Evolution -- Dating Methods
Jul 11, New method for dating copper and bronze artefacts Voltammetry of microparticles used to date archeological artefacts with soils or sea air, a layer of tenorite (CuO) continuously forms over the primary cuprite patina. [relative] analyzing the patina (which forms from chemical reactions) on the [ absolute] a dating technique in which the position of the earth's magnetic poles can we can calculate a range of years the buildings were orientated to these events [absolute] measuring the decay of potassium in argon which is used to date. The estimation of the age relationship between the specimen Patination, though in itself an method has been used in the dating of the Australopithecinae.
Relative Dating of Rock Art Given the current status of direct chronometric dating methods for Arabian petroglyphs, it is rare that the precise age of a rock art panel can be determined. However, all is not lost, and it is possible to establish a temporal sequence that can be quite edifying. To progress, it is essential to apply the second type, or relative, dating. The term refers to the fact that an approximate date can be inferred by comparison with something else of known age.
In this case, a rock art panel may be judged to be younger, older or basically contemporaneous with another petroglyph, a site, an artifact, or other evidence of known antiquity. Relative dating, although somewhat less satisfying than absolute dating in terms of precision, is considerably more successful for petroglyphs. Often there are multiple sites of varying ages nearby and the petroglyph itself may be a palimpsest of images created through the ages.
On rare occasion, archaeological deposits can accumulate up against a petroglyph panel, concealing part or all of the art. In that case, it may be possible to discern a minimum age for the art because its creation had to precede the archaeological deposit covering it. This is not typical of the rock art in Saudi Arabia, however, which tends to be exposed and lacking any settlement or camp next to the cliff face.
A palimpsest of animals from different ages at Shuwaymis: Faint images of Neolithic aurochsen wild cattlemore recent camels and cavalryman, still younger men with exaggerated hands. The patina is darker on the older images and the newer images are brighter. Although it is difficult to state the absolute ages of most of the rock art studied in this project, there are certainly general trends, best estimates and bracketing dates, which will be provided whenever possible.
Clues to relative dating include: The earth at that time was considerably colder and the ice caps were much larger than they currently are. Many species, such as mammoth and woolly rhinoceros thrived in Eurasia and the mammoth, mastodon, camel and giant sloth lived in North America. Around 10, BCE, a significant climate change occurred, altering environments, flora, and fauna in most parts of the world.
Following the Pleistocene, the Holocene or Recent epoch, witnessed a marked global warming that we still experience today. The climate was not stable, however, and around BCE, monsoon patterns shifted northward, causing the Arabian Peninsula to be more like a savanna than a desert.
Rivers flowed, lakes formed, and the human inhabitants, flora and fauna embraced this lusher environment. The Holocene Wet Phase, as it is called, fluctuated greatly between humid and dry periods and then reverted to a more consistent arid condition around BCE, as the rain belt retreated southward Parker et al. The oldest known petroglyphs in Saudi Arabia are believed to date to the Neolithic period or Early Arabian Pastoral, which appears to coincide with at least part of the Holocene Wet Phase.
These images are typically carved or pecked deeply into the rock surface.
Compared to subsequent periods, the older Holocene Wet Phase Neolithic images usually have a patina that formed after the art and is evenly dispersed over both the images and the background. Later petroglyph artists took advantage of desert varnish, a dark, often shiny glaze that forms on rock surfaces in very arid environments.
By scratching through the varnish and revealing the lighter colored underlying rock, it was possible to create bold images. Many of the rock outcrops bearing Neolithic images never developed dark desert varnish at all.
The uniformly light color of the sandstone surfaces explains why the Neolithic artists had to incise or peck the images deeply into the rock: Larger than life figure of Neolithic hunter at Jubbah with his bow and bow case or quiver.
Rock Art Dating Methods: Problems and Solutions
A throwing stick protrudes from the case. The most common Neolithic scenes are of hunter-herders with bows and arrows and throwing sticks, which are similar to a boomerang. The hunter is usually aided by a pack of hunting dogs. Although these people were part-time pastoralists with herds of sheep and goats, the art suggests that hunting played an important role in their subsistence. The relatively high frequency of hunting scenes in contrast to pastoral ones could also reflect the greater risk invested in hunting forays, and therefore perhaps more accompanying rituals.
Wild species targeted as prey by Neolithic hunters included: A Neolithic scene at Shuwaymis illustrates a confrontation with a lion, but such depictions are more common in later periods. The leopard and cheetah are also shown on Neolithic panels at Shuwaymis, but not with the frequency of prey animals.
Fairly realistic female figures at Jubbah, possibly Chalcolithic in age, are elaborately clothed in ornate dresses with a sash cinching in the waist to highlight their physique. They also lack facial features, although their hairstyles are more clearly depicted than for the Neolithic men. The method of creating the figures is constant, with deeply carved outlines and little or no removal of patina. Their antiquity is supported by the absence of associated horses, camels, or writing.
Holocene Arid Phase This petroglyph panel at Jabal Yatib was shallowly scratched through the dark desert varnish. The subjects lion, palm trees, camels, horses, and writingas well as the technique, indicate that it was done after the Holocene Wet Phase. At the end of the Chalcolithic, the method of creating rock art shifted away from the laborious removal of large quantities of stone by making deep grooves and large recessed areas.
After about BCE, when the Arabian Peninsula returned to extremely arid conditions, the rock surfaces in many areas started to form a dark brown to black desert varnish. These outcrops became the canvases of choice, since the removal of the thin veneer of desert varnish resulted in a high contrast between the subject and the background. Scratching through the thin surface patina revealed lighter-colored gold or pink sandstone beneath.
The often dramatic images that resulted from this new technique highlight the outline or body of a figure by being lighter than the surrounding background.
With this new method, the task of ancient artists was greatly facilitated, and they were able to create single figures or entire scenes relatively quickly.
In contrast to the deeply incised Neolithic images, these shallower petroglyphs may fade more easily as patina gradually forms inside the subject area, rendering them less visible.
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. 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.
Principles of Prehistoric Archaeology. Chronology: Relative and Absolute Dating methods
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.
The observation of the amount of patina on a stone may be used at sites where there is a long sequence and demonstrates that those tools which lie in the bottom level may have more patina than those in the upper levels. The different types of tools from the river gravels, terraces of rivers or lakes can be differentiated in the relative amounts of patina on the basis of which of the relative ages can be assigned on the artefacts. Goodwin who worked extensively on the patination in lists many variables involved in patina formation as well as different type of patination.
Rock Art Dating Methods: Problems and Solutions - Arabian Rock Art Heritage
That can be used fruitfully for the tools from stratified deposits. Carbon Dating - Radiocarbon dating is a chemical analysis used to determine the age of organic materials based on their content of the radioisotope of carbon The method was developed by Willard F.How to Age Brass
Libby and a team of scientists at the University of Chicago. In Libby received the Nobel Prize for his method to use Carbon for age determinations in archaeology, geology, geophysics, and other branches of science. It subsequently evolved into the most powerful method of dating and Holocene artefacts and geologic events up to about 50, years. By radiocarbon method one can date different types of organic or inorganic materials as long as they consist of carbon.
The method is actually devised to measure the amount of low level radioactivity of carbon remaining in ancient and dead material of organic origin. Radiocarbon 14C dating is the most widely accepted technique for studying the chronological relationships of archaeological complexes.
Using the radiocarbon method as a source of objective information, we are able to build Stone Age chronologies as well as establish the primary chrono-cultural boundaries. The earth's crust contains potassium of which isotope K40 decays to A40 at a known rate.
The ratio of potassium to Argon may be measured to ascertain date of minerals and rocks in a deposit.
Dating Methods in Prehistory
This method is able to cover a wide range of time even far greater than C method because, the half life of the radioactive potassium is million years. The method has proved quite useful in dating some hominid fossils as employed in the site of Olduvai Gorge in east Africa where the remains were as old as 1.
The advantage of the method is that it works well in case of the sites which areyears old. But the disadvantage of the method is that it can be applied to only to those rocks and minerals which are rich in potassium. Therefore the method is restricted to the areas where volcanic rocks rich in potassium are available.
Aitken and co- workers. Initially designed to date archaeological ceramics, it was subsequently extended to other mineral materials, such as burnt flint. This is based on the fact that objects such as pottery that have been heated in the past can be dated by the measurement of their Thermoluminescence TL glow. Thermoluminiscence TL is the emitted light in the pottery which can be measured. If the ground up pottery is reheated, it emits light.
The phenomenon results from radio-active influence of the metallic elements like uranium and potassium present in the clay and surrounding soils.