What is stomatolite?

Answer 1

collections of bacteria which grow in water and form stony lumps

Answer 2

Stromatolites are large, layered structures formed by the trapping and cementation of sediment by microbial mats. They are some of the oldest known fossils on Earth and provide evidence of ancient life forms and the evolution of early microbial communities. Today, stromatolites can still be found in a few locations around the world, such as Shark Bay in Australia.