Stromatolites (/stroʊˈmætəˌlaɪts, strə-/ stroh-MAT-ə-lytes, strə-) or stromatoliths (from Ancient Greek στρῶμα (strôma), GEN στρώματος (strṓmatos) 'layer, stratum' and λίθος (líthos) 'rock') are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral "microbial mats". In turn, these mats build up layer by layer, growing gradually over time.
This process generates the characteristic lamination of stromatolites, a feature that is hard to interpret, in terms of its temporal and environmental significance. Different styles of stromatolite lamination have been described, which can be studied through microscopic and mathematical methods. A stromatolite may grow to a meter or more. Fossilized stromatolites provide important records of some of the most ancient life. As of the Holocene, living forms are rare.
