Mark van Zuilen

Abstract of the talk: In the most ancient rocks on Earth traces of life are controversial, either because they partially broke down due to diagenesis, hydrothermal alteration, and metamorphism, or because there were abiologic processes that generated similar ‘non-living’ forms of complexity. Here I present a recent study on silicification of filamentous cyanobacteria in a modern hot spring silica sinter, showing how early diagenesis affects the degradation of cell membranes, sheaths, and extracellular polymeric substances. Experimental work at elevated temperatures and pressures further shows how the silica matrix recrystallizes and generates complex abiologic fabrics. In addition, I show how under certain silica-rich, alkaline aquatic conditions abiologic self-assembled mineral aggregates can form, that mimic microfossil morphologies. An assessment is made of the methods and analytical tools for finding traces of life in ancient silica deposits.