Stromatolites near Wilhelmshöhe

Stromatolites (from ancient Greek στρῶμα stroma, German 'blanket' and λίθος lithos 'stone') are biogenic sedimentary rocks that are formed by the capture and binding of sediment particles or precipitation of dissolved substances as a result of the growth and metabolism of microorganisms in a body of water (biomineralization). They are usually layered and often consist of very finely layered limestone. The internal structure of the stromatolites is different: flat, even layers, upwardly curved layers, several curved layer packages next to each other (column shape). Some are reminiscent of a cauliflower with their shell-like structure of tubers, columns or wavy layers.
Source: Wikipedia

Rocks from ancient times