Stromatolities, living example of Earth's earliest fossils from billions of years ago, near Port Lincoln

Stromatolites living on Sleaford Mere, a saline lake near Port Lincoln.
Image by Evelyn Leckie, courtesy ABC Eyre Peninsula

Sleaford Mere, a saline lake near Port Lincoln on South Australia’s Eyre Peninsula, is one of the few places where stromatolites exist as Earth’s oldest living fossils.

Also found as living fossils in Shark Bay, Western Australia, stromatolites are microbial reefs that have been forming from about 3.5 billion years ago. They are built by tiny organisms or cyanobacteria trapping sediment and excreting calcium carbonate.

They have been of particular interest to experts such as Flinders University palaeontologist Aaron Camens as the first evidence of life on Earth and the start of evolutionary change. Stromatolites created an atmosphere allowing  enough oxygen to support life.

Although extremely vulnerable to being grazed by other animals, the stromatolites near Port Lincoln were protected by brackish Sleaford Mere and separated from the Southern Ocean by porous sandstone. But Dr Camens told ABC (Australian Broadcasting Corporation) news on Eyre Peninsula in 2020 that, alternatively, rising sea levels could threaten the future survival of the Sleaford Mere stromatolites.

South Australia also has dead fossil evidence of stromatolites in the Flinders Ranges and its southeast region. The Flinders Ranges are already became famous for its imprints of ediacaran fossils from 570 million to 540 million years ago, but carbonate rock in the northern ranges have stromatolite structures believed to have formed from bacteria present during the Cryogenian era, about 50 to 70 million years earlier than the ediacaran tubular and frond-shaped fossils.

Stromatolites composed of calcite have been found in both in the dormant volcano of the Blue Lake at Mount Gambier and in at least eight cenote lakes including the Little Blue Lake in the lower southeast region of South Australia. Ancient stromatolites finds in South Australia have been divided into categories such as Skillogalee dolomite and the Umberatana group.