Did you ever wonder where the concrete in a sidewalk, the asphalt in a highway, the brick in a building, or the glass in a window come from? All are derivatives of rocks and sediments, processed in ways that allow the cities of modern society to exist. But use of these materials comes at a cost to the environment, and supplies of some are not sustainable. Prof. Emeritus Stephen Marshak was on the faculty at the University of Illinois for 35 years. He has served as Geology Department Head and as School of Earth, Society & Environment Director.