Stromatolites (IMAGE) Princeton University Caption These layered structures called stromatolites from the Cryogenian Trezona Formation were created by biofilms of microbes that formed in a shallow-water tropical environment in South Australia's Adelaide Rift Complex about 650 million years ago. Credit Nicholas Swanson-Hysell Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.