Lecture 3: Biomineralogical study of stromatolites at the nanoscale
Stromatolites are layered sedimentary structures initiated from a limited surface and forming a variety of morphologies. They are often composed of calcium carbonates and found throughout the geological record back to 3.5 Ga. While they have often been considered as one of the oldest traces of life on Earth, the relative impact of abiotic and biological processes involved in the formation of modern stromatolites is yet poorly known. We believe that a detailed study of mineralogical processes occurring in modern stromatolites would dramatically improve our understanding of ancient samples. In this talk, I will present some of our recent work on Archean stromatolites (from the Tumbiana Formation, Australia, 2.7 Gyr) and modern stromatolites from hyperalkaline lakes. I will discuss the origin of laminations in lake stromatolites; I will show how the combination of 
microscopy and spectroscopy techniques, including transmission electron microscopy and synchrotron-based x-ray microscopy allow evidencing diverse pools of organic matter in modern and ancient stromatolites. Finally, I will show a preliminary study of the crystallographic texture of minerals in modern stromatolites. Altogether, this information will help discussing existing models for the formation of stromatolites and the way we interpret the geological record.
