Dating in Archaeology

Chronological dating or simply dating is the process of attributing to an object or event a date in the past. Archaeologists have access to various techniques for dating archaeological sites or the objects found on those sites. There are two main categories of dating methods in archaeology: indirect or relative dating and absolute dating.

Relative dating includes methods that rely on the analysis of comparative data or the context (eg, geological, regional, cultural) in which the object one wishes to date is found. This approach helps to order events chronologically but it does not provide the absolute age of an object expressed in years. Relative dating includes different techniques, but the most commonly used are soil stratigraphy analysis and typology.

On the other hand, absolute dating includes all methods that provide figures about the real estimated age of archaeological objects. These methods usually analyze physicochemical transformation phenomena whose rate are known or can be estimated relatively well. This is the only type of techniques that can help clarifying the actual age of an object. There are several absolute dating methods like Radiocarbon dating, Thermo luminescence, Potassium-argon dating, Dendrochronology or Tree-ring dating, Amino acid dating, etc. But Radiocarbon dating and Thermo luminescence are the most popular dating methods which are used world widely

The Radiocarbon Dating or Carbon Dating:

It is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late 1940s at the University of Chicago by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960.

It is based on the fact that radiocarbon^[1] C is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting^[2] C combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire^[3] C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment and thereafter the amount of^[4] C it contains begins to decrease as the^[5] C undergoes radioactive decay. Measuring the amount of^[6] C in a sample from a dead plant or animal, such as a piece of wood or a fragment of bone, provides information that can be used to calculate when the animal or plant died.

By this method makes dating reliable up to about 50,000 years which is very good time span in case of archaeological dating. The main drawback of Radiocarbon dating method is that it cannot date the inorganic sample directly. Metal grave goods, for example, cannot be radiocarbon dated, but they may be found in a grave with a coffin, charcoal, or other material which can be assumed to have been deposited at the same time. In these cases, a date for the coffin or charcoal is indicative of the date of deposition of the grave goods, because of the direct functional relationship between the two.

For decades after Libby performed the first radiocarbon dating experiments, the only way to measure the^[7] C in a sample was to detect the radioactive decay of individual carbon atoms and this method is also known as "beta counting". In the late 1970s an alternative approach became available directly counting the number of^[8] C atoms in a given sample, via accelerator mass spectrometry (AMS). AMS has two further significant advantages over beta counting, it can perform accurate testing on samples much too small and it is much faster compare to beta counting. For beta counters, a sample weighing at least 10 grams is typically required. Accelerator mass spectrometry is much more sensitive, and samples containing as little as 0.5 milligrams can be used.

In India, the first series of radiocarbon dating of samples of archaeological interest were measured by S. Kusumgar, D. Lal and R. P. Sarna, Radiocarbon Laboratory of the Tata Institute of Fundamental Research, Bombay (Modern Mumbai) dated May 31, 1963. The samples from 10 nos different sites (1. Afyeh, Nubia, Egypt, 2.Ahar, Rajasthan,3.Burzaham, Kashmir,4.Chandoli, Maharashtra, 5. Kalibanga, Rajasthan,6.Lalipur, Uttar Pradesh,7.Lothal, Gujarat,8.Navadatoli, Madhya Pradesh,9.Nevasa, Maharashtra & 10.Rajgir, Bihar) were sent by Shri A. Ghosh, Dr. H.D. Sankalia and other archaeologists.

The following conclusions regarding protohistoric chronology of India were made by the result of this radiocarbon dating: The Central Indian Chalcolithic cultures that were archaeologically placed at c.1000 B.C. are now found to belong to the latter half of the second millennium B.C. In point of time, the western Chalcolithic cultures appear as derivatives from the central Chalcolithic. Also, the end of Harappa culture came appreciably earlier than estimated archaeologically. Furthermore, the late phase of Harappa culture has been shown to be considerably earlier than that estimated by archaeologists. It also appears that the devolution of Harappa culture did not take very long. Lastly, the C^[9] date of a sample from Utnur has shown that the southern Neolithic culture was contemporary with the Harappa culture of the North [Radiocarbon dating: Results by S. Kusumgar, D. Lal and R. P. Sarna,Tata Institute of Fundamental Research, Bombay-5,dated-May,31,1963].

The Thermo-luminescence Dating:

Thermo luminescence dating (TL) is the determination by means of measuring the accumulated radiation dose of the time elapsed since material containing crystalline minerals was either heated (lava, ceramics) or exposed to sunlight (sediments). Thermo luminescence is the release in the form of light of stored energy from a substance when it is heated. All ceramic material contains certain amounts of radioactive impurities (uranium, thorium, potassium). When the ceramic is heated the radioactive energy present in the clay till then is lost, and fresh energy acquired gradually depending on the time of its existence.

The Thermo luminescence observed is a measure of the total dose of radiation to which the ceramic has been exposed since the last previous heating, i.e. in the kiln. For calculating dates the sample is heated up to 500[0]C and thermo luminescence observed as a glow is measured with very sensitive instruments. The glow emitted is directly proportional to the radiation it received multiplied by the years. Thermo luminescence measurements were suggested by Farrington Daniels of the University of Wisconsin in America (1953).

Thermo luminescence dating is used mostly on pottery and other inorganic materials such as burnt flint etc. It is a very popular dating method in archaeology because not only can it date pottery, the type of material mostly can be found when excavating, but it can also date further back than 50,000 years unlike radiocarbon dating and it much cheaper in comparison to other dating methods.

The first archaeological TL dates for India came out of the Oxford Laboratory, which is the birth place of thermoluminescence (TL) dating (Huxtable and Others, 1972). The TL dating in archaeology started in India in the seventies both at the Bhabha Atomic Research Centre (BARC), Bombay, and the Physical Research Laboratory (PRL), Ahmedabad (Nambi and Others, 1979;Agrawal and Others, 1981).

As per the summaries the TL results obtained on the Indian archaeological sites, mostly at the two laboratories, PRL, Ahmedabad and BARC, Bombay (Singhvi and Others., 1983). As per Thermo luminescence in Archaeology: An Indian Perspective by A.K.Singhvi and D.P. Agarwal, Physical Research Laboratory (PRL), Ahmedabad, India, the TL application at Sringaverapura dated the local Ochre Coloured Pottery (OCP) Culture to c. 3000 yr BP (Singhvi and Others, 1983) [Here, BP stands for ‘Before the Present and the present is conventionally fixed at 1950]. The dating of Sringaverapura has also been instructive in that it provided for the first time, a date to the Pre-NBP, Black Slipped Ware which overlaps with the Northern Black Polished Ware (NBPW), a culture archaeologically considered to be coeval with the epic Rāmāyaṇa. Thus the Rāmāyaṇa episode could not be earlier than c. 750 BCE (Agrawal and Others, 1981). Similarity, the South Indian Megalithic Culture has been dated for the first time to c. 3200 yr BP (Singhvi and Others, 1983).

Another important contribution has been the dating of burnt clay at Kurnool, an Upper Paleolithic site, that has provided a date of about 18000 yr BP (Nambi and Murty, 1981) and the Neolithic levels of Mahagara have been dated to c. 3500 yr BP (David and Sunta, 1980). A corded ware culture from Manipur has been dated to ca. 3600 yr BP, (Singhi and Others, 1983). Similarly a quartz inclusion TL dating of Savalda-Jorwe Culture at Daimabad has yielded a date bracket 4000-5000 yr BP (David and Suntan, 1980) [ Thermo luminescence in Archaeology: An Indian Perspective by A. K. Singhvi and D. P. Agarwal, Physical Research Laboratory (PRL), Ahmadabad, India].

In an attempt to provide a chronology for Indian archaeological sites, the radiocarbon dating technique had been started since year 1963 and an extensive pottery dating was initiated by Thermo luminescence dating method during 1978-1979. Both radiocarbon dating & Thermo luminescence dating methods are destructive type i.e. the samples are deformed during these processes and it will not in condition to reuse again in archeological purpose. That is why; many archeologists discourage these techniques to send their valuable samples for radiocarbon & TL dating. But in modern days, using AMS in radiocarbon dating, the sample size has been reduced to 0.5mg to 1gm and it determines the date precisely within few hours.

Now, India has three AMS unit in his own in respective of around 45 no’s AMS units in whole world. So, India is in a good position to date huge no’s samples quickly. In case of Thermo luminescence dating method, each lab has a sample size that they require to achieve a result, which can range from 100 mg to 1 gram. Now, collecting simple size 1gram is not big issue in case of big sized artifact like temple materials, big statue, broken pottery etc excepts any small ones like coins, etc. So, the government should promote the absolute dating techniques in archeological field more extensively to date the historical article and cultures and cross-checking the previous chronological dating data which had been fixed by relative dating methods.

Unfortunately, this method is not yet being used in India on a regular basis. Even all over the world, this method has been used only experimentally, not to recover history. Thus, in many cases, where this method was highly needed, the real truth remains elusive. And as a result of not using such scientifically sound methods, some people make comments like ‘the authenticity of history is doubtful.’

If it is possible now or if it could be done someday in the future, it would add a useful dimension to our understanding of the meanings, significance, and value of the inscriptions; and researchers will be able to gain proper knowledge about how they were used and how they acted as objects in the discussion of social relations. If the method is applied, people will understand easily by examining various temples, statues, ancient artifacts and carvings etc. and find out exactly what period they were built on. Then we will find out which king was ruling in that place at that exact time, and thus, people may able to gain a thorough knowledge of their religious beliefs, culture, and society. Not only the established views will be changing more or less in some cases by applying this method, but also this will make some statements stronger by supporting them scientifically. In addition, it may generate some new ideas and lighten up some unknown facts.

It seems that historians and epigraphers have studied copperplates in very specific ways that framed within the fields of textual scholarship. And the manner in which they were interrogated, focusing exclusively on copper-plate texts, is largely determined by the methods used in the textual scholarship. However, the contributions that have been made and continue to be made cannot be denied even for a moment as the texts of these inscriptions provide us with a great deal of information about various different aspects of the developments that took place during this period.

The fact that most recorded not only land grants but also the revenue accrued was interpreted as reflecting a major socio-economic shift. Their collective appearance in the epigraphic record and rapid spread throughout the subcontinent was thus seen as reflecting the emergence of a feudal society.^[10] In early and early medieval period they have continued to constitute a main source of evidence for studies that have attempted to reconstruct the nature of the state and chart changing socio-economic dynamics. This appreciation of the value of the copperplate charters as a category of historical evidence has recently found expression in a number of studies that have consciously focused on them to reconstruct the changing socio-economic and political dynamics, Historical geographies [A limited number of studies^[11] have also considered the locational geography of the charters and identified patterns in their distribution to provide insight into regional geopolitics and political alliances, the spread of land grants and Brahmanical institutions, and the development of agrarian economies over time] that occurred in particular regions over time. The value of the copperplate charters as a category of evidence is beyond doubt.

Equally, of course, with considerable importance, the purpose of investing in the study of the copper plate charters with the archaeological approach is not merely to increase the textual scholarship. Judging by the comparison of historical periods, the way in which little archeology has been conducted across India; it seems that the archeological methods need to be revived to know the real fact of that time more generally.

This would necessarily involve the archaeological investigation of sites and objects like shrines, idols, statues, etc. that is not directly related to the epigraphic records at all. Ultimately, this would raise a set of concerns involving the relationships between archaeology and texts, and archaeological and historical scholarship in the study of India's past, and of course, it will restore history through the scientific method and strengthen the relevant theories more. Besides, archeology needs to have its own unique approach to the investigation of historical periods without confining it to a limited subject. The above-mentioned techniques and problems cannot be applied and resolved respectively overnight. Yet, as the results of this study suggest that such areas (which demand archeology and texts of the charters must be studied together) will not only open up fruitful opportunities for further research but also provide several ways in which researchers may discuss them further.

Footnotes and references:

[1]:

[2]:

[3]:

[4]:

[5]:

[6]:

[7]:

[8]:

[9]:

P.V. Kane, History of Dharmaśāstra, vol. I and II, part II, p. 860.

[10]:

R.S. Sharma, “Decay of Gangetic Towns in Gupta and Post-Gupta Times,” In Proceedings of the Indian History Congress, pp. 92-104.

[11]:

Such as, H.D. Sankalia, Studies in the Historical and Cultural Geography and Ethnography of Gujarat; A. Bhattacharyya, Historical Geography of Ancient & early Medieval Bengal; U. Singh, Kings, Brahmanas, and Temples in Orissa: an Epigraphic Study AD 300-1147; N. Verma, Society and Economy in Ancient India: An Epigraphic Study of the Maitrakas (c. A.D. 475-775) etc.