A giant millipede kindly provides a scale for a photo of some stromatolites in the Nama group, Namibia.
Microbial communities grow upwards towards the light. Each growth phases is cemented by carbonate grains that stick to the sticky EPS substance that the communities produce, forming layered stromatolite columns. The stromatolites pictured above formed 550 million years ago – just as some of the first shelly organisms were emerging.
(c) Geology for Global Development 2013