n.
In geology and archaeology, the process of determining an object's or event's place within a chronological scheme.
Scientists may use either relative dating, in which items are sequenced on the basis of stratigraphic clues (see stratigraphy ) or a presumed evolution in form or structure, or absolute dating, in which items are assigned a date independent of context. The latter type includes potassium-argon and carbon-14 dating; both are based on the measurement of radioactive decay. The record of changes in polarity of the Earth's magnetic field has provided a timescale for seafloor spreading and long-term marine sedimentation . Dendrochronology has proved useful in archaeology and climatology. See also fission-track dating ; helium dating ; lead-210 dating ; rubidium-strontium dating ; uranium-234uranium-238 dating ; uranium-thorium-lead dating .