Scientists have discovered new information about a mystery in Earth’s magnetic field from 3,000 years ago. They found this by studying old bricks from ancient Mesopotamia, which is now part of Iraq. The bricks were made long ago and have the names of kings from that time written on them.

This lets archaeologists know when each brick was made. The magnetic field of Earth changes over time in a special pattern. When the bricks were first baked in fire, tiny bits of iron in the clay recorded the strength of Earth’s magnetic field at that moment. Scientists can now measure the strength recorded in each brick’s iron bits.

By comparing the magnetic recordings to what we know about Earth’s magnetic field long ago, researchers found evidence of a time between 1050 and 550 BC when the field was unusually strong in Mesopotamia.

This period is called the Levantine Iron Age Geomagnetic Anomaly. Traces of it have been seen in places as far away as China, Bulgaria, and the Azores islands. But not much was known about it in the Middle East until now.

The team carefully chipped off tiny pieces from the broken surfaces of 32 clay bricks found in archaeological sites across ancient Mesopotamia.

Then they used a special tool called a magnetometer to precisely measure the magnetic recordings in the iron bits.

Comparing the magnetic strength to the writing on each brick let them map how Earth’s magnetic field changed over those kings’ reigns.

Knowing when each king ruled helps date the bricks more exactly. Some reign periods lasted decades, providing better precision than carbon dating which only gives results within a few hundred years.

This new technique can help archaeologists learn more accurate dates for artifacts and better understand disputed periods of ancient history.

The scientists also found evidence that Earth’s magnetic field may change quickly. Five bricks from the time of king Nebuchadnezzar II, between 604 and 562 BC, showed the field strength seemed to vary drastically over a relatively short time. This supports the idea that rapid spikes in field intensity are possible.

By recording Earth’s changing magnetic field through time, these ancient bricks provide a new dating tool. Measuring the magnetic recordings trapped long ago in heated objects like pottery or bricks can reveal their approximate age. This helps archaeologists learn more about rich ancient cultures like those of Mesopotamia.


University College London | Matthew D. Howland, Lisa Taupe, et al., Exploring geomagnetic variations in ancient mesopotamia: Archaeomagnetic study of inscribed bricks from the 3rd–1st millennia BCE. PNAS, December 18, 2023, 120 (52) e2313361120.

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