"Humans have become a geologic agent comparable to erosion and [volcanic] eruptions ..." Paul J. Crutzen, a Nobel Prize-winning atmospheric chemist. Using Landsat imagery, scholars create a grid showing land use type, such as urban, rural, river, etc. Then, they draw another land use grid for the same area using data from a decade later. The comparison of the two grids shows how humans have altered the environment. Lesson focuses on the impact humans have on the climate in the seventh lesson in a series of 21.