Black Shale (IMAGE) University of Wisconsin-Madison Caption This black shale, formed 450 million years ago, contains fossils of trilobites and other organic material that, by removing carbon from Earth's surface, helped support increases in oxygen in the atmosphere. Credit Jon Husson and Shanan Peters/UW-Madison 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.