An Encyclopaedia of Indian Archaeology v1.c12.s1: 7.1 Geochronology
An Encyclopaedia of Indian Archaeology v1.c12.s1
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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