NANOCRYSTALS AS BIOSIGNATURES IN 3.5 BILLION YEARS OLD MICROBIAL REMAINS

Natural, spherical aggregates of carbonaceous materials (CM), called clots (average diameter: ca. 200 microns), embedded in ancient chert (silica) host matrix represent the most common type of the ancient CM with purported biological origin on Earth. However, to date they have received scarcity of attention and are only been qualitatively described. The clots object of this study, have the same age of the oldest know fossils know. The aim of the proposed research project is to characterize at the micro-nano-atomic-scale, the different generation of natural, spherical aggregation of carbonaceous materials that can be recognized from ca. 3.5-3.3 billion years old rocks from Barberton greenstone belt in South Africa, to demonstrate their biological (or abiotic?) origin, and, possibly, deciphering crucial aspects of early life. Mineral nano-phases, trace elements and molecular information can be used as biological signals when associated to morphological features coming from the right geological context. Therefore, versatile in situ analytical techniques borrowed from nanotechnology become of critical importance as they can provide morphological, structural, chemical, and mineralogical signatures to recognize abiotic microfossil-like structures, identify fossil microorganisms, demonstrate their antiquity, and decipher their activities and host environments. The complete characterization of the CM of the clotted textures will be crucial to explore their role in Archaean (4-2.5 billion years) geochemical and biogeochemical processes, since they represent an important and unknown fraction of the ancient carbonaceous materials. This represent a novel, interdisciplinary study (across geobiology, nanotechnology and material sciences) as investigates a type of ancient CM, that has so far not been subjected to any detailed geo-biological researches, but that can be demonstrated to be associated to life.