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An Encyclopaedia of Indian Archaeology v1.c12: 7 Environmental Archaeology

An Encyclopaedia of Indian Archaeology v1.c12

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7 Environmental Archaeology

7.1 Geochronology

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Geochronology, the science of dating events in earth history, essentially involves the study of repetitive superimposed features of the geological record, such as tree rings, varves and sedimentary cycles and of measurement of the ages based on the progressive decay of radiometric minerals, e.g. carbon 14 [5.3], potassium-argon, uranium-thorium, etc. These absolute methods are closely linked with relative dating methods where events are described as older or younger than other events and include the study of river/coastal terraces, palaeontology, palaeobotany and stratigraphy. Thermoluminescence [5.6] and fission-trace dating involve the measurement of microscopic features produced in certain minerals due to radioactive reactions. Palaeomagnetic studies record changes in the direction of the earth's magnetic field, while archaeomagnetism [5.2] measures the remnant of magnetism in archaeological material (pottery) caused by heat. Collectively these techniques have helped to push back the antiquity of man to three million years B.P. in Africa.

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Due to the paucity of materials susceptible to radiometric dating, Indian prehistoric chronology, despite the ¹⁴C dates now available, continues to be based largely on palaeontological and stratigraphical evidence. Lower Palaeolithic [4.2] artefacts both from the sub-Himalayan river terraces of the n.-w. and the basal alluvial deposits of peninsular India cannot be dated earlier than the late Middle or early Upper Pleistocene [9.8]. This dating is based partly on their stratigraphic occurrence and partly on a few associated index fossils, e.g. *Hippopotamus namadicus* and *Sus namadicus* for the Middle and *Elephas maximus*, *Equus caballus*, etc., for the Upper Pleistocene [15.1]. Recently, however, extrapolating from U/Th dates for corals and beachrock from s. Saurashtra it has been possible to date the Lower Palaeolithic artefacts from a fluvial gravel overlain by a fluvio-marine limestone in the Hiran valley to a period prior to 120000 B.P. [cf. 4.2].

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Stratigraphic evidence from the excavations at MAHADEO-PIPARIA and CHIRKI-NEVASA in the c. NARMADA and the PRAVARA valleys respectively and a few ¹⁴C dates on shells and drift woods from the 'Older Alluvium' deposits of Maharashtra and Gujarat suggest that the Indian Middle Palaeolithic cultures flourished in the subcontinent between 40000 and 15000 B.P. [cf. 4.3].

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Radiocarbon assay for shells from the BELAN valley, and from the Bhima and TAPTI valleys date the beginning of the Upper Palaeolithic stage [4.4] to c. 20000 B.P. For the Mesolithic period [4.5], ¹⁴C dates of charred bones from the primary sites of BAGOR and ADAMGARH and the chronostratigraphic evidence of artefacts in a ferruginized dune (*teri*) [9.5] which occurs as a raised (+6 m) shore-line in Dt Tirunelveli have placed these cultures to c. 7000 to 6000 B.P.

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Agrawal, D.P., & Kusumgar, S., 1974, *Prehistoric Chronology & Radiocarbon Dating in India*, New Delhi. Badam, G.L., 1976, in *Seminar on Palaeontology*, Geological Survey of India, Hyderabad (for Quaternary palaeontology in c. Narmada valley). Harper, C.T., ed., 1973, *Geochronology: Radiometric Dating of Rocks & Minerals*, Stroudsburg. Marathe, A.R., Rajaguru, S.N., & Lele, V.S., 1977, in *Sedimentary Geology* (in press) (for miliolite rocks of the Hiran valley). Michels, J.W., 1973, *Dating Methods in Archaeology*, London. For sites see respective entries in vol. II.—S.N. RAJAGURU

7.2 Neutron Activation Analysis

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Neutron activation analysis is part of a wide range of nuclear methods of analysis which are used for elemental analysis, particularly for those elements present at trace concentrations (less than 1 part in 10⁶) in sample. It is also used as a micro-analytical technique for major or minor constituents in case only a very limited quantity of sample is available for examination. This aspect is important in the examination of rare archaeological objects. The analysis is used in archaeology to determine the provenance and sometimes, indirectly, the period to which an artefact belongs. The object examined may be a potsherd, a bronze object, a painting or marble. Very small amounts of sample (~50 mg) will suffice for an analysis of a number of elements (typically 10 to 20) present at trace levels. The sample is irradiated in a nuclear reactor such as Apsara or CIRUS reactor along with suitable standards for the elements analysed. As a result of the irradiation the radio-isotopes of the elements which emit characteristic beta and gamma radiation are produced as they decay into stable nuclides. The energy of the radiation is used to characterize the element and its intensity is related to the amount of the element present. From the concentrations of a number of such trace elements in the samples it is possible to examine whether or not a given specimen belongs to a given group which corrresponds to a particular period or locality. Potsherds belonging to different ages like the Harappa [11.3] and other periods and different classes of pottery like the PGW [11.14] and Banas Ware [11.6.2] have been differentiated by the use of this technique. With this technique it is also possible to say whether an object such as a bronze or an oil painting is genuine or fake.

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Iyer, R.K., Rao, N.J., Krishnamoorthy, K.R., Sarkar Das, M., & Paramasivan, S., 1973, in Agrawal, D.P., & Ghosh, A., ed., *Radiocarbon & Indian Arch.*, Bombay, pp. 406-18.—M. SANKAR DAS, R.K. IYER & K.R. KRISHNAMOORTHY

7.3 Palaeoclimate

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The physical framework of the climatic system comprises the atmosphere, the hydrosphere, the cryosphere (ice masses and snow deposits), the lithosphere (land masses) and the biosphere (plants, animals, man and their habitat). The energy which drives this system comes from the sun and is intercepted by the earth and its atmosphere. This radiation interacts with clouds and air, land and sea, snow and ice, while the remainder is reflected back into space. Winds and ocean currents are generated by the forces set up by these complex interactions, which in turn are responsible for converting the sun's radiation into different energy forms and ultimately into long-wave terrestrial radiation which is emitted back into the outer space. ‘Weather’ is the end result of these complex activities when viewed on short time-scale, and ‘climate’, when the time-scale is long.

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During the life span of 4500 million years of the earth it has experienced several ice ages, each lasting several million years. In the intervening periods there were practically no polar ice caps. The most recent Ice Age started around 1·8 million years and still continues. During this period ice sheets over the poles and high mountains have extended and contracted in complicated patterns. Colder periods are termed ‘glacials’ and warmer ones ‘interglacials’. At the peak of the Last Glacial the ice sheets extended as far down as 40° N. in N. America and 52°30′ N. in Europe and, as a result of locking up of vast amounts of water in these ice sheets, the sea-level went down to 100 to 150 m below the present level.

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Due to various uncertainties involved the estimates for each interglacial vary from 5000 to 25000 years. The Last Glacial began around 120000 and reached its peak around 20000 B.P. and ended by 10000 B.P.—the onset of the Holocene [9.6]. Broadly speaking, the climatic cycles in the two hemispheres were in phase. It has been estimated that in *c.* 18000 B.P. the land-based ice sheets in the n. hemisphere reached a thickness of 3 km. In the s. hemisphere there was a corresponding increase in the sea ice. The surface waters cooled to a global average of 2·3 C. Corresponding to these glacial maxima, the tropics registered an intensely arid phase reflected in the lake levels of Africa. The early Holocene interglacial warming of the n. latitudes is matched by an increase of precipitation by 150% (over the 1931-60 mean) between 24° N. and 8° S. in Africa.

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The climatic changes are generally ascribed to the changes in the eccentricity of the earth’s orbit, obliquity of the axis and precession of the equinoxes, and to some extent to the ‘sun-spot cycle’. Recent searches on the marine sediments do reflect periodicities of 23000 years (corresponding to precession index), 42000 years (obliquity of the axis) and 100000 years (orbital eccentricity) which have given added support to Milankovitch’s original astronomical theories of climatic change. Considerable controversies however still exist in this field.

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Manifestations of climatic change are multifold. Changes in sea-level, extent of former ice sheets, lake levels, fluvial sediments of rivers, extent of deserts—all reflect changes in palaeoclimate. These are also manifested in the increase/decrease of cold- warmth-loving flora and fauna in the geological terrestrial and marine sediment records [9.8.1]. For example the cooling of the Pleistocene is marked by the disappearance of discosters and the appearance of cold-loving species like *Globorotalia truncatulinoides* and *Globorotalia menardii* complex (sinistral) at about 1·9 million years. There is a general correlation between the interglacial phases of the n. and the pluvial phases of the tropics. This can also be detected in the changes in the pollen record. For example the onset of deglaciation in Toshmaidan, Kashmir, is datable to *c.* 15000 B.P. and the advent of the early Holocene pluvial is marked in the pollen records of Rajasthan salt lakes at *c.* 10000 B.P. [7.4].

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Ericson, D.B., & Wollin, G., 1968, in *Science*, 162, pp. 1227-34 (for Pleistocene climates and deep-sea sediments). Frenzel, B., 1973, *Climatic Fluctuations of the Ice Ages*, London. Hays, J.D., Imbrie, J., & Shackleton, N.J., 1976, in *Science*, 194, pp. 1121-32 (for earth's orbit and ice ages) Lamb, H.H., 1971, in special issue of *Palaeoclimatology*, 10, 2-3, pp. 83-6. Lamb, H.H., 1972, *Climate: Present, Past & Future*, 1, London. *Report of a Committee on Climatic Change*, 1976, Australian Academy of Science, Canberra. Somayajulu, B.L.K., 1977, in Agrawal, D.P., & Pande, B.M., ed., *Ecology & Arch. of w. India*, pp. 5-16. Street, F.A., & Grove, A.T., 1976, in *Nature*, 261, pp. 385-90 (for late Quaternary lake-level fluctuations in Africa).—D.P. AGRAWAL

7.4 Palynology

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Palynology encompasses a wide range of studies based on the morphology and distribution of pollen and spores in space and time. These range from the study of pollen and spore fall-out on the face of the earth to the find of adulterants in different grades of honey, to the identification of allergenic substances in dust particulates, to the study of pollen morphology in relation to plant taxonomy and to the reconstruction of vegetational and environmental histories through pollen analysis of sedimentary deposits. In India palynology is known in practically all its diverse ramifications. It has contributed to Indian archaeology by way of the reconstruction of palaeo-environments of man over sections of the Quaternary Age [9.8]. The picture is far from complete but important gains have been made in some regions, notably Kashmir and Rajasthan.

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In Kashmir pollen studies of lower *karewa* lake deposits, dating from the Pliocene/early Pleistocene [9.8.2] times, have indicated significant changes of climate ranging from cool, moist temperate through cool dry temperate to cool, moist temperate conditions, but it has not yet been possible to relate these changes to any stratigraphically significant horizons indicating major glacial and interglacial periods [7.3].

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Most of the other pollen-analytical work has been confined to the Late Quaternary period. Here it has been demonstrated that after the last glacial in the Himalayas, corresponding to the Weichselian glacial in Europe, deglaciation was in progress at elevations as high as 3120 m (Toshmaidan) 14000 to 15000 years ago. Subsequently the vegetational altitudinal belts are shown to have moved up the mountain slopes progressively, indicating rise in temperatures. A period of temperatures higher than those of the present was reached some time during the middle post-glacial time. Subsequent changes in the vegetation indicate that the temperatures started to drop off before 3000 years ago. Phases of forest clearance resulting from human agricultural and other activities have been demonstrated both in the Kashmir valley (Haigam lake) and in the Kumaon Himalaya (Naukuchiya Tal) but in the absence of any ¹⁴C dates their chronology cannot yet be established. Small-scale forest clearance for agriculture, based on ¹⁴C-dated pollen profiles, has been shown to go back to at least 2000 B.C. (Khajjar lake) and large-scale clearance to periods onwards from A.D. 550 (Rewalsar lake) in Himachal Pradesh.

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In Rajasthan studies supported by absolute datings of three salt lakes—Sambhar, Didwana and Lunkaransar—in w. Rajasthan, and of one freshwater lake, Pushkar, in the Aravalli hills have brought out important changes in the environmental history of Rajasthan in relation to the development of human cultures in n.-w. India over the last 10000 years. The palaeo-environmental sequence is divided into five phases corresponding to five pollen zones as revised in Singh *et al.*, 1974.

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Phase I, before 8000 B.C., stratigraphically determined, is representative of severe arid environments under which the sand-dunes, now stabilized, are suggested to have been active. The period generally corresponds in time to at least the latter part of the Last Glacial in the Himalayas and is considered to have been extremely unsuitable for human habitation in Rajasthan. The conditions changed dramatically at the beginning of Phase II, 8000-7500 B.C., as shown by the infilling of large and small inland drainage basins with freshwater and the resulting deposition of lacustrine sediments. The date of this change coincides with the Late Weichselian/Flandrian boundary of w. Europe. The improvement in the availability of freshwater opened up possibilities of human migrations into the area. The vegetation comprised an openland steppe which was rich in grasses, *Artemisia* and sedges but poor in halophytes. *Artemisia, Typha angustata* (bull-rush), *Mimosa rubicaulis* and *Oldenlandia*, which now grow under areas of comparatively high average annual rainfall (above 500 mm), flourished in the semi-arid belt, while the first-two plant taxa had encroached even as far as the arid belt (100 to 250 mm mean annual rainfall), both suggesting that a general westward shift of the rainfall belts had taken place. Vegetation destruction through burning by man is suggested to have started together with the first occurrence of Cerealia-type pollen at about 7500 B.C. and continued thereafter throughout Phases III and IV. The increase in swamp vegetation and the intensification of vegetation cover inland together with the maxima of all mesophytic elements, including *Syzygium cuminii, jamun*, in Phase IV, c. 3000-1000 B.C., indicate an increase in rainfall. However there was a short relatively dry time about 1800-1500 B.C., and only a marginally wet period between 1500-1000 B.C., at Sambhar which coincides with the decline of the Indus culture [4.9] in n.-w. India. Between Phases IV and V there is a hiatus in the pollen preservation and at the same time there is stratigraphic evidence that the salt lakes started drying. At Pushkar there is evidence that the vegetation showed a marked change to a drier plant assemblage in the Aravallis. The onset of this aridity seems to have been widespread. The climate did not ameliorate until Phase V, early centuries A.D. to the present, at which time the RANG MAHAL culture the remains of which imply good water supply flourished in Rajasthan. The amelioration since the onset of aridity, however, has been small and has not led to any significant change in the overall climate of w. Rajasthan.

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Sharma, C., & Singh, G., 1972, in *Palaeobotanist*, 21, 2, pp. 144-62 (for vegetational history of Khajjar lake); in *ibid*., 21, 3, pp. 321-38 (for Rewalsar lake). Singh, G., 1963, in *ibid*., 12, 1, 73-108 (for post-glacial vegetational history of Kashmir); 1971, in *Arch. and Physical Anthropology in Oceania*, 6, 2, pp. 177-89 (for Indus civilization in the context of climate and ecology in n.-w. India). Singh, G., & Agrawal, D.P., 1976, in *Nature*, 260, p. 232 (for ¹⁴C evidence for deglaciation in n.-w. Himalayas). Singh, G., Joshi, R.D., Chopra, S.K., & Singh, A.B., 1974, in *Philosophical Transactions*, 267B, pp. 467-501 (for late Quaternary vegetation and climate of Rajasthan). Vishnu-Mittre, Gupte, H.P., & Robert, R., 1967, in *Current Science*, 36, 20, pp. 539-40 (for late Quaternary vegetation in Kumaon). Vishnu-Mittre, & Sharma, B.D., 1966, *Studies of Post-glacial Vegetational History from the Kashmir Valley, 1, Haigam Lake*. Vishnu-Mittre, Singh, G., & Saksena, K.M.S., 1962, in *Palaeobotanist*, 11, 1-2, pp. 92-5 (for pollen analysis in the lower *karewas*).—G. SINGH

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