Ancient bricks reveal enigmas in Earth’s magnetic field

Ancient Mesopotamian bricks hold magnetic clues that will help archaeologists demystify the era.

A study published in Proceedings of the National Academy of Sciences has found that bricks bearing the names of Mesopotamian kings have been marked by changes in the Earth’s magnetic field.

The discovery could help to date the era more accurately, and provide a better insight into a geomagnetic anomaly that occurred between about 3,000 and 2,500 years ago.

“We often depend on dating methods such as radiocarbon dates to get a sense of chronology in ancient Mesopotamia,” says study co-author Professor Mark Altaweel, from the University College London Institute of Archaeology.

“However, some of the most common cultural remains, such as bricks and ceramics, cannot 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 UK, US and Israeli researchers looked at grains of iron oxide in 32 baked bricks. Each of these bricks hailed from ancient Mesopotamia, now modern-day Iraq, and each bore the name of the reigning king at the time of making. All in all, the bricks had the names of 12 Mesopotamian kings inscribed on them.

Brick with mesopotamian inscription on the front
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. Credit: Slemani Museum

The Earth’s magnetic field leaves a signature in magnetic compounds like iron oxide. Because the magnetic field changes in strength, these signatures change over time, and the researchers were able to spot this with a magnetometer.

The researchers combined the bricks’ magnetism with archaeological records of the kings, and created a “historical map” of magnetism in ancient Mesopotamia.

This map could be used to date other objects that aren’t handily labelled with a known king’s name.

“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,” says lead author Professor Matthew Howland, from Wichita State University, US.

They were also able to confirm the “Levantine Magnetic Anomaly”: a point of high magnetic intensity between 1050-550 BCE in modern-day Iraq.

Another interesting feature shown in 5 bricks was a swift magnetic change during the reign of Nebuchadnezzar II, which ran from 604-562 BCE.

“The geomagnetic field is one of the most enigmatic phenomena in earth sciences,” says co-author Professor Lisa Tauxe, from the Scripps Institution of Oceanography, US.

“The well-dated archaeological remains of the rich Mesopotamian cultures, especially bricks inscribed with names of specific kings, provides an unprecedented opportunity to study changes in the field strength in high time resolution, tracking changes that occurred over several decades or even less.”

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