This course will examine how the chemistry of the Earth System has changed through geologic time including recent perturbations by humans. The scientific principles of thermodynamics (i.e., Gibbs free energy), redox chemistry, acid-base chemistry and kinetics will be used throughout the course to understand the observed changes. The first half of the course will focus on the natural biogeochemistry of the Earth and how the chemistry of the Earth has changed through time highlighting both the basic chemistry and the geological evidence. Within this scientific context, students will understand that the chemistry of the Earth System has changed dramatically due to both biological and abiotic forcings and that change is normal. The second half of the course will discuss the effects of recent human perturbations to the chemistry of the Earth, with a focus on atmospheric chemistry and some of the major processes involved.