Archeomagnetism of Metallurgical Slag Deposits in Israel and Jordan: Constraints for Secular Variation Models for the last 7000 Years

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

The origin of Earth's magnetic field and its past behavior remain among the long standing problems in the Earth sciences. Paleomagnetism, the study of the ancient geomagnetic field, is one of the more useful sources of information on past processes in the deep interior of the planet. Enormous effort over many decades has produced a huge amount of data for the ancient geomagnetic field. These data have been incorporated into increasingly sophisticated models of the geomagnetic field. Apart from placing the recent behavior of the geomagnetic field into some sort of historical context, its behavior over the Holocene is also of interest to a wide variety of investigators including archaeologists, historians, and paleoclimate researchers. The geomagnetic field is one of the primary controls of radiocarbon production hence strongly effects the radiocarbon calibration curves. Sorting out field variations are key to interpretations of past solar activity. Moreover, an accurate model of geomagnetic field variations could ultimately provide the long awaited time scale based on secular variation. To further these disparate goals, we will combine expertise from archaeology and paleomagnetism to obtain a new paleointensity data from well dated material from copper mining slags in Israel and Jordan. The symbiosis of archaeology and archeomagnetism has a long and distinguished record. The study of the ancient geomagnetic field requires materials that retain a record of the magnetic field vector prior to human calendrical measurements that can be retrieved and calibrated in the laboratory. In turn, comparison of the magnetic vector with previously established variations of the magnetic field can provide age constraints on poorly dated archeological material. One of the major drawbacks with the current database for the Earth's magnetic field is the relative lack of data concerning the strength of the vector. This is because it is quite difficult to obtain suitable material that both behaves well during the laboratory experiment and also can be accurately dated with radiometric methods. Advances in the laboratory experiment and recognition of quickly cooled ancient metallurgical slag as a potentially ideal material for paleointensity study suggest that our understanding of the changes in the Earth's magnetic field over time can be much improved. In turn the improved geomagnetic field model could be applied to the problem of dating archaeo-metallurgical slag deposits that lack precise archeological context (e.g., material collected from the surface). This project involves collecting new material from ancient sites of copper metal production primarily in Jordan spanning the 4th through 1st millennia BCE. The archaeometallurgcal material will be collected from active archeological excavations in the summer of 2007 and analyzed for both radiocarbon age and the ancient magnetic field strength. The data assembled under this grant will contribute to our general knowledge of paleosecular variation and impact the broader issues of radiocarbon calibration curves, variability of solar activity, secular variation time scales and so on. Moreover, this proposal will enhance interdisciplinary research between geophysics and archeology Including provide funding for Erez ben Yosef who is working with both P.I.s at UCSD in an interdisciplenary study combining geophysics and archeology. He will become expert in both fields.