Thure Cerling, a University of Utah professor of both geology and biology, and a pioneer in the use of isotope analysis, shares how geologists have developed a method for tracking the movements of large herbivores across landscapes, even for animals now extinct, such as mastodons and mammoths. Then, Ben Stanger discusses the history, science and wonder of the cell in his book "From One Cell: A Journey into Life’s Origins and the Future of Medicine."