Title: Dating of Ancient Human Sites by the Palaeomagnetic Research Method
Abstract: The study concerns a new dating method way may well contribute to the establishment of chronology for anthropology and archaeology. It is based upon two kinds of phenomena, one of which is the secular variation in the geomagnetic declination and the geomagnetic inclination, and the other the thermo-remanent magnetization of baked earth. The baked earth is believed to maintain the residual magnetism, the direction of which coincides with that of the earth's magnetic field at the time of firing. So the declination and the inclination in ancient times are revealed by measuring the direction of the thermo-remanent magnetism of the baked earth in sites provided the baked earth has remained undistorted and undestroyed since it was baked. Then the aim of absolute dating is achieved by comparing the direction of the thermo-remanent magnetism of baked earth with the secular variation in the declination and the inclination in the past. For this purpose the standard scale of secular variation in these elements of the past must be established.One hundred and fourteen sets of samples of baked earth were collected from hearths, furnaces or kilns of prehistoric, protohistoric as well as historic Japan and measured on the direction of thermo-remanent magnetism. The secular variation curves of declination and inclination were estimated for the last 1700 years. The declination and inclination data odtained so far suggest that these two elements of geomagnetism have undergone secular variation since 6000 years B. P. within a limited range of magnitude, from 20°E to 30°W for declination and from 40°to 60°for inclination. It may be concluded that the secular variation must have been in a way periodic, the general feature of which may have resembled that obtained for the time range since 1700 years B. P. To establish the standard scale of the secular variation in the direction of geomagnetism in prehistoric times it is necessary to collect a number of coupled data, one of which is the direction of the thermo-remanent magnetism of baked earth and the other the absolute date obtained by the radiocarbon method on the materials contemporaneous with rethe baked earth. Up to now two such data have been obtained from remains of prehistoric Japan. Based upon these two data tentative variation curves of declination and inclination were estimated.At present, no single method is available which can provide completely correct and accurate dates for the past. The radiocarbon method which is thought to be the most reliable one is also subjected to conceivable inaccuracy. The two dating methods, by the radiocarbon assay and by the measurement of thermo-remanent magnetism, can be used to check each other and yield more highly reliable dates which may provide a more sound basis for studies in anthropology and archaeology.