This week, we're looking across the Periodic Table and assessing the scarcity of modern society's essential elements. We're joined by Dr. Thomas Graedel, Director of the Center for Industrial Ecology at Yale University, to talk about the rare metals that play a role in our electronic devices. We'll speak to physics Professor Dr. Moses Hung-Wai Chan about our dwindling supply of helium. And we'll talk about the phosphorous that plays a critical role in modern agriculture, with ecology professor Dr. James Elser, co-organizer of the Sustainable Phosphorus Initiative at Arizona State University.