Harold ("Hal") Levin began his career as a petroleum geologist in 1956 after receiving bachelor's and master's degrees from the University of Missouri and a doctorate from Washington University. His fondness for teaching brought him  back to Washington University in 1962, where he is currently professor of geology and paleontology in  the Department of Earth and Planetary Sciences. His writing efforts include authorship of seven edition of The Earth Through Time, four editions of Contemporary Physical Geology; Essentials of Earth Science and co-authorship of Earth: Past and Present, as well as eight editions of Laboratory Studies in Historical Geology; Life Through Time, and more recently, Ancient Invertebrates and Their Living Relatives.   For his courses in physical geology, historical geology, paleontology, sedimentology, and stratigraphy, Hal has received several awards for excellence in teaching. The accompanying photograph was taken during a lecture on life of the Cenozoic Era. The horse skull serves to illustrate changes in the teeth and jaws of grazing animals in response to the spread of prairies and savannahs during the Miocene and subsequent epochs.