Fossilized Tracks (IMAGE) University of Alberta Caption This sample of black shale contains string-like fossilized tracks that may have been left behind by multicellular organisms 2.1 billion years ago. (Photo courtesy of courtesy of Abder El Albani) Credit Abder El Albani Usage Restrictions with credit to Abder El Albani 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.