An Outcrop of Carbonate Stromatolites (IMAGE) Proceedings of the National Academy of Sciences Caption An outcrop of carbonate stromatolites. Features such as these were used to estimate the original water depths of samples collected for analysis. Credit <i>PNAS</i> 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.