Professor Marshak has been a faculty member in the Department of Geology for 35 years, and became full-time in 2018. He served as Head of the Department of Geology for 8 years, and then as Director of the College of Earth, Society and Environment for 10 years. In addition to research in structural and tectonic geology, he maintains a keen interest in earth science education. He has authored or authored university textbooks in introductory geology, earth sciences, and structural geology, most of which have been published by W. Norton & Company. He has also developed a MOOC (Open Online Course) which is offered through Coursera.