Conveners: Thomas C. (University of Geneva, Switzerland), Petráš D. (Czech Geological Survey, Czech Republic), Pérez A.M. (Institute of Palaeontology ZRC SAZU, Slovenia). Session description: From iron formations to stromatolitic facies, microbes have been instrumental for the formation, composition and preservation of sedimentary units since the dawn of life on Earth. As such, the chemical and isotopic signatures imparted by their activity in these rocks have been used to disentangle the long-term chemical evolution of the atmosphere and ancient oceans. Nonetheless, assessing the primary origin and biogenicity of certain minerals and textures remains challenging, despite these factors being crucial to our quest to understand key stages in evolution of life and earth systems. The diversity and complexity of life forms and metabolisms interacting from the moment of deposition and during shallow burial, along with the rare availability of exceptionally well-preserved ancient chemical rocks has also encouraged an active search for modern analogues to ancient microbially influenced sedimentary deposits. For this session, we seek contributions envisioning approaches for understanding the signatures derived from microbial activity on any type of sedimentary archive, including carbonates, silica-rich deposits, shales, modern lacustrine or marine sediments, soil crusts, etc. Studies describing how active microbes act as key agents in both mineral authigenesis and diagenetic alteration are particularly welcome. Given the complexity of studying such processes, the session is also open to the presentation of approaches allowing multiscale analyses, at the interface between biology and geology. Abstract submission is open until the February 15, 2020 and there are options for early career scientists to find support for coming to beautiful Prag in June via the IAS.