Stromatolite from Fife, Scotland, UK (REF:SS15)

Fossil Stromatolites are among the oldest evidence for life on Earth with some fossils dating back as far as 3.5 billion years old. 

Stromatolites are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulphate-cyanobacteria, sulphate-reducing bacteria, and Pseudomonadota. 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.

Possibly without Stromatolites, life on Earth wouldn’t be what it is today. These early life forms release of oxygen actually aided the development of more complex life on Earth 

Shark Bay in Australia is one of the few localities worldwide where living, growing stromatolites can be seen today.