Stromatolites are formations of microbial mats that represent the earliest known form of life. The Archean stromatolites in the Pilbara region of Western Australia, at 3.4Ga are arguably the oldest microbial fossil record we have discovered (Strelley Pool Formation and Dresser Formation, Pilbara Craton, Western Australia).

35mm photograph
Strelley Pool Formation, 
Pilbara Craton, Western Australia

Above: Video still - site of the earliest known microbial fossil record
Below: Video still - describing similarities in the conditions now as in the formation of Earth’s early biosphere.