DATING METHODS IN ARCHAEOLOGY
Definition. Absolute and relative dating methods have been used to establish tentative chronologies for rock art. Relative dating refers to non-chronometric. Chronological dating, or simply dating, is the process of attributing to an object or event a date Relative dating methods are unable to determine the absolute age of an and relative dating applications used in geology, paleontology or archaeology, clarifying their meanings, classifying their uses according to dates and. of archaeology. absolute dating technique exhibit chronology in terms of years. It offers Under relative dating there are different methods such as stratigraphy, typology, The simple meaning of stratigraphy is the study of strata or layers.
Typology - An archaeological site mainly consists of artefacts and tools. The tools found in the site are classified on the basis of their form or shape and accordingly different categories or types are made.
These are then arranged from simple to elaborate or from poorly preserved to well preserved or from crude to refine etc. Then a relative antiquity is derived based on the presumption that simple, poorly preserved and crude tools are earlier than the elaborate, well preserved and refined ones. The typological method although was used for obtaining relative dating earlier, it has come in for much criticism now-a-days.
According to Wheeler 'the values of typological classification are liable to be local rather than universal' but when the method is used in corroboration with stratigraphic method, it may become very helpful'. The method is based on the fact that artefacts change in predictable ways through time. Among all other artefacts it is found that pottery changes with time frequently and a sequence of pottery design can thus be worked out.
By detecting this trend of change, an archaeologist can trace associated cultural changes and make short term time distinction.
While the excavation of grave was carried out in Egypt, Petrie found that the graves were associated with varied pottery. He analyse the features of pottery such as handles of pot and worked out a sequence showing their change, progressing from functional entities to mere decorations. The changes on pots were than correlated with other artefacts from graves and he finally ended with a series of numbered pottery stages that he labelled 'sequence dates'.
This method was later on applied by the great anthropologist, Kroeber in determining the relative age of some sites in south western United States, Mexico and Peru. Cross Dating - Cross dating involves the comparison of artefacts found in different stratigraphic levels.
Chronological dating - Wikipedia
The method is based on the fact that the similar artefacts are approximately contemporary. The greater the similarity, the closer the ages. Certain artefacts like coins, pottery, arrowheads etc. When such type of objects are found in two different sites, according to cross dating sites are considered roughly the same age. Different pottery types which changes very frequently with time and hence occur for a very shorter period of time are better 'index fossil' or 'horizon marker' than others.
Fluorine, Uranium, and Nitrogen analysis: Prehistoric sites often consist of many bone remains. The basic principle of the method is that the longer a bone will be placed in soil, the more fluorine will be caught in and hence can suggest a relative date.
All bones whether of animal or of human lying in the same level exhibit similar fluorine percentage in them. Therefore, if the quantity of fluorine remains same in both kinds of bone, it is sure that they belong to the same age.
The bones acquired from a lower level show more fluorine in them whereas the bone remains coming from the upper level contains less fluorine. Relative ages of different bones at the same site thus can be established by measuring their fluorine contents.
The method cannot provide an absolute age because the amount of fluorine differs from soil to soil, which gives a differential rate of absorption. Like fluorine, uranium or nitrogen content of the bones also can be measured.
Since fluorine and uranium levels in the bone increase with time, while nitrogen decreases, such measurements helps to place in sequence the cultural phases with which the different bones may be associated.
In fact the analysis of fluorine, uranium or nitrogen is regarded as one of the very important technique for relative dating. Palaeontology - Palaeontology, the study of fossilised remains of bones in archaeological sites also provide relative dates.
The method is based on the fact that some animals migrate or become extinct with the change of climate. That is, climate has a direct relationship with the presence or absence of certain animals. For example, if evidence for Elephas antiques a forest elephant is found, one can assume a temperate climate, while the presence of E. Likewise, it is found that in North America the arrival of man caused the extinction of mammals such as the mammoth, horse, camel and several species of bison.
These can be dated approximately about B. C However, a margin of years error might be there as all of them have not become extinct at once and some have lived in isolated areas in which case the dating of fauna associated with other evidence is inexact and misleading. Smaller species of animals like rodents, birds, some molluscs and snails are found very sensitive to changes in climate than the larger mammals.
In Northern Ireland it has been possible to show changes in coastal environment since the time of human occupation by studying changes in tidal - zone molluscs found in archaeological sites.
Palynology - Lennart Von Post, a Swedish Scientist, was the first to develop this palaeobotanical method in By this method a microscopic analysis of pollens extracted from trees are used to identify various trees and a pollen diagram is prepared.
The pollen diagram in which relative frequencies of various species are plotted helps in tracing out the changing vegetation of an area. Acid peat or bog deposit is ideal sources of animal pollen, but dry sites, and clays contain enough pollen to provide a sequence.
Pollens in soil underlying or overlying archaeological sites may be correlated with the already known regional pollen sequence and the age of the site thus can be dated. A very good example of application of pollen method is the archaeological site at Choukoutien in China. Patination - There is no precise definition for the term patination though it generally means chemical alteration of rock surfaces exposed to atmospheric conditions. The amount of patina on the stone is an index of its age valuable for relative placement of the stone artefact in the technological development.
The chemical alterations of the stone are usually brought about by the action of iron oxides through time. Samples which are in contact or near the roots of any plants or trees should not be collected because these roots may implant fresh carbon into the specimens. Handling with bare hands may add oil, grease, etc to the sample.
Therefore, it is better to collect samples with clean and dry stainless steel sclapels or squeezers. It may also be collected with the help of glass. Stainless steel, glass, polythene and aluminium are free from carbonatious organic material. Therefore sampling should be done with such material only. Samples should be sundried before pacing in aluminium thin foils and placed in a glass jar or secured safely in thick polythene covers.
Before pacing the soil should be removed while it is wet at the site. Method of Sample Recording: Before removing the sample from the site we should note down the data or the environment of the sample. We have to fill the data sheets, which should be done at the time of sampling and should be submitted along with the sample to the dating laboratory.
These sheets require data on environment and stratigraphy of the sample, and archaeological estimates of its dating. This data help in obtaining and objective interpretation of dates. Limitation and Errors of C Dating: There are a number of technical difficulties inherent in this method of dating.
The first difficulty is that the quantity required for a single determination is comparatively large. It will be difficult to obtain sufficient quantities of samples, especially in the case of valuable museum specimens. The second difficulty is that the radio active decay does not take place at a uniform rate but is a random process, and is therefore, governed by the laws of statistical probability.
Another difficulty that has to be taken into serious consideration is the possibility of uneven distribution of radio carbon in organic matter. If the specimen is analyzed after having been exposed to contamination by carbon compounds of an age younger than its own, radio carbon age is liable to be reduced.
The best results can be obtained from specimens, which were preserved under very dry conditions, or even enclosed in rock tombs of the like. Very dangerous contamination is done, very often, by the growth of fungus and bacteria on the surface of the specimen which even when removed from the specimen may falsify its actual age.
Though there are some drawbacks and technical difficulties, the radiocarbon method is a reliable, efficient and most useful method of dating the archaeological specimens.
We are helpless in the case of contamination done by the natural agencies in the past, but we can overcome most of the difficulties by paying sufficient care and attention while collecting the samples. It is the duty of an archaeologist to study with care the condition of preservation of specimens submitted for analysis and, in fact, to submit only specimens that can be regarded as fool-proof as is possible in the circumstances.
A major application of dendrochronology in archaeology, as a tool for establishing dates from the samples of wood and articles made out of wood is not only in working out primary chronologies but also in cross checking the already known dates by other methods.
Often, the tree-ring analysis from a site can give strong clues about the length of occupation, certain periods of building or repair activities at the site. Another application of tree-ring analysis is the inference of past environmental conditions, which is extremely useful to the archaeologists. The modern science of dendrochronology was pioneered by A. Tree ring analysis is based on the phenomenon of formation of annual growth rings in many trees, such as conifers.
These rings are shown by the trees growing in regions with regular seasonal changes of climate. As a rule trees produce one ring every year. Optically stimulated luminescence OSL [ edit ] Optically stimulated luminescence OSL dating constrains the time at which sediment was last exposed to light. During sediment transport, exposure to sunlight 'zeros' the luminescence signal. Upon burial, the sediment accumulates a luminescence signal as natural ambient radiation gradually ionises the mineral grains.
Careful sampling under dark conditions allows the sediment to be exposed to artificial light in the laboratory which releases the OSL signal. The amount of luminescence released is used to calculate the equivalent dose De that the sediment has acquired since deposition, which can be used in combination with the dose rate Dr to calculate the age. Dendrochronology The growth rings of a tree at Bristol ZooEngland. Each ring represents one year; the outside rings, near the bark, are the youngest. Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings.
Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year. Dendrochronology has three main areas of application: In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands.