The geothermal gradient is the rate at which the Earth’s temperature increases with depth, typically measured in degrees Celsius per kilometer. This gradient is a critical factor in the study of geothermal energy, the formation of magmas, and the thermal evolution of the Earth’s crust. It varies widely depending on tectonic setting, crustal composition, and heat flow.
Reference: Turcotte, D. L., & Schubert, G. (2002). Geodynamics. Cambridge University Press.