Dating, in geology, archaeology, paleontology, and physics, is the determination of the actual or relative age of an object, of a natural phenomenon, or of a series of events. The most common and accepted method of absolute geologic dating (establishment of actual age) is based on the natural Radioactivity of certain minerals found in rocks; because the rate of radioactive decay of any particular Isotope is known, the age of a specimen can be computed from the ratio of the remaining isotope and its decay product. Relative geological dating (determination of the sequence of geological events) is accomplished by marking out the succession in which rocks were deposited, using various surface criteria. The identification of fossils in a geological sample is very useful, because certain assemblages of species are characteristic of specific geologic time periods. Pollen analysis, or palynology, can also establish the succession of deposits as well as the climate prevalent at the time of deposition. In archaeology and recent geology, the carbon-14 method, which measures the remaining amount of this radioactive isotope in organic matter, can date specimens as old as 35,000 years. The death of an organism terminates the previous incorporation of this isotope (created by Cosmic-Ray bombardment) at a rate equal to the isotope's known decay rate. This method's accuracy has been improved by cross-checking with dendrochronology, in which the age of a piece of ancient wood can be determined by examining the ring pattern in its cross section. The pattern of individual ring widths in a sample reflects local climatic conditions occurring at the time when the piece of wood was a growing tree. By the use of overlapping patterns found in different wood samples, dating by this method has been carried back over 8,000 years.

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