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Thousands of years ago, Earth’s magnetic field experienced a significant surge across a portion of the planet, which included the ancient kingdom of Mesopotamia. People at the time probably didn’t even notice the fluctuation, but signs of the anomaly, including previously unknown details, were preserved in the mud bricks they baked, new research shows.
When scientists recently examined stones dating from the third to first millennium BC in Mesopotamia – which included modern-day Iraq and parts of what is now Syria, Iran and Turkey – they discovered magnetic signatures in those from the first millennium, indicating that the stones were fired at a time when the Earth’s magnetic field was unusually strong. Stamps on the stones with the names of Mesopotamian kings allowed researchers to confirm the time range for the magnetic peak.
Their findings matched a well-known magnetic wave, the ‘Levantine Iron Age geomagnetic anomaly’, which occurred between 1050 and 550 BC. It had previously been documented in artifacts from the Azores, Bulgaria and China using archaeomagnetic analysis — examining grains in pottery and ceramic archaeological objects for clues about Earth’s magnetic activity, scientists reported Dec. 18 in the journal Proceedings of the National Academy of Sciences.
“It’s really exciting that ancient artifacts from Mesopotamia help explain and record important events in Earth’s history, such as fluctuations in the magnetic field,” said co-author Mark Altawee, professor of Near Eastern archeology and archaeological data science at University College London. Institute of Archaeology.
“It shows why preserving Mesopotamia’s ancient heritage is important for science and humanity more broadly,” Altawee told CNN in an email.
‘Man-made rocks’
When an ancient artifact contains organic material, such as bone or wood, scientists can learn how old it is through radiocarbon dating, which compares the ratios of decay preserved in carbon isotopes. But for inorganic artifacts — pottery or ceramic objects — archaeomagnetic analysis is needed to reveal their age, said lead study author Matthew Howland, assistant professor in the department of anthropology at Wichita State University in Kansas.
Because pottery is the most common type of artifact at archaeological sites around the world, this technique is an essential complement to radiocarbon dating, Howland told CNN.
“Archeomagnetic dating can be applied to all types of magnetically sensitive materials that have been heated,” says Howland. And its usefulness extends beyond archaeology.
“Geologists often use analyzes of rocks to study the Earth’s magnetic fields, but in more recent times, when there is no opportunity to study very recent rocks because they have not yet had time to form, we must use archaeological artifacts “, he said. . “We can think of mud bricks or pottery as man-made rocks to study Earth’s magnetic fields.”
Before this new study, there was little accurate archaeomagnetic evidence of Mesopotamian artifacts from this era.
“The lack of data there limits our ability to understand the conditions of Earth’s magnetic field in that area,” Howland said. It also meant that archaeologists could not accurately calculate the age of many sites in Mesopotamia, ‘an incredibly important region in world archaeology’.
Magnetic attraction
The Earth is surrounded by a magnetosphere: an invisible bubble of magnetism generated by the powerful churning of molten metals in the Earth’s core. It prevents our atmosphere from being swept away by solar winds that blow it away from the sun. Although the magnetosphere has been constant for billions of years, its strength waxes and wanes over time. (According to the US Geological Survey, human health is not directly affected by fluctuations in the magnetic field.)
Clay artefacts fired at high temperatures retain a ‘fingerprint’ of the Earth’s magnetism at the time in minerals such as iron oxide that were affected by magnetism. Retrieving that fingerprint involves a series of magnetic experiments in which the object is repeatedly heated and cooled, exposed to magnetic fields, and then removed. This process creates a series of new fingerprints, which are compared to the original magnetic intensity of the object.
Scientists can then link the object to a specific period of activity in Earth’s magnetic field.
“Overall, this is exciting work because it helps us understand what Earth’s magnetic field does over time and also helps determine the age of artifacts that would otherwise be impossible,” says Cauê S Borlina, a postdoctoral researcher in the Department of Earth and Planetary Sciences at Johns Hopkins University. Borlina, who was not involved in the research, conducts research into ancient and modern magnetic fields and their impact on the formation and habitability of planets.
“Most importantly, these high-resolution images are crucial for understanding how magnetic spikes on the surface can be related to what is happening inside the Earth,” Borlina told CNN in an email. “Especially in the outer core, where Earth’s magnetic field is generated.”
The new analysis not only filled an important data gap, but also revealed new clues about the magnetic anomaly of that period.
Of the 32 stones the researchers sampled, five bore a stamp linking them to the reign of Nebuchadnezzar II, between 604 and 562 BC. Measurements of the magnetism in the stones showed that the magnetic field strengthened rapidly and intensely when the stones were made. The stamps on the stones therefore created a snapshot of a magnetic current surge that lasted only a few decades.
“The next steps are to continue this work, apply it to more mudstones from Mesopotamia and further improve the curve we can produce over time of the intensity of Earth’s magnetic field,” said Howland.
“But perhaps 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 artefacts,” he added. “This could help resolve many of the chronological debates taking place in the region about the chronology of kings.”
Mindy Weisberger is a science writer and media producer whose work has appeared in the magazines LiveScience, Scientific American, and How It Works.
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