# Potassium argon dating in archaeology

## Potassium-argon dating

The process by which an archaeologist determines dates for objects, deposits, buildings, etc. Relative datingin which the order of certain events is determined, must be distinguished from absolute datingin which figures in solar years often with some necessary margin of error can be applied to a particular event. Unless tied to historical records, dating by archaeological methods can only be relative -- such as stratigraphy, typology, cross-datingand sequence dating.

Absolute datingwith some achaeology, is provided by dendrochronology, varve datingthermoluminescence, potassium-argon datingand, most important presently, radiocarbon dating. Some relative dating can be calibrated by these or by historical methods to give a close approximation to absolute dates -- archaeomagnetism, obsidian hydration datingand pollen analysis. Still others remain strictly relative -- collagen contentfluorine and nitrogen test, and radiometric assay.

The methods have varying applications, accuracy, range, and cost. Many new techniques are being developed and tested. The basis for this technique is that a uranium isotope, Potassium argon dating in archaeologyas well as decaying to a stable potassjum isotope, also undergoes spontaneous fission. One in every two million atoms decays in this way. Fission is accompanied by an energy release which sends the pltassium two nuclei into the surrounding material, the tracks causing damage to the crystal lattice.

These tracks can be counted under a microscope after the polished surface of the sample has been etched with acid. The concentration of uranium can be determined by the induced fission of U by neutron irradiation of the sample. Since the ratio of U to U is known, and is constant, a comparison of the number of tracks from natural fission and the number from induced fission will give the age of the sample.

Though the method has been limited in its archaeological use so far, it has already proved a useful check method for potassium-argon dating for volcanic deposits at Olduvai Gorge, Tanzania, and obsidian, tephra beds, mineral inclusions in pottery, and some man-made glasses have also been dated. A further use of the method is based on the fact that fission tracks disappear if the substance is heated about ?

The study of earth history by correlating archaeological events to the timing and sequencing of geological events. Specifically, it is the dating of archaeological data in association with a geological deposit or formation, such as the dating of Pleistocene human remains in the context of glacial advances and retreats. The term is applied to all absolute and relative dating methods that involve the earth's physical changes, like radiocarbon datingdendrochronology, archaeomagnetism, fluorine testing, obsidian dating, potassium-argon datingthermoluminescence, and varve dating.

The time taken for half of a given amount of a radioactive substance to decay into a non-radioactive substance. It is also defined as the time taken for half the quantity of a radioactive isotope in a sample to decay and form a stable element. It is the basis of radiocarbon and other radiometric dating methods. This decay rate, expressed as a statistical constant, is different for each isotope.

Potassium argon dating in archaeology a sample, such as a piece of wood, has half of the original amount of radiocarbon remaining, then a time equivalent to the half-life has passed since it died. The half-life of radiocarbon is ? The half-life potazsium effect determines the *potassium argon dating in archaeology* agchaeology range over which a radiometric dating method is potentially useful. General term for volcanic ash or any solid material ejected during a volcanic eruption.

Tephra beds are ideal stratigraphic markers because they are deposited instantaneously; they may be dated by potassium-argon dating and fission track dating. A method for the relative dating archaeologgy horizons in volcanic regions by identification of different layers of ash **potassium argon dating in archaeology.** Tephra layers beds are ideal stratigraphic markers because they are deposited instantaneously. Also, the chemical potassium argon dating in archaeology of tephra volcanic ash is unique for each eruption.

If artifacts lie below tephra known to have come from a certain eruption, potassim artifacts predate the eruption. Tephra layers may be dated by potassium-argon dating and fission track dating and they can sometimes be tied in to absolute chronology where dating zodiac signs compatibility dates can be obtained from material contemporary with the deposit. To establish a chronology it is necessary to identify and correlate as many tephra units as possible over the widest possible area.

In the Mediterranean, deep-sea coring produced evidence for the ash fall from the eruption of Thera, and its stratigraphic position provided important information in the construction of a relative chronology. The identification of multiple tephra beds may give bracketing ages for intervening strata. Tephrochronology has also been used to date cating advances, sea level changes, and alluvial fans. Solidified volcanic ash or dust; a soft, porous rock consisting of the compacted volcanic ash or dust.

Tuffs may be grouped as vitric, crystal, or lithic when they are composed principally of glass, crystal chips, or the debris of pre-existing rocks, respectively. They can often be dated by potassium-argon dating.