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Radiometric dating

Radiometric dating (often called radioactive dating ) is a technique used to date materials such as rocks or carbon, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. [ 1 ] The use of radiometric dating was first published in 1907 by Bertram Boltwood [ 2 ] and is now the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Together with stratigraphic principles. radiometric dating methods are used in geochronology to establish the geological time scale. [ 3 ] Among the best-known techniques are radiocarbon dating. potassium-argon dating and uranium-lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts.

Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

Radioactive decay [ edit ]

Example of a radioactive decay chain from lead-212 ( 212 Pb) to lead-208 ( 208 Pb). Each parent nuclide spontaneously decays into a daughter nuclide (the decay product ) via an ? decay or a ? ? decay. The final decay product, lead-208 ( 208 Pb), is stable and can no longer undergo spontaneous radioactive decay.

All ordinary matter is made up of combinations of chemical elements. each with its own atomic number. indicating the number of protons in the atomic nucleus. Additionally, elements may exist in different isotopes. with each isotope of an element differing in the number of neutrons in the nucleus. A particular isotope of a particular element is called a nuclide. Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide. This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles ) and beta decay (electron emission, positron emission, or electron capture ). Another possibility is spontaneous fission into two or more nuclides.

For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant. It is not affected by external factors such as temperature. pressure. chemical environment, or presence of a magnetic or electric field. [ 4 ] [ 5 ] [ 6 ] The only exceptions are nuclides that decay by the process of electron capture. such as beryllium-7. strontium-85. and zirconium-89. whose decay rate may be affected by local electron density. For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time. This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present.