1,721,213 research outputs found
La ricerca della vita nell’Universo
No full textEsiste vita altrove nell’Universo? Questa domanda trascende una singola cultura o epoca e accompagna la nostra specie da millenni, ma solo negli ultimi decenni è stato possibile cominciare a cercare risposte nei dati raccolti da strumenti sempre più sensibili e sofisticati
Microbial survival and adaptation in extreme terrestrial environments – the case of the Dallol geothermal area in Ethiopia
No full textIn the quest to find life on other planets, specific extreme terrestrial environments are studied as analogues to present or past conditions on other bodies of our Solar System and beyond. These terrestrial extreme environments often harbour microbial life of high diversity and abundance. These microbes, mostly Bacteria and Archaea, develop survival and adaptation strategies enabling them to withstand harsh conditions. The physico-chemical boundaries for life on Earth are very broad and extreme environments on Earth are highly diversified. Extreme Earth ecosystems bear similarities to past or present environments on planets such as Mars and Venus but may also be analogues to certain moons of gas giants, such as Titan, Europa, and Enceladus.
In this review we (1) report the recently described planetary field analogue environment from the Dallol geothermal area in the Danakil Depression, Ethiopia, in which polyextremophilic physical and chemical boundaries for life on Earth coexist; and (2) summarise the physicochemical conditions of extreme terrestrial environments in comparison to extra-terrestrial examples within the framework of our knowledge of microbial life and its adaptation to extremity, suggesting whether and how life could adapt to present or past potential extra-terrestrial habitats. We also explore the distribution and geographical dispersal of microorganisms that inhabit these terrestrial ecosystems and discuss implications for Panspermia
Early taphonomic processes in a microbial-based sedimentary system from a temperate salt-pan site (Cervia salterns, Italy)
Full text linkIn the only salt evaporation pond retaining its natural setting of the historic Salina di Cervia (Italy), the northernmost salterns of the Mediterranean area, a number of potentially preservable textures derive from the interactions between photosynthetic mat producers and the sedimentary substrate. These morphologies occur at the beginning of the taphonomic processes when repeated emerged-submerged conditions take place. In these conditions the cohesive nature of the diatom- and cyanobacterial-derived mucilage favours the stabilization of otherwise ephemera structures. Surface micromorphologies for which diatoms and cyanobacteria have played some active role when still living in the soft microlayer and down to the sediment-water interface, such as during the gliding motility, can overcome the surface layer of most intense mixing (i.e., the taphonomically active zone) and keep traces of them in the fossil record either as body fossils or as texture contributors. Tiny microbial-derived remnants, such as filaments and biofilm strands of halotolerant microorganisms, while fragile upon their formation, can therefore stabilize as biosignatures when combined with salt precipitation. Halophilic and halotolerant ecosystems are models for life in extreme environments (analogue sites) with similarity to those strongly suspected to occur and/or have occurred on Mars and on other planetary bodies. The study of hypersaline systems such as Salina di Cervia which harbour diverse and abundant microbial life, can be relevant for astrobiology since it allows the investigation of potential biosignatures and their preservation, and of further understand the range of conditions and the planetary processes sustaining potentially habitable systems
Microbial geomorphologies in modern salt flats and their astrobiological significance
No full textFollowing the discovery of Martian mineral deposits with an assumed evaporite origin (especially sulfates), salt flat areas from hot and cold arid environments (such as sabkhas and playa lakes) are currently investigated for comparative analysis between terrestrial salt-bearing settings and their Martian environmental analogs. Similarly to the Earth, evaporite deposits seem widespread on Mars where their stratigraphic setting and composition suggest relationships with aqueous environments and, therefore, they represent a useful indicator of habitability.
Among the traces of biological activity retained in salt flat settings those produced by surface to near surface microbial activity deserve a special astrobiological interest. These microbial geomorphologies derive from the interaction between physical and biological agents, and can impact on the development and stabilization of surface morphologies with some fossilization potential. Therefore, once established a clear relationship between micro-geomorphologies and micro-biota, their recognition at the surface on Martian terrains may represent unambiguous indicators of biogenicity.
In the sabkha Oum Dba, near the Atlantic coast of the Western Sahara (southern Morocco), thick microbial mats and mineral precipitations (carbonates and sulfates) are in progress and actively interact in an ecosystem where living and fossilized sectors coexist. It, therefore, represents an ideal natural site for detecting type, evolution, and stabilization of microbial geomorphologies in a typical arid salt flat area
Mineralogical characterization of apatite biominerals: preliminary results
No full textBioapatite fossils are investigated and compared by the use of microdiffraction technique
Biosignatures for Astrobiology
No full textThis book aims at providing a brief but broad overview of biosignatures. The topics addressed range from prebiotic signatures in extraterrestrial materials to the signatures characterising extant life as well as fossilised life, biosignatures related to space, and space flight instrumentation to detect biosignatures either in situ or from orbit. The book ends with philosophical reflections on the implications of life elsewhere. In the 15 chapters written by an interdisciplinary team of experts, it provides both detailed explanations on the nature of biosignatures as well as useful case studies showing how they are used and identified in ancient rocks, for example. One case study addresses the controversial finding of traces of fossil life in a meteorite from Mars. The book will be of interest not only to astrobiologists but also to terrestrial paleontologists as well as any reader interested in the prospects of finding a second example of life on another planet
Compositional data analysis and hydrogeochemistry of the Continental Intercalaire aquifer (northwestern Africa): A regional synthesis
No full textThe Continental Intercalaire (CI) aquifer, spanning Algeria, Tunisia, and Libya, is analyzed using piezometry, major ions, and stable isotopes (δ2H, δ18O) to track flow paths from recharge to discharge areas. A new piezometric map was generated for the CI from the interpolation of extensive datasets from the three countries (measured in 2008). A hydrochemical study was conducted on data compiled from previous investigations (n = 248 samples) and compared to new samples from this study (n = 10 samples). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were applied to hydrochemical data transformed using the centered log ratio method. The piezometric map, created using a nested model (spherical and gaussian variograms), achieved high accuracy (MAE = 0.09 m; RMSE = 26.62 m). Variography revealed the lateral continuity of the CI aquifer over ~600 km, in agreement with previous studies on flow paths and recharge characteristics. Depth to groundwater is shallowest in coastal areas (~20 m) and deepest in the Sahara (440 m). The hydrochemistry data shows that there is a progression towards the NaCl-SO4 water type along flow paths. Compositional data analysis (CoDA) successfully differentiates similar water types, providing additional insights into CI aquifer geochemistry. Isotopes proved essential in interpreting both paleo-recharge and modern-recharge compositions, considering depletion and enrichment in δ2H and δ18O compared to the global meteoric water line (GMWL) and the palaeo water line (PWL). These results are vital for sustainable water management and environmental planning
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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