Ancient bricks shed light on Earth's magnetic field anomalies 3,000 years ago

Ancient bricks shed light on Earth's magnetic field anomalies 3,000 years ago
by Sophie Jenkins
London, UK (SPX) Dec 19, 2023
Ancient bricks inscribed with the names of Mesopotamian kings have provided crucial insights into a significant anomaly in Earth's magnetic field that occurred around 3,000 years ago. This discovery, made by a team involving researchers from University College London (UCL), was recently detailed in a study published in the Proceedings of the National Academy of Sciences (PNAS).

The research revolves around the concept of archaeomagnetism, which involves studying the magnetic signatures recorded in archaeological materials. In this case, the focus was on iron oxide grains within ancient clay bricks. These grains captured changes in the Earth's magnetic field, allowing scientists to reconstruct these changes.

Professor Mark Altaweel of the UCL Institute of Archaeology, a co-author of the study, emphasized the importance of this technique, stating, "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. This work now helps create an important dating baseline that allows others to benefit from absolute dating using archaeomagnetism."

The team analyzed 32 clay bricks from Mesopotamian archaeological sites, corresponding to modern-day Iraq. These bricks bore the names of reigning kings, providing a historical context. The strength of Earth's magnetic field at the time of the bricks' creation was imprinted on the iron oxide minerals when they were first fired. The combination of the inscribed names and the measured magnetic strengths offered a historical map of the changes in the Earth's magnetic field strength.

This study has confirmed the existence of the "Levantine Iron Age geomagnetic Anomaly," a period of unusually strong magnetic field around 1050 to 550 BCE. This anomaly has been detected in regions as far-flung as China, Bulgaria, and the Azores, but data from the southern part of the Middle East had been limited until now.

Lead author Professor Matthew Howland of Wichita State University highlighted the broader implications of their findings, saying, "By comparing ancient artefacts 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."

To measure the magnetic strength, the researchers chipped tiny fragments from the bricks and used a magnetometer for precise measurements. This data not only aids in understanding changes in Earth's magnetic field but also offers a new tool for archaeologists to date ancient artefacts.

Additionally, this method can help historians more accurately determine the reigns of ancient kings. Although the duration and sequence of their reigns are known, precise starting years have been a subject of debate. The researchers found that their technique aligns with the "Low Chronology" understanding of these reigns.

The study also uncovered rapid changes in Earth's magnetic field during the reign of Nebuchadnezzar II (604 to 562 BCE), adding evidence to the hypothesis that the magnetic field can experience swift intensity spikes.

Co-author Professor Lisa Tauxe of the Scripps Institution of Oceanography (US) remarked on the significance of their findings: "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."

Research Report:Exploring Geomagnetic Variations in Ancient Mesopotamia: Archaeomagnetic Study of Inscribed Bricks from the 3rd-1st Millennia BCE