Self-organized colloidal growth of stromatolites

Abstract Stromatolites have been widely regarded as key biosignatures of early life, yet the controls on their morphogenesis and diversity remain poorly constrained. Here, we investigate Mesoproterozoic ironstones from North China featuring stromatolitic structures and composed of laminated Fe(III)-oxyhydroxide colloids. Microstructural observations and colloidal stability calculations indicate that terrestrial colloids flocculated rapidly upon mixing with seawater in an estuarine environment and aggregated on the seafloor. We then numerically simulate the forming processes of stromatolites via diffusion-limited aggregation and surface diffusion (DLA–SD) mechanism and reveal that stromatolitic morphogenesis is primarily controlled by depositional and aggregation dynamics of colloids, which are related to geochemical and hydrodynamic conditions in estuaries. This DLA–SD framework also provides quantitative insights into the microbial sediment-trapping mechanisms for the formation of carbonate stromatolites and reveals that the diversification of morphologies of stromatolite were linked to the evolution of oceanic chemistry and microbial communities throughout the Earth history.