3 Archaeology and Sciences Part II
Ravi Korisettar
1. Palaeontology
As we all know animals constitute an important component of human diet, especially among hunter-gatherers, both in prehistoric and historic times. General paleontology forms part of geological studies, whereas Quaternary (the last 2.5 million years) palaeontology is of relevance to archaeology for reconstructing man-animal relationships, in terms of animals that were hunted by prehistoric hunter-gatherers and those animals that have been domesticated since the beginning of agricultural way of life during and Neolithic and post-Neolithic times.
The Subhimalayan region and the Narmada basin have received greater attention of palaeontological research in India, Prior to the emergence of absolute dating methods paleontological methods were applied for reconstructing chronology. A large variety of animal remains comprising mammals, ostrich egg shells, reptiles, amphibians, fish and microvertebrates obtained from Quaternary strata in the river basins of India have helped identified animal native to India and exotic ones. As this assemblage comprises some of the exotic animals it is understood that majority of large mammals may have migrated to India from Egypt, Arabia, Central Asia and North America. Similarly it has assumed that rhinoceros, horse and camel all originating in North America may have evolved further in some regions of Central and West Asia before reaching India. Palaeontological research in India holds promise for the application of multidisciplinary research for a better understanding of man-animal relationship.
2. Archaeogenetics
This is a new emerging area of investigation that aims at tracing the origins, evolution, expansion and chronology of human ancestors based on the study of aDNA molecules in terms mitochondria and Y-Chromosome. These are preserved in fossilized bones of Neanderthals and early Homo sapiens from different archaeological contexts in Europe and northern Asia. So far such studies are possible for lack of fossil evidence.
These studies have helped in understanding whether modern humans (Homo sapiens) emerged as a separate species roughly 200,000 years ago in Africa or as the consequence of evolution within a polytyic species spread across the world.
3. Archaeo-linguisitcs
The origins and spread of agriculture is also accompanied by the spread of language families. The centres of discussion being central Asia and Southwest Asia. Colin Renfrew and Peter Bellowood have pioneered research in this area. It is suggested that origins of agriculture supported population growth and in turn triggered population movements, which in turn displaced or absorbed the much smaller forager populations. Population movements since the Neolithic times have resulted in widespread of occurrence of different language families with their centres of origin either in Southwest Asia or Central Asia. This is also reflected in DNA a studies of modern population in the Indian subcontinent. The linguistic geography and phylogeny of Indo-European point towards central Asia as the region with languages most closely related to the Indic languages of India, and most evidence is argued to suggest the dispersal of Indo-European languages westward to Europe in the Bronze Age, which has received recent support from archaeological DNA. The timing of their arrival in the subcontinent is still unclear but genetic evidence does support mixing between ancestral South Indian and Central Asian related northern Indians over the past 4200 years. Although a case can be made that the Dravidian Languages of India do indeed have a plausible distant relationship with ancient Elamite languages.
4. Archaeochemistry
The science of archaeochemistry provides a set of methods specifically to restore and conserve archaeological artefacts, including stone, soil, bone and metal. These methods are also applied to determine the composition, structure and properties of material used in the past.
The conservation and preservation techniques are employed to retrieve the physical and chemical properties of artefactual materials and helps in understanding the ancient techniques of production, fabrication, choice and provenance of raw materials.
The chemical study or analysis of soils associated with human activity is an important application of chemistry in archaeology. Thee soils are called anthrosols, ie. Soils altered by human activity as compared to natural soils. The extent of chemical alteration of these soils relates to both intensity and duration of settlement. Plant nutrients, organic matter, oxidation-reduction characteristics, pH values, and exotic contaminants are chemical soil factors reflecting human activities that can be quantified. Chemical analysis designed specifically for anthrosols, particularly phosphate analysis, can applied both qualitatively in the field and quantitatively in the laboratory. Phosphate analysis of anthrosols from a number of archaeological sites of Neolithic, Chalcolithic and Historical sites have been carried out in India.
Chemical analysis of soils associated with human activity in the landscape helps determine the duration and intensity of human activity in the past, reflected in the greater concentration of natural elements like carbon, nitrogen and phosphorus. Phosphate analysis of anthrosols from a number of archaeological sites of Neolithic, Chalcolithic and Early Historic sites have been carried out in India.
Chemical analysis of bones in terms of their elemental composition helps reconstruct prehistoric dietary practices. The measurement of fluorine/phosphate ratios from bones serves as a handy tool for determining the relative chronology.
5. Archaeometallurgy
Archaeometallurgy deals with the study of metallic artefacts from archaeological contexts for reconstructing various stages of procurement, processing and distribution of raw materials and finished objects, with implication for the economy of the communities that produced a variety of metal artefacts. Metallurgy involves the study of smelting, alloying, casting, craftsmanship of smiths etc. Further it also deals with the prehistoric techniques of procurement (by means of trade, exchange, mining, etc.) and sourcing of raw material (provenance studies). The chemical analysis of a variety of metal objects from Chalcolithic, Iron Age and Harappan sites has helped in understanding the procurement strategies of ores and solid metals, mineral resources and alloying techniques. It has been observed that Mature Harappan phase witnessed an upsurge of metallurgical activity and that copper technology was at par with contemporary civilizations. Continuity of casting of metal objects has been observed in the Chalcolithic cultures of India, though not comparable to the Haraapan.
6. Field Archaeology: the use of scientific instruments for survey and recording
Exploration and excavation are the two major components of any archaeological research design and are mutually exclusive. Systematic ground survey for locating archaeological sites, extent of archaeological activity, culture history of the settlement, etc. can be estimated prior to excavation and sometimes in lieu of excavation. It is suggested that field archaeology refers to techniques other than excavation used by archaeologists in the field and thus involves the use of a set of nondestructive field techniques employed for surveying sites of archaeological importance.
Since the last World War beginning with the use of aerial photos a number of remote sensing techniques have come into field archaeological surveys as spin-offs from advances in space research.5 Archaeologists searching for new sites use satellite images, drone operations and geophysical methods. These can be used in various combinations and are key elements of geographical information systems. Geophysical survey methods are part remote sensing surveys and a non-destructive method of site investigation. It has found its application extensively in Indian archaeology. Resistivity surveying, magnetometry, ground penetrating radar, acoustic reflection and thermal sensing are in use, among them resistivity surveying and magnetometry are most common.
7. Remote Sensing
Remote Sensing (RS) refers to the branch of science which deals with objects (surface or sub-surface features, in the context of archaeology) through measurements made from a distance (i.e., without being in physical contact with these objects). Remote sensing involves any techniques which capture geographic data by sensors at some some distance from the surface being recorded. Aerial photography is the earliest remote sensing tool used by archaeologists, and still continues to be in use.
It uses electromagnetic radiation (light) as the medium of interaction. Apart from visible light, sensors to detect electromagnetic radiation extending from the ultraviolet to the range of infrared and microwave regions are also used for remote sensing. Since the last World War beginning with the use of aerial photos a number of advanced remote sensing techniques have come into field archaeology as spin-offs from developments in space and aeronautic science. Archaeologists searching for new sites use satellite images, drone operations and geophysical methods. These can be used in various combinations and are key elements of geographical information systems. Geophysical survey methods are part of remote sensing surveys and a non-destructive method of site investigation. It has found its application extensively in Indian archaeology. Resistivity surveying, magnetometry, ground penetrating radar, acoustic reflection and thermal sensing are in use, among them resistivity surveying and magnetometry are most common.
Aerial surveys, and more particularly, documenting complete sites and excavations, can be traced back to World War I and military reconnaissance. The pioneering works of O.G.S. Crawford in England, Father Antoine Poidebard in Syria, Erich Schmidt in Iran, ushered this new field, which started with the principle of taking near vertical and oblique angled aerial photographs in different light conditions, to discover, locate and document archaeological sites and monuments. The airborne photography was later modified to suit the documentation necessities of archaeologists and low altitude photography played a crucial role in our understanding of excavated structures and monuments. The photographic equipment can be mounted in a balloon, kite, ladder or a boom mast depending upon the necessity. Depending upon the availability of high resolution equipments and area to be surveyed, different features like crop and soil marks in a landscape are clearly observable in aerial photographs that may indicate burial features. Considerable advancements have been made in aerial photographic techniques, with the development of drone technology or unmanned aerial vehicles, low altitude aeromeodelling can be achieved. Further, the drones can also be fitted with different sensors like thermal, infrared and Light Detection and Ranging (LiDAR) to enhance the images to even detect subsurface features like ditches, moats, etc. Aerial thermography, the airborne and satellite images have their own disadvantages in detecting sub-surface features.
8. Geophysical Surveying
Geophyiscal surveying techniques are part of remote sensing techniques. The last 60 years have witnessed increasing application of geophysical survey techniques in archaeological site surveying. They could be small scale field experiments by physicists and geophysicists to a variety of geophysical techniques for obtaining information about subsurface features. Detection of subsurface features is dependent on differences in electric, magnetic or elastic properties of rocks and sediments. There are two categories of geophysical methods viz., (i) passive and (ii) active methods. Under the passive method, magnetic prospecting (magnetometry), gravitational surveying and self-potential (SP) techniques are used for detecting buried features. Among these three techniques, the SP is considered to be the least expensive geophysical method in detecting archaeological features. The techniques under active methodsare (i) seismic or acoustic, (ii) electromagnetic, (iii) resistivity or galvanic and (iv) ground penetrating radar. The seismic method involves transmission of sound waves and measurement of the time of reflected ones based on density variations of buried features.
Therefore significance of the role of scientific instrumentation techniques in archaeological reconnaissance hardly needs emphasis, be it in the form of a simple handheld GPS for recording location details of artefacts to structures, but also sophisticated equipments like drone and laser scanners. One of the advantages of geophysical tools is that it can cover large areas of landscape for detecting the buried architectural features. The ground penetrating radar or GPR is considered a better technique when compared to other three, the range of detection being from a few mm to several meters beneath the earth surface. The GPR works on the principle of transmitting different wavelengths of radar signals and then measuring the continuity/discontinuity of reflected signals depending upon the properties of soil conditions and buried features. The use of electrical resistivity and magnetic gradiometry at Sisupalgarh helped in prospecting an area of 13 acres, which revealed presence of a 300-m long section of ancient road and its associated side streets and structures. The efficiency of GPR and other geophysical methods in prospecting a large area, which otherwise is not possible by regular excavation methods, a slow and expensive methodology by its nature, is an advantage for archaeological sites, has been indicated. All remote sensing methods are nondestructive and considerable economical. A geophysical survey carefully coordinated with an archaeological programme can provide valuable information for the planning and execution of the archaeological project.
In the Indian context, aerial photographs from the sites of Tughlaqabad, Sisupalgarh, are best examples of the use of such techniques in the documentation of archaeological sites.
9. Scientific Dating Methods: Select Science Based Methods
Prior to the emergence of absolute dating methods archaeological chronology was based on stratigraphy, typology, seriation, dendrochronology, varves, etc. though these come under the broad category of scientific dating methods these have been grouped as relative dating methods.
The development of absolute dating methods owes its origin to the science of nuclear physics which began to provide radiometric dates for the age of the earth (geological timescale) in terms of calendrical years. Following the radiocarbon revolution of the 1940s there have been a series methods helping dating both organic and inorganic materials coming from archaeological contexts.
9.1 Radiocarbon Dating
In the 1950s there occurred an event commonly referred t as Radiocarbon Revolution, attributed to Wilard Libbey who became a Nobel Laureate (1960). He discovered radioactive carbon (C-14) present in atmospheric and lithospheric reservoirs such as oceans, lakes and soil carbonates. In addition he explained the way it is produced in the atmosphere: the collision of fast moving neutrons (produced by cosmic rays) with atmospheric nitrogen causes transformation of nitrogen into C-14. This carbon is unstable in comparison with other stable carbons such as C-12 and C-13. This instability is characterized by radioactive disintegration that takes place at regular intervals of time till C-14 returns to its nitrogen state. This process is also called radioactive decay characterized by half-life, i.e. time taken for half of the atoms of carbon atoms to decay.
This discovery led Wilard Libbey to invent a dating method by measuring C-14 content in the archaeological sample, bone for example, based on the principle that C-14 production in the atmosphere has remained constant over a long period of time and that C-14 contained in a dead organism reduces itself by half every 5730 years and that an organism which died more 40,000 years ago does not contain even trace of C-14.
The atmospheric C-14 is an isotope (elements with similar chemical properties and different physical properties) of C-12 and C-13, with identical chemical behaviour and mixes homogeneously with them. They all dissolve in water, both rain and surface water, and are found in oceanic and fresh water bodies as wells as soil carbonates. Water is consumed by all living organisms and C-14 indirectly enters into their systems and continues to accumulate as long as the organism is alive. Following the death of the organism C-14begins to reduces through radioactive decay C-14.
With the development of Accelerator Mass Spectrometry radiocarbon dating secure dates by processing very small amounts of sample can be obtained. The original method developed by C-14 Libbey required several grams of dead organic matter from archaeological sites. The improved method known accelerator Mass Spectrometry requires only a few milligrams.
9.2 Dating Older Bones
For fossil or petrified bones belonging to more than a million years ago can also be dated by the method known as Electron Spin Resonance (popularly ESR dating method). The bones beyond C-14range can be dated more or less securely in calendar years. This method is based on the principle that electrons trapped in crystal lattice of bones when subject magnetic field begin to resonate and absorb electromagnetic power. The strength of resonance is directly proportional to the number of electrons that are trapped since the crystal was formed. It has been found that the tooth enamel is the ideal material for dating, and enamel decomposes very slowly and survives unaltered for long. In India an animal fossil from Palaeolithic site (old stone age) of Isampur in Karnataka has been dated 1.2 million years ago. And humans were in India as early as 12 Lakh years ago.
9.3 Potassium-Argon Dating
Potassium like carbon is abundant in the nature and it also contains some amount of radioactive potassium (K-40) which decays into Calcium-40 and gas argon. This gas escapes while igneous/volcanic rocks are being formed. When these rocks cool down, the argon gas is trapped in the crystal structure. This gas acculates over a period of time in the rocks and can released in the laboratory by heating and can then be measured. The quantity of argon is related to the amount of potassium and its age is estimated from its half-life (1,250 million years). Further improvement of K-Ar dating method was possible with theintroduction of argon-argon technique, which allows smaller samples to be dated. This method is ideal for dating early hominin fossils in East Africa as well as for dating volcanic tephra (see below).
9.4 Tephrochronology
Tephra are fragments of solid materials, such as crystal, glass and rock, ejected into the air by a volcanic eruption. They are airfall deposits and now provide a key to both dating and correlation, and hence are marker beds. These marker beds help in establishing a geologic framework for evolution.
Tephrochronologists and tephrostratigraphers study deposits and samples of these materials in order to characterize, correlate and date them. Tephra or volcanic ash where it is thick protects buried lithic and faunal material. In Indian there are a few studies helping in dating Pleistocene sites and human expansion out of Africa.
The fossiliferous and artefact rich sites of East Africa are the best examples of application of tephrochronology of early hominin evolution as they also preserve a detailed record of explosive volcanism. Much of our understanding of the patterns and timing of Plio-Pleistocene evolution in east Africa is based on tephrochronology and tephrostratigraphic framework. The well-known site of Jwalapuram in southern India where a tephra layer overlies the Middle Palaeolithic artefact horizon dated to 77,000 years ago.
9.5 Fission-track Dating
This method is applicable to dating volcanic glass (tephra) and other igneous rocks. The methods is based on counting microscopic tracks caused from the fission of uranium-238 in zircon and obsidian. This method has applications similar to k-Ar dating.
9.6 Luminescence Dating
This method can successfully applied for dating burnt clay objects such as ceramics, bricks, terra cotta, etc. The methods is known as thermoluminescence dating based on the principle that electrons trapped in crystalline minerals are released upon heating and emit light. The length of light is proportional to the time elapsed, since its last heating. This when applied to ceramics, for example, from archaeological context can determine the time elapsed since the pottery was last subject heating while manufacturing, during the course which previously trapped electrons are released and since the breakage of the pottery, the sherds’ crystal lattice will being to trap electron from the ambient radiation in the subsurface conditions.
9.7 Archaeomagnetism
(i) Archaeomagnetism is based on the principle that at archaeological sites mineral particles were magnetized at a specific time when the materials were heated, chemically changed or deposited. This magnetization can be used for relative or absolute dating.
(ii) The study of the magnetic properties of archaeological materials may also be of value in provenance studies, reconstructing artefacts and evaluating the nature of past technologies.
Web links
- https://en.wikipedia.org/wiki/Archaeological_science
- http://www.archaeology.su.se/english/about-us/events/conferences/xiv-nordictag2014/sessions/history-and-archaeology-a-very-long-engagement-1.154945
- https://www.enotes.com/homework-help/what-role-does-archeology-play-study-history-451129
- http://anthropology.msu.edu/anp203h-fs13/2013/12/08/why-is-archeology-important/
- http://www.saa.org/AbouttheSociety/Publications/ArchaeologyandYou/Chapter2TheScienceofArchaeoo
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