Geochemistry embraces all aspects of the study of the Earth. In this course, we will look at the formation of our home planet, in the age before geologic time began. We will investigate the reasons why it is chemically zoned, with a molten core, hot rocky mantle, chilled outer crust, watery ocean, and turbulent gaseous atmosphere. We will look at specific aspects of the Earth's chemical systems, including the chemical clocks that give us the ages of rocks; the nature of weathering, and the formation of soils; chemical thermometers and barometers that provide information about temperatures and pressures within the Earth; and isotopic data from fossils and ice that provide a record of ocean temperatures and climate in the geologic past. We will also examine processes operating in the earth system at the present time, including the formation and destruction of stratospheric ozone, the origin and remediation of acid mine drainage, and other environmental issues. Lectures, three hours per week. One all-day field trip. Evaluation will be based on problem sets, critical discussions, one hour exam, and a final exam. Prerequisite: one 100-level Geosciences course or permission of instructor.