1,720,982 research outputs found
Microfacies characterization of stromatolites from Lake Ashenge in the East African Rift System
No full textCarbonate–silica interplay: unraveling microbial synergy and fossil preservation in alkaline lacustrine stromatolites
No full textControls on Preservation of Stromatolites from Extreme Alkaline Environments (Lake Ashenge, Tigray, Ethiopia)
No full textStromatolites from extreme environment as tools for astrobiological exploration, study case of Lake Ashenge, East African Rift system
No full textStromatolites are ideal ecosystems of microbe–sediment synergy and, therefore, represent a fundamental resource for the recognition of biosignatures and investigation of astrobiological targets with regard to environment and life interactions. Even though they are one of the oldest records of life on Earth, at present, modern occurrences of stromatolites are restricted to extreme environments, such as hypersaline lakes. This work aims to characterize stromatolite features that can be used as biosignatures, seeking to understand their morphogenetic and preservation processes. Samples were collected in Lake Ashenge, a hyperalkaline high-altitude lake located in the Tigray Region of Ethiopia.
Two distinct microfacies were observed in the Lake Ashenge stromatolites: a) columnar stromatolites; and b) bulbous stromatolites. Both microfacies feature of slightly laminated microfabric composed of intercalated thicker layers of microsparite and thinner layers of calcite micrite within which exceptionally well-preserved microbial fossils including filamentous and coccoidal cyanobacteria-dominated colonies were recognized. Columnar stromatolite layers show mostly parallel or interlaced vertical arrangements of filamentous microbes which suggest different directions of water flow, demonstrating that the spatial arrangements of microbes reflect the dynamics of the environment. Bulbous structures are composed either of colonies of shrub-like filaments along their entire length and height grading into a vertical parallel arrangement at the top. This type of arrangement suggests self-sustainability of the microbial community, improving the resistance of the structures, in order to endure physical processes in the environment such as currents and wave action or predation. All samples show extracellular polymeric substances (EPS) produced by microbes normally associated with filamentous microbes. In this context, EPS may serve to support and stabilise the biofilm and contribute to the formation of columnar and bulbous structures.
Mars 2020 Perseverance rover recorded carbonate occurrences in Martian paleoenvironments from Jezero Crater which have been compared with microbialites and tufas with the potential to preserve biosignatures similar to those found in Lake Ashenge samples. Therefore, although stromatolite morphology itself configures a macroscopic biosignature which may be detected in Mars rover images, the two scales of observation (millimetres- centimetres vs micrometric) identified biosignatures in the stromatolites of Lake Ashenge could also reflect different conditions of the dynamic environment during their development. In this regard, Lake Ashenge illustrates an important modern environment for astrobiological studies and has potential analogy to ancient lacustrine environments on Mars
Decoding the biogeochemical landscape of early life on Earth
No full textConvincing traces of life – biosignatures – have been studied back to approximately 3.5 Ga, suggesting that microbial communities were already sophisticated in their metabolic machinery and distributed through multiple environmental settings. Furthermore, biocoenosis-level ecosystem complexity had evidently already been achieved by 3.5 Ga. Recent evidence from Palaeoarchaean to Neoarchaean (~3.6-2.5 Ga) rocks has further shed light on the co-evolution of Earth and Life: microbial diversity increases together with geological and environmental diversity, with substantial diversification at moments of global environmental revolution such as the development of widespread continental masses or the Great Oxygenation Event. This system of positive feedbacks is reminiscent of the Gaia
Hypothesis
Fossilization of Bacteria and Implications for the Search for Early Life on Earth and Astrobiology Missions to Mars
No full text3.4 Ga biostructures from the Barberton greenstone belt of South Africa: new insights into microbial life
No full textRaman spectroscopy is a molecule-specific technique allowing the investigation of the chemical structure of organic and inorganic geological materials. Since this is a non-destructive and relatively non-invasive analytical procedure, Raman spectroscopy is ideally suited to palaeontology. Raman spectroscopy is herein applied to the study of carbonaceous chert facies of the ~3.4 Ga old Buck Reef Chert of South Africa, which contain some of the oldest well-preserved evidence of early life. Laminated chert typically consists of microbands composed of microcrystalline quartz (chert) and an association of siderite and carbonaceous material (CM) in the form of mat-like laminations, simple carbonaceous grains, vein infills and diffuse CM. Using Raman spectroscopy the structural characteristics of CM in mat-rich chert have been investigated and compared with grains of CM from the same unit, but wich were deposited as massive layers that bear no evidence of microbial influence. All CM retains a structural organisation consistent with a lower greenschist grade regional metamorphic imprint, however, this detailed study of the CM Raman signals revealed some heterogeneity between the different sedimentary facies, thus pointing to the presence of different CM types. Different CM precursors are indicated and may reflect either different CM sources or different alteration chemistries from various microbial metabolic pathways
Supplemental Material: Advanced two- and three-dimensional insights into Earth’s oldest stromatolites (ca. 3.5 Ga): Prospects for the search for life on Mars
No full textMethods, Figures S1–S16, and Table S1. </p
Traces of early Life from the Barberton Greenstone Belt, South Africa
No full textWe review the evidence for traces of Paleoarchean (3.47–3.2 Ga) life in the Barberton Greenstone Belt (BGB), South Africa. Morphological, organic, geochemical, isotopic, and mineralogical biosignatures are preserved in massive and stratiform volcano-sedimentary cherts, in hydrothermal and chemical sedimentary rocks, and in quartz-rich sandstones. The well-preserved lithologies of the BGB record a broad diversity of features interpreted as the remnants of anaerobic life forms, including chemotrophs, benthic phototrophs, and possible planktonic organisms. Inferred photosynthetic fossils include planar to low-amplitude, finely laminated microbial mats and stromatolites from marine and terrestrial settings. Rarely preserved, putative, filamentous microfossils are very small compared with present-day phototrophs. Putative chemotrophic fossils are more enigmatic and generally restricted to nutrient-rich hydrothermal environments. Relatively large (up to some hundreds of microns) lenticular and spherical carbonaceous microfossils are interpreted as possible planktonic forms. Many proposed microfossils are of simple morphology and poorly preserved, thus it is difficult to completely discount abiogenic mechanisms for their formation
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