Silica-Gel Based Chromatographic Columns (IMAGE) Proceedings of the National Academy of Sciences Caption Silica-gel based chromatographic columns show the separation of 1.1 billion-year-old bitumen from Mauritania and highlight the pink color of the geoporphyrins. Credit PNAS 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.