Stromatolite from the Precambrian of Australia. (Cranbrook Institute of Science collection, Bloomfield Hills, Michigan, USA)

This is a sample from the oldest known definite fossil occurrence on Planet Earth. This is a stromatolite from the Paleoarchean of Western Australia.

Stromatolites are large, layered structures built up by mats of cyanobacteria. They vary in appearance, ranging from slightly wrinkled horizontal laminations in sedimentary rocks to low mounds to prominent mounds to columnar structures and other forms. Stromatolites are most common in the Proterozoic fossil record. They are scarce today, but famous modern examples occur at Shark Bay, Western Australia. The oldest known examples are ~3.5 billion years old, from Western Australia - this is a specimen from that occurrence.

Stratigraphy: stromatolitic-chert member, Strelley Pool Formation, middle to lower Paleoarchean, 3.35 to 3.46 Ga