When objects containing magnetic minerals burn at a very high temperature, those minerals are re-magnetized and therefore record the direction and the magnitude of the field in that precise moment. Artifacts like pottery, bricks and tiles, which are fired in furnaces, ovens and kilns, can all provide these records. However, as precise as their dating can be, it usually spans of at least a few decades. On the contrary, if documented by historical records, destruction lawyers can be pinned down to a very specific moment – in the case of Jerusalem in 586 almost to the date - providing a unique opportunity.According to the Bible (2 Kings 25:3-4), the wall of Jerusalem was breached on the ninth day of the fourth month. This is the basis for the holy day the Ninth of Av. Traditionally other days of the disaster for the Jewish people took place on the same date, including the fall of Jerusalem to the Romans in 70 CE and the fall of Betar, the center of the Bar Kokhba Revolt, in 135 CE.
The PLOS One article where this research is published is: The Earth’s magnetic field in Jerusalem during the Babylonian destruction: A unique reference for field behavior and an anchor for archaeomagnetic dating (Yoav Vaknin , Ron Shaar, Yuval Gadot, Yiftah Shalev, Oded Lipschits, Erez Ben-Yosef).
Paleomagnetic analysis of archaeological materials is crucial for understanding the behavior of the geomagnetic field in the past. As it is often difficult to accurately date the acquisition of magnetic information recorded in archaeological materials, large age uncertainties and discrepancies are common in archaeomagnetic datasets, limiting the ability to use these data for geomagnetic modeling and archaeomagnetic dating. Here we present an accurately dated reconstruction of the intensity and direction of the field in Jerusalem in August, 586 BCE, the date of the city’s destruction by fire by the Babylonian army, which marks the end of the Iron Age in the Levant. We analyzed 54 floor segments, of unprecedented construction quality, unearthed within a large monumental structure that had served as an elite or public building and collapsed during the conflagration. From the reconstructed paleomagnetic directions, we conclude that the tilted floor segments had originally been part of the floor of the second story of the building and cooled after they had collapsed. This firmly connects the time of the magnetic acquisition to the date of the destruction. The relatively high field intensity, corresponding to virtual axial dipole moment (VADM) of 148.9 ± 3.9 ZAm2, accompanied by a geocentric axial dipole (GAD) inclination and a positive declination of 8.3°, suggests instability of the field during the 6th century BCE and redefines the duration of the Levantine Iron Age Anomaly. The narrow dating of the geomagnetic reconstruction enabled us to constrain the age of other Iron Age finds and resolve a long archaeological and historical discussion regarding the role and dating of royal Judean stamped jar handles. This demonstrates how archaeomagnetic data derived from historically-dated destructions can serve as an anchor for archaeomagnetic dating and its particular potency for periods in which radiocarbon is not adequate for high resolution dating.
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