Formation of Crystalline Silica-Carbonate Biomorphs of Alkaline Earth Metals (Ca, Ba, Sr) from Ambient to Low Temperatures: Chemical Implications during the Primitive Earth's Life

The Earth has undergone at least four great glaciations, during which the ice layers and the glaciers have expanded all over the planet, corresponding to significant drops in global temperatures that lasted millions of years. Since the Precambrian era, ice ages have occurred at intervals of several millions of years. It is considered that the impact on the biosphere was large, because life was on the brink of disappearing completely from the planet. During these glaciation periods, carbon was reassigned, with the subsequent formation of carbonates called cap carbonates, which present stromatolite-like activity. These findings prove that life was conserved even during the glacial period. Knowledge on life conservation during the glacial period through stromatolites that have endured until the present day, is of special relevance. In recent investigations, in vitro structures have been synthesized; these crystalline aggregates have been named biomorphs because they mirror the morphologies of primitive organisms called Precambrian cherts. These biomorphs have been synthesized at different temperatures (from room temperature to lower ones). The aim of the present work was to synthesize CaCO₃, BaCO₃, and SrCO₃ silica-carbonate biomorphs at three low temperatures (4 °C, -20 °C, and -70 °C). CaCO₃ biomorphs present almost the same morphology at all temperatures with a calcite crystalline structure, whereas BaCO₃ and SrCO₃ biomorphs present remarkably different morphologies depending on temperature with witherite and strontianite crystalline structure, respectively.