Researchers from Tel Aviv University, the Hebrew University of Jerusalem, and the Israel Antiquities Authority were able to measure the Earth's magnetic field in Jerusalem in 586 BCE-- the time when the city was destroyed by the Babylonians. The groundbreaking study widened the understanding of the ruins of Jerusalem and shaped a contribution by Jewish people's long memory to uncover traces of the planet's history.
According to lead author Yoav Vaknin, the study breaks new grounds in understanding the devastation of Jerusalem and also gives key insights in a scientific discipline that has vast significance in many contemporary aspects of life-- from navigation systems to environmental concerns.
One famous two-story building, just a few steps from the Temple Mount, was set on fire and collapsed. Over 2 600 years later, its carbonized beams and stones revealed in the Givati parking lot excavation at the City of David National Park depict a clear testimony of those times, whose terrible events are described in the Bible.
The last chapter of the book of II Kings says: "By the ninth day [of the fourth month] the famine had become acute in the city; there was no food left for the common people. Then [the wall of] the city was breached. All the soldiers [left the city] by night through the gate between the double walls.
"On the seventh day of the fifth month-- that was the nineteenth year of King Nebuchadnezzar of Babylon-- Nebuzaradan, the chief of the guards, an officer of the king of Babylon, came to Jerusalem. He burned the House of the LORD, the king’s palace, and all the houses of Jerusalem; he burned down the house of every notable person."
Among the most remarkable remains were some fragments of a sophisticated plaster floor that have been left in the same position for thousands of years. The pieces proved to be crucial for measuring the strength and direction of the Earth's magnetic field in those exact moments.
"Even though my Ph.D. is in archaeology, this is an interdisciplinary research between archaeology and live sciences," said Vaknin.
"One of the goals of their lab is to understand how the magnetic field behaved in the past before direct measurement began some 400 years ago at the initiative of the captain of a British ship."
Over time, data gathering became vaster and more accurate. In the 19th century, Mathematician Carl Friederich Gauss developed a system to measure the intensity of the phenomenon. Today, the most precise information is provided by satellites, which are not impacted by any human interference.
While the direction has been linked to the geographic north in modern history, the magnetic field is known to have been entirely neutral or pointing south in the past. Since it also represents an important factor to screen the planet from hazardous solar radiation, the researchers worry about what might happen if such changes should happen again.
"Recently we have seen many instances in which live sciences are giving a contribution to archaeology, but in this case also the opposite is true," Vaknin pointed out.
The team decided to focus on the issue of the Earth's magnetic field in archaeological layers, resulting from massive devastations. When objects containing magnetic minerals burn at a very hot temperature, those minerals are re-magnetized and thus, record the direction and the magnitude of the field in that exact moment.
Artifacts such as pottery, tiles, and bricks-- fired in furnaces, kilns, and ovens-- can provide these records. However, as accurate as dating can be, it usually spans a few decades, at least. In contrast, if documented by historical records, destruction lawyers can be pinpointed to a very particular moment-- in the case of Jerusalem in 586 BCE almost to the date.
"The focus of my research was the Iron Age, which in Israel goes from around 1200 to 586 BCE. In the beginning, I tried to focus on a different archaeological site where they had uncovered traces of the Babylonian destruction also located in the City of David but I was not able to carry on the measurements effectively. I was then suggested trying just across the street," said Vaknin.
The preliminary results seemed promising, until a few months later, the archaeologists reached the flood of the building and the findings confirmed the dating and provided new insights.
"We dated the destruction of the structure to 586 BCE - the destruction of Jerusalem by the Babylonians, based on smashed pottery vessels typical of the end of the First Temple period, found on the floor. Apart from the broken utensils, we found signs of burning and large quantities of ashes," said Dr. Yiftah Shalev of the IAA and Gadot of TAU.
"Measuring magnetic data from a floor burned thousands of years ago is no trivial matter," said Dr. Ron Shaar, the director of the Paleomagnetic Lab at the Hebrew University.
"We had to characterize the magnetic particles, understand how the magnetic data was coded in the material, and develop measuring techniques enabling us to read this data. Nature hasn't made life easy for us. Thus a significant part of the analytical work we do at the paleomagnetic lab is investigating the magnetic properties of the archaeological materials."
"Fortunately, in this particular study, Yoav was able to decipher nature's magnetic code and give us important information from several angles: historic, archeological, and geomagnetic."
The team is working on similar research on destruction lawyers from various periods in other sites, like the one caused by the Assyrian conquest in the 8th century.
"We are building the curve from a lot of data and the idea is that the destruction lawyers which are very precisely dated are the chronological anchors for all this information," Vaknin concluded.
"The Earth’s magnetic field in Jerusalem during the Babylonian destruction: A unique reference for field behavior and an anchor for archaeomagnetic dating" - Vaknin, Y. et al. - PLOS One - https://doi.org/10.1371/journal.pone.0237029
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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