These images are of a 900 million year old stromatolite fossil from Atar rock formation of Mauritania, Africa. This fossil is from the low oxygen atmosphere Precambrian Period. Stromatolites are mats of aerobic cyanobacteria and anaerobic bacteria that grew under shallow water. It is thought that since an ozone layer had yet to form around the Earth at this time in history that water protected life from intense ultraviolet light but allowed energy from other wavelengths allowing growth.
The mats of bacteria formed colonies that stacked overtime to form columns with grey carbonate mud in between branches. The specimen was cross cut and polished to allow better viewing of layers. Second picture is of the outer surface of specimen.
Fossil on display at American Museum of Natural History, New York City, USA as of July 2018.