Stromatolites exist in only a few places on earth, and are formed by the trapping, binding, and cementing of sedimentary grains by microscopic bacteria (or microbes). These ‘living rocks’, as they are sometimes called, teem with the very oldest life forms on earth, having remained virtually unchanged during the comings and goings of animals and plants.

This is an accessible, illustrated account of the structure and formation of these ancient constructions, which have been on Earth for nearly 3.5 billion years.