In geology, archaeology, paleontology, and physics, 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 Rays 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.