Ancient Mesopotamian Bricks Record 3,000-Year-Old Geomagnetic Anomaly

A geomagnetic anomaly that occurred between 3,000 and 2,500 years ago has shed light on ancient Mesopotamia in a way that has never been explored before. Analysis of ancient bricks from Mesopotamia, specifically modern-day Iraq, point to a dramatic spike in the Earth’s magnetic field roughly 3,000 years ago. It is now the subject of a fascinating new study, which relies on archaeomagnetic techniques, i.e., extracting information about the strength and direction of the Earth’s magnetic field from ancient objects, and offers an alternative method of artifact dating.

Heating and Cooling: Firing the Bricks

These ancient Mesopotamian bricks, containing iron oxide, were employed to investigate the strength of the Earth's magnetic field during the firing period. Scientists systematically erased the ancient magnetic signature from small fragments of the bricks through a process of heating and cooling, according to the study published in The Proceedings of the Natural Academy of Sciences.

The bricks were then reheated, and the original magnetic field was replaced with one generated in the laboratory. This process enabled the researchers to establish a ratio between the object's magnetic charge in the past and under controlled laboratory conditions.

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Brick dates to the reign of Nebuchadnezzar II (ca. 604 to 562 BCE) based on the interpretation of the inscription. This object was looted from its original context before being acquired by the Slemani Museum and stored in that museum with agreement from the central government. (Image courtesy of the Slemani Museum)

Professor Mark Altaweel of University College London is studying the exceptional strength of the magnetic field in the Middle East around 3,000 years ago, known as the Levantine Iron Age Geomagnetic Anomaly: a point of high magnetic intensity between 1050-550 BC in modern-day Iraq.

“We often depend on dating methods such as radiocarbon dates to get a sense of chronology in ancient Mesopotamia. However, some of the most common cultural remains, such as bricks and ceramics, cannot typically be easily dated because they don’t contain organic material,” Altaweel said in a statement.

The findings revealed that these bricks were fired at a time when the Earth's magnetic field was more than one and a half times stronger than its present intensity. This time period corresponds to the Levantine Iron Age geomagnetic anomaly.

The anomaly, initially identified in 2009 by members of the same research team in a nearby region, was investigated using similar methods but on layers of rock material. History was literally baked into the bricks of cities through Iron Age Babylonia, reports The Hill.

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Another of the 32Mesopotamian clay bricks which bear names of 12 kings helped with the chronology. (MIT License)

Altaweel and his colleagues identified a set of 32 Mesopotamian clay bricks, each bearing inscriptions with the names of 12 different kings. It is presumed that these inscriptions were associated with the rulers during the time when the bricks were created. What makes these bricks particularly valuable for scientific analysis is the presence of iron oxide grains within them.

These grains have the unique ability to preserve the direction and strength of the magnetic field that existed when the bricks were initially fired. By examining the inscriptions and measuring the magnetic properties of the iron oxide grains, researchers gained insights into the Earth's magnetic field during the respective reigns of the kings.

Lead author Professor Matthew Howland of Wichita State University said, "By comparing ancient artifacts to what we know about ancient conditions of the magnetic field, we can estimate the dates of any artifacts that were heated up in ancient times."

Precise Dating Method: More than Just Carbon Dating

Carbon dating, which essentially measures the decay process from the moment of death, offers a highly accurate means of determining the time elapsed since the death of a being buried in a tomb or the cutting down of a tree used to fashion tools such as spear- or hoe-handles. This method plays a crucial role in pinpointing the chronological age of organic materials and contributes to the precision of archaeological dating.

However, despite the significance of the ruins of ancient cities, archaeologists face a significant challenge related to dating. The most dependable method for establishing the age of organic artifacts, ranging from cloth to wood to bones, involves tracking the systematic decay of radioactive carbon atoms within them, which is not always present.

Study co-author Professor Lisa Tauxe of the Scripps Institution of Oceanography explains the potential of the new approach:

"The geomagnetic field is one of the most enigmatic phenomena in Earth sciences. The well-dated archaeological remains of the rich Mesopotamian cultures, especially bricks inscribed with names of specific kings, provide an unprecedented opportunity to study changes in the field strength in high time resolution, tracking changes that occurred over several decades or even less."

“During…the first three millennia BC, you see the development of cities for the first time, the development of these incredibly complex societies like the Babylonians, and the development of agriculture for the first time in this region,” explained Howland in a Vice report. 

This approach offered a more precise chronological record compared to traditional methods like carbon dating, which often comes with uncertainties spanning decades or centuries. The length of a king's reign and the accuracy of historical timelines play crucial roles in enhancing the precision of this magnetic field-based dating method.

Traditionally, historical inscriptions have been used to corroborate archaeological research, but specifics are never clear, and can be hit and miss. A scientific method like this one provides a basis for future archaeologists to apply archaeomagnetic techniques to date previously un-dateable material at archaeological sites, like ceramics. This is because radiocarbon dating doesn’t work on ancient artifacts that don’t contain the C-14 carbon isotope.

In the future, even geologists desperate to understand the Earth’s geomagnetic behaviors can benefit from this method. Since scientists only began taking measurements from specific locations around the world 400 years ago, and only recently globally with the advent of satellites, the field can now be expanded across time and space.

Top image: Sulimaniya brick B318, part of the collection holding the signature of the geomagnetic anomaly.         Source: MIT License

By Sahir Pandey