An Encyclopaedia of Indian Archaeology v1.c10.s2.2

v1.c10.s2.2

For thousands of years clay has been used by man in making pottery, hearths, bricks and kilns. If the baked clay can be dated by reference to archaeological, ¹⁴C or thermoluminescent dating, one can make a record of geomagnetic variations in the past. Once such a secular variation curve is obtained, it can be used to date artefacts by fitting in their remanent magnetism in the known curve. The secular variation curve is different for different places in the world; hence separate magnetic curves have to be obtained for different regions. The necessary technique and criteria for reliable magnetic measurements for this purpose were established by Thellier and Thellier, 1959, and their first results showed that substantial variation had indeed occurred in the past. They found that in the Roman times the field intensity in France was some 60% higher than the present-day value.