Figure 1 (IMAGE) Tohoku University Caption A massive outcrop of stromatolitic chert from the Gunflint Formation. Credit Sasaki et al. Usage Restrictions Reporters may use freely these materials in news coverage with appropriate credit information. License Original 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.