repeated asteroid impacts, and relatively high UV‐radiation. Although the robustness of these organisms could have provided additional protection on the early Earth, this architecture may have impeded a planktonic lifestyle by increasing cell density. However, our data suggest that this disadvantage could have been compensated by enlargement of cell volume, which could have enhanced the ability of the flange to slow sedimentation rate, especially if coupled with vacuolation. The results of this simulation study may help to explain the unique morphology and unusually large size of these Archean microfossils.

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Section: What Are Lenti Cul Ar Microfoss Il S?supporting

confidence: 67%

Section: What Are Lenticular Microfossils?mentioning

confidence: 84%

Early Archean planktonic mode of life: Implications from fluid dynamics of lenticular microfossils

et al. 2018

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“…Fossils retain a morphological imprint of original tissues, thus providing valuable information from a past geological age ( 1 – 3 ). Organic residues present in some fossils can be found in an “exquisite” state of chemical preservation ( 4 – 6 ). In the fossil record, cellulose shows limited resilience over long periods of time.…”

mentioning

confidence: 99%

In-place molecular preservation of cellulose in 5,000-year-old archaeological textiles

Reynaud

Thoury

Dazzi

et al. 2020

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

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The understanding of fossilization mechanisms at the nanoscale remains extremely challenging despite its fundamental interest and its implications for paleontology, archaeology, geoscience, and environmental and material sciences. The mineralization mechanism by which cellulosic, keratinous, and silk tissues fossilize in the vicinity of archaeological metal artifacts offers the most exquisite preservation through a mechanism unexplored on the nanoscale. It is at the center of the vast majority of ancient textiles preserved under nonextreme conditions, known through extremely valuable fragments. Here we show the reconstruction of the nanoscale mechanism leading to the preservation of an exceptional collection of ancient cellulosic textiles recovered in the ancient Near East (4,000 to 5,000 years ago). We demonstrate that even the most mineralized fibers, which contain inorganic compounds throughout their histology, enclose preserved cellulosic remains in place. We evidence a process that combines the three steps of water transport of biocidal metal cations and soil solutes, degradation and loss of crystallinity of cellulosic polysaccharides, and silicification.

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“…Yet, diagenesis and metamorphism do not always completely obliterate the initial molecular characteristics of organic fossils. Molecular heterogeneities attributed to distinct organic precursors indeed persist despite burial temperature and pressure conditions generally considered to be incompatible with such preservation 13,36–38 . Significantly, hydrogen-, oxygen- and nitrogen-rich functional groups have been preserved in organic microfossils from chert of the Strelley Pool Formation, despite experiencing metamorphic conditions typical of prehnite-pumpellyite to lower greenschist facies, which has been assumed to be incompatible with such molecular preservation 13 .…”

Section: Introductionmentioning

confidence: 97%

“…In addition, they contain organic matter having carbon and sulfur isotopic compositions consistent with biological sources exploiting various metabolisms 4–6 . Finally, the associated sedimentary cherts host organic microstructures interpreted as microfossils based on their morphological, elemental, isotopic and molecular characteristics 7–13 . Altogether, within the framework of documented sedimentary and metamorphic histories, these observations support microbial activity in shallow-water environments on the early Earth by 3.43 Ga.…”

Section: Introductionmentioning

confidence: 99%

Organo-mineral associations in chert of the 3.5 Ga Mount Ada Basalt raise questions about the origin of organic matter in Paleoarchean hydrothermally influenced sediments

Alleon

Flannery

Ferralis

et al. 2019

Sci Rep

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Hydrothermal and metamorphic processes could have abiotically produced organo-mineral associations displaying morphological and isotopic characteristics similar to those of fossilized microorganisms in ancient rocks, thereby leaving false-positive evidence for early life in the geological record. Recent studies revealed that geologically-induced alteration processes do not always completely obliterate all molecular information about the original organic precursors of ancient microfossils. Here, we report the molecular, geochemical, and mineralogical composition of organo-mineral associations in a chert sample from the ca. 3.47 billion-year-old (Ga) Mount Ada Basalt, in the Pilbara Craton, Western Australia. Our observations indicate that the molecular characteristics of carbonaceous matter are consistent with hydrothermally altered biological organics, although significantly distinct from that of organic microfossils discovered in a chert sample from the ca. 3.43 Ga Strelley Pool Formation in the same area. Alternatively, the presence of native metal alloys in the chert, previously believed to be unstable in such hydrothermally influenced environments, indicates strongly reducing conditions that were favorable for the abiotic formation of organic matter. Drawing definitive conclusions about the origin of most Paleoarchean organo-mineral associations therefore requires further characterization of a range of natural samples together with experimental simulations to constrain the molecular composition and geological fate of hydrothermally-generated condensed organics.

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Chemical nature of the 3.4 Ga Strelley Pool microfossils

Cited by 59 publications

References 30 publications

Early Archean planktonic mode of life: Implications from fluid dynamics of lenticular microfossils

Early Archean planktonic mode of life: Implications from fluid dynamics of lenticular microfossils

In-place molecular preservation of cellulose in 5,000-year-old archaeological textiles

Organo-mineral associations in chert of the 3.5 Ga Mount Ada Basalt raise questions about the origin of organic matter in Paleoarchean hydrothermally influenced sediments

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