Lecture, three hours; discussion, one hour. Designed for graduate physical or biological sciences students. Theoretical basis and application of thermochronometry: derivation of diffusion equation and methods of solution, relationship between heat and mass diffusion and their simultaneous solution, Boltzmann/Matano analysis, multicomponent diffusion, closure theory; 40Ar/39Ar systematics and interpretive models, multidiffusion domain theory, petrological applications. Letter grading.