Size evolution of micropyrite from diagenesis to low-grade metamorphism

Size distribution and evolution of framboidal and euhedral microscopic crystals of pyrite (micropyrites, MPy) have been used for the last thirty years to deduce palaeo-redox conditions. The analysis of the MPy distributions can give valuable information about these palaeo-redox conditions. However, other information can also be retrieved from this type of analysis. In this work, we propose that the formation of new populations of MPy is a proxy of the transition from the anchizone to the epizone. High-resolution X-ray tomography (micro-CT) was used to determine the size distributions of MPy hosted in pelitic rocks subjected to different grades of low temperature metamorphism. These data were filtered and statistically analysed, which allowed us to find a statistical representative size distribution of the MPy present in the samples. The metamorphic grade was determined using the Kübler Index in combination with petrological and scanning electron microscopy (SEM) examination. The results show a relationship between metamorphic grade and MPy size distributions, and that new populations of MPy formed due to the effects of metamorphism. This new methodology for MPy size distribution has different potential applications in some fields of Earth sciences, such as palaeoenvironment reconstruction, ore mining or metamorphic petrology

Size evolution of Micropyrite from Diagenesis to low-grade metamorphism

Size distribution and evolution of framboidal and euhedral microscopic crystals of pyrite (micropyrites, MPy) have been used for the last thirty years to deduce palaeo-redox conditions. The analysis of the MPy distributions can give valuable information about these palaeo-redox conditions. However, other information can also be retrieved from this type of analysis. In this work, we propose that the formation of new populations of MPy is a proxy of the transition from the anchizone to the epizone. High-resolution X-ray tomography (micro-CT) was used to determine the size distributions of MPy hosted in pelitic rocks subjected to different grades of low temperature metamorphism. These data were filtered and statistically analysed, which allowed us to find a statistical representative size distribution of the MPy present in the samples. The metamorphic grade was determined using the Kübler Index in combination with petrological and scanning electron microscopy (SEM) examination. The results show a relationship between metamorphic grade and MPy size distributions, and that new populations of MPy formed due to the effects of metamorphism. This new methodology for MPy size distribution has different potential applications in some fields of Earth sciences, such as palaeoenvironment reconstruction, ore mining or metamorphic petrology

Astrobiology and the possibility of life on Earth and elsewhere…

Astrobiology is an interdisciplinary scientific field not only focused on the search of extraterrestrial life, but also on deciphering the key environmental parameters that have enabled the emergence of life on Earth. Understanding these physical and chemical parameters is fundamental knowledge necessary not only for discovering life or signs of life on other planets, but also for understanding our own terrestrial environment. Therefore, astrobiology pushes us to combine different perspectives such as the conditions on the primitive Earth, the physicochemical limits of life, exploration of habitable environments in the Solar System, and the search for signatures of life in exoplanets. Chemists, biologists, geologists, planetologists and astrophysicists are contributing extensively to this interdisciplinary research field. From 2011 to 2014, the European Space Agency (ESA) had the initiative to gather a Topical Team of interdisciplinary scientists focused on astrobiology to review the profound transformations in the field that have occurred since the beginning of the new century. The present paper is an interdisciplinary review of current research in astrobiology, covering the major advances and main outlooks in the field. The following subjects will be reviewed and most recent discoveries will be highlighted: the new understanding of planetary system formation including the specificity of the Earth among the diversity of planets, the origin of water on Earth and its unique combined properties among solvents for the emergence of life, the idea that the Earth could have been habitable during the Hadean Era, the inventory of endogenous and exogenous sources of organic matter and new concepts about how chemistry could evolve towards biological molecules and biological systems. In addition, many new findings show the remarkable potential life has for adaptation and survival in extreme environments. All those results from different fields of science are guiding our perspectives and strategies to look for life in other Solar System objects as well as beyond, in extrasolar worlds