Cuneiform Tablets in Mesopotamia Reveal the Strength of the Ancient Geomagnetic Field

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You can also read this article in Turkish. Mezopotamya'daki Çivi Yazılı Tuğlalar Eski Jeomanyetik Alanın Gücünü Açıklıyor

Professor Altaweel, a co-author of the paper published in the Proceedings of the National Academy of Sciences, said:

"To gain a chronological understanding of ancient Mesopotamia, we generally rely on dating methods such as radiocarbon."

"However, the most common cultural remains, such as bricks and ceramics, are often difficult to date because they usually do not contain organic material."

"This work is now helping to create an important dating framework that will allow others to benefit from absolute dating using paleomagnetism."

The Earth's magnetic field weakens and strengthens over time, and these changes leave a distinct signature on magnetically sensitive heated minerals.

The authors of the study analyzed the hidden magnetic signature of iron oxide minerals in 32 clay bricks from archaeological sites in Mesopotamia, which corresponds to modern Iraq.

The strength of the magnetic field was imprinted on the minerals when they were first fired by brickmakers thousands of years ago.

Each brick was inscribed with the name of the reigning monarch at the time of its construction, and archaeologists had dated them with probable time ranges.

Together, the written name and the measured magnetic strength of the iron oxide grains provided a historical map of changes in the Earth's magnetic field strength.

The researchers were able to confirm the existence of the Levant Iron Age geomagnetic anomaly, a period between 1050 and 550 BCE when the Earth's magnetic field was unusually strong in the vicinity of modern Iraq for reasons that are not fully understood.

Evidence of the anomaly had been detected as far away as China, Bulgaria, and the Azores, but data from the southern part of the Middle East itself was scarce.

"By comparing artifacts to what we know about past conditions of the magnetic field, we can estimate the date of any heated object in ancient times," said Professor Matthew Howland, lead author of the study and a professor at Wichita State University.

The scientists carefully chipped tiny pieces from the broken faces of the bricks to measure the iron oxide grains, and used a magnetometer to precisely measure the particles.

This data also provides a new tool for archaeologists to help date some ancient artifacts by mapping changes in the Earth's magnetic field over time.

The magnetic strength of iron oxide grains embedded in fired objects can be measured and then matched to known strengths of the Earth's historical magnetic field.

The reigns of kings lasted for years or even decades, offering much better resolution than radiocarbon dating, which can only date an object to within a few hundred years.

The team also found that five samples taken during the reign of Nebuchadnezzar II, between 604-562 BCE, revealed that the Earth's magnetic field changed dramatically in a relatively short period of time, adding evidence to the hypothesis that rapid increases in intensity are possible.

"The geomagnetic field is one of the most mysterious phenomena in the Earth sciences," said Professor Lisa Tauxe, a co-author of the paper and a researcher at the Scripps Institution of Oceanography.

"The well-dated archaeological remains of the rich Mesopotamian cultures, especially bricks inscribed with the names of specific kings, offer a unique opportunity to study changes in field strength with high time resolution, to track changes that occurred on timescales of decades or even a few years."

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