Basalt Layers (IMAGE) University of California - Riverside Caption Layered volcanic rocks in Eastern Greenland that are up to 4 miles thick were formed during ancient volcanic eruptions that caused a global warming event called the Palaeocene-Eocene Thermal Maximum (PETM). Credit Michael Storey, Natural History Museum of Denmark 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.