Ancient bricks reveal new evidence about a massive anomaly in Earth's magnetic field

Matthew D. Howland

These ancient clay bricks are stamped with an inscription mentioning the Mesopotamian king Ekun-Dire. The researchers sampled them for their study and are excited about how such artifacts could help us study Earth's magnetic fields.

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Thousands of years ago, Earth magnetic field It underwent a major energy influx on the part of the planet that included the ancient kingdom of Mesopotamia. People at the time probably never noticed the fluctuations, but signs of anomalies, including previously unknown details, were preserved in the clay bricks they baked, a new study has found.

When scientists recently examined bricks dating back to the third to first millennium BC in Mesopotamia – which… It included present-day Iraq and parts of what is now Syria, Iran, and Turkey – they discovered magnetic signatures in those dating back to the first millennium, suggesting that the bricks were fired at a time when the Earth's magnetic field was unusually strong. Stamps on the bricks bearing the names of Mesopotamian kings enabled researchers to confirm the time scale of the magnetic rise.

Their findings are consistent with a known magnetic surge called the Levantine Iron Age geomagnetic anomaly, which occurred between 1050 and 550 BC. It has been previously documented in artifacts from the Azores, Bulgaria and China using archaeological magnetic analysis — examining grains in pottery and ceramic artifacts for clues about the Earth's magnetic activity, the scientists reported Dec. 18 in the journal . Proceedings of the National Academy of Sciences.

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“It is really exciting that ancient artifacts from Mesopotamia can help explain and record key events in Earth's history such as fluctuations in the magnetic field,” said the study's co-author. Mark TawilProfessor of Near Eastern Archeology and Archaeological Data Science at the Institute of Archaeology at University College London.

“This demonstrates the importance of preserving the ancient heritage of Mesopotamia for science and humanity more broadly,” Al-Tawil told CNN in an email.

When an ancient artifact contains organic material, such as bone or wood, scientists can tell its age through radiocarbon dating, which compares the percentages of decay preserved in carbon isotopes. But for inorganic artifacts — such as pottery or ceramics — archaeological magnetic analysis is necessary to reveal their age, said the study's lead author. Matthew Howlandassistant professor in the Department of Anthropology at Wichita State University in Kansas.

Howland told CNN that pottery is the most common type of artifact in archaeological sites around the world, and this technique is a vital complement to radiocarbon dating.

“Archaeomagnetic dating can be applied to any type of magnetically sensitive material that has been heated,” Howland said. Its usefulness extends beyond archaeology.

“Geologists often use rock analysis to study the Earth's magnetic fields, but recently when there is no possibility to study very young rocks because they have not had enough time to form yet, we need to use archaeological artifacts,” he said. . “We can think of adobe or pottery as man-made rocks to study the Earth's magnetic fields.”

Before this new study, there was little accurate magnetic evidence from Mesopotamian artifacts dating to this time.

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“The lack of data there has really limited our ability to understand the Earth's magnetic field conditions in that region,” Howland said. It also means that archaeologists have been unable to accurately calculate the ages of many sites in Mesopotamia, “a very important region in global archaeology.”

The Earth is surrounded by a magnetosphere – an invisible bubble of magnetism created by the powerful churning of molten metals in the Earth's core. It prevents our atmosphere from being exposed to the solar winds that blow on it from the sun. While the magnetosphere has been around continuously for billions of years, its strength waxes and wanes over time. (Human health is not directly affected by magnetic field fluctuations, according to… US Geological Survey.)

Clay artifacts that were baked at high temperatures retain the “imprint” of the Earth's magnetism at that time in minerals such as iron oxide that are affected by magnetism. Recovering a fingerprint involves a series of magnetic experiments that repeatedly heat and cool the object, expose it to magnetic fields and then remove it. This process creates a series of new fingerprints, which are compared to the object's original magnetic density.

Scientists can then match the object to a specific period of activity in the Earth's magnetic field.

“Overall, this is exciting work because it helps us understand what the Earth's magnetic field does over time, and will also help determine the age of artifacts that would otherwise be impossible,” he said. KS Burlina, a postdoctoral fellow in the Department of Earth and Planetary Sciences at Johns Hopkins University. Burlina, who was not involved in the study, is conducting research on ancient and modern magnetic fields and their impact on planetary formation and habitability.

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“More importantly, these high-resolution records are essential to understanding how magnetic spikes on the surface might relate to what's happening inside the Earth,” Burlina told CNN in an email. “Especially in the outer core where the Earth's magnetic field is generated.”

The new analysis not only filled an important gap in the data, but also revealed new evidence about the magnetic anomalies of the period.

Of the 32 stones sampled by the researchers, five bore stamps linking them to the reign of Nebuchadnezzar II, between 604 and 562 BC. Measurements of magnetism in stones have shown that the magnetic field strengthens rapidly and intensely when making bricks. Thus, the stamps on the bricks created a snapshot of the flow of magnetic energy that spanned only a few decades.

“The next steps are to continue this work, apply it to more clay bricks from Mesopotamia and further improve the curve we can produce for the Earth's magnetic field intensity over time,” Howland said.

“But perhaps what's even more exciting is that archaeologists working at sites in Iraq and Syria can look at our data and apply the same techniques to undated artifacts,” he added. “This could help resolve a lot of historical debates that happen in the region, about the chronology of kings.”

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works.

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