Much of Earth history is recorded in the beds of sedimentary rocks, which are read from bottom to top. Professor Heckel started with his PhD on a Devonian limestone that forms waterfalls in Upstate New York. Since then, his work at the Kansas Geological Survey, followed by his career at the University of Iowa with his students, has involved repetitive successions of Pennsylvanian limestones, shales and sandstones (called cyclothems) from Iowa to Oklahoma, and in Illinois, Ohio and Pennsylvania. He has also visited Pennsylvanian successions in Spain, Russia, Ukraine, and China. Geologists often see some humorous things while working in the field.