Over the course of Earth's history, the crust has been repeatedly formed, deformed, deconstructed (weathered and eroded), and renewed by physical and chemical processes. Observations at many scales, together with physical and chemical analyses, allow us to understand these processes. Research within the department in petrology, geochemistry, geophysics, and structural geology is leading to new discoveries about how physical and chemical processes affect the Earth's crust. Concepts of plate tectonics — the paradigm that the outermost portion of the Earth is separated by giant fracture systems into stiff mobile plates — provide a unifying framework for our research.