Mesopotamian bricks reveal anomaly in Earth’s magnetic field 3,000 years ago

New research involving UCL researchers has uncovered important insights into a puzzling anomaly in Earth’s magnetic field 3,000 years ago, thanks to ancient bricks inscribed with the names of Mesopotamian kings.

The research describes how changes in the Earth’s magnetic field left a distinct imprint on iron oxide grains within these clay bricks, allowing scientists to reconstruct these changes based on the kings’ inscriptions.

Unveiling Earth’s magnetic field anomaly

This research utilizes a field known as “archaeomagnetism,” which seeks magnetic field signatures in archaeological artifacts. The team hopes that by employing this method, they can enhance our understanding of Earth’s magnetic field history while also providing more accurate dating of artifacts that were previously difficult to determine.

Co-author Professor Mark Altaweel of UCL Institute of Archaeology explains the significance of this work. He said, “We often rely on dating methods like radiocarbon dating to establish chronology in ancient Mesopotamia. However, common cultural remains such as bricks and ceramics cannot be easily dated because they lack organic material. This work establishes a crucial dating baseline for others to benefit from absolute dating using archaeomagnetism.”

Over time, the Earth’s magnetic field undergoes weakening and strengthening, leaving a distinct signature on minerals that are sensitive to magnetic fields.

In this study, the team examined the latent magnetic signatures in iron oxide grains found in 32 clay bricks from various archaeological sites throughout Mesopotamia, which corresponds to present-day Iraq. These minerals acquired the strength of the Earth’s magnetic field when the bricks were first fired thousands of years ago.

Mapping the Earth’s magnetic field

Each brick was inscribed with the name of a specific king, enabling archaeologists to estimate the likely timespan during which the bricks were made. By combining the imprinted names and the measured magnetic strength of the iron oxide grains, the researchers constructed a historical map of the changes in the Earth’s magnetic field.

The study ultimately confirmed the existence of the “Levantine Iron Age geomagnetic Anomaly.” This anomaly denotes a period from approximately 1050 to 550 BCE when the Earth’s magnetic field was exceptionally strong in the region of modern-day Iraq for unknown reasons.

Evidence of this anomaly has been detected as far as China, Bulgaria, and the Azores, but data from the southern part of the Middle East itself have been scarce.

Lead author Professor Matthew Howland of Wichita State University explains how ancient artifacts can be dated using this magnetic insight. He said, “By comparing ancient artifacts to our knowledge of the magnetic conditions in ancient times, we can estimate the dates when these items were heated up.”

Archaeomagnetic dating: Advantages and precision

To measure the iron oxide grains, the team delicately chipped tiny fragments from the broken faces of the bricks and used a magnetometer for precise measurements. Aside from shedding light on Earth’s magnetic field changes, this data provides archaeologists with a valuable tool for dating ancient artifacts.

The magnetic strength of iron oxide grains embedded within fired items can be measured and compared to the known strengths of past Earth magnetic fields. This approach offers better resolution than radiocarbon dating, which only provides a date range within a few hundred years, as the reigns of kings often lasted from years to decades.

Moreover, archaeomagnetic dating helps to pinpoint the reigns of ancient kings with greater precision. While the length and order of their reigns are well-known, conflicting historical records have led to disagreements among archaeologists regarding the exact years of their reigns. The researchers found that their technique aligns with the archaeological understanding of the “Low Chronology” of these kings.

Rapid magnetic field changes and anomalies

The study also revealed that during the reign of Nebuchadnezzar II from 604 to 562 BCE, the Earth’s magnetic field appeared to undergo rapid and substantial changes in just a short period. This finding adds weight to the hypothesis that intense spikes in magnetic field strength can occur.

Co-author Professor Lisa Tauxe of the Scripps Institution of Oceanography (US) emphasizes the unique opportunity provided by well-dated archaeological remains from Mesopotamian cultures.

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

The research conducted with funding from the U.S.-Israel Binational Science Foundation paves the way for a deeper understanding of Earth’s magnetic field history and offers a new tool for more precise artifact dating.

In summary, by examining iron oxide grains within ancient bricks and correlating them with the inscribed names of Mesopotamian kings, scientists have gained invaluable insights into the mysterious magnetic field anomaly from 3,000 years ago.

This study demonstrates the power of archaeomagnetism in unraveling Earth’s ancient secrets and sheds light on the reigns of ancient kings, providing a more accurate timeline of their rule.

The full study was published in Proceedings of the National Academy of Sciences.

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