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Thousands of years ago, the Earth’s magnetic field underwent a significant power surge over a part of the planet that 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 has found.
When scientists recently examined bricks from the third to first millennium BC in Mesopotamia – which included modern-day Iraq and parts of modern-day Syria, Iran and Turkey – they detected magnetic signatures in those from the first millennium, which indicates that the bricks. they were fired at a time when the Earth’s magnetic field was unusually strong. Stamps on the bricks that named Mesopotamian kings allowed researchers to confirm the time range for the magnetic spike.
Their findings were consistent with a known magnetic surge known as the “Iron Age Levantine Geomagnetic Anomaly,” which occurred between 1050 and 550 BC. It had previously been documented in artifacts from the Azores, Bulgaria and China using archaeological analysis — examining grains in ceramics 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 is very exciting that ancient artifacts from Mesopotamia help explain and record key events in Earth’s history such as fluctuations in the magnetic field,” said study co-author Mark Altaweel, professor of Near Eastern archeology and archaeological data science at University of Ireland, London. Institute of Archaeology.
“It shows why the preservation of Mesopotamia’s ancient heritage is important to science and humanity in general,” Altaweel told CNN in an email.
‘man-made rocks’
When an ancient artifact contains organic material, such as bone or wood, scientists can determine its age by radiocarbon dating, which compares decay rates preserved in carbon isotopes. But for inorganic artifacts — pottery or ceramic objects — archaeological analysis is needed to reveal their age, said lead study author Matthew Howland, an 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 a critical complement to radiocarbon dating, Howland told CNN.
“Archaeological dating can be applied to any type of magnetically sensitive material that is heated up,” Howland said. And its usefulness extends beyond archaeology.
“Geologists often use rock analysis to study the Earth’s magnetic fields, but in recent years when recent rocks cannot be studied because they haven’t had time to form yet, we need archaeological artifacts to use,” he said. . “We can think of mud bricks or pottery as man-made rocks to study the Earth’s magnetic fields.”
Before this new study, there was little concrete archaeological evidence from Mesopotamian artifacts from this time.
“That lack of data severely limits our ability to understand Earth’s magnetic field conditions in that region,” Howland said. It also meant that archaeologists were unable to accurately calculate the ages of many sites in Mesopotamia, “an extremely 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 metal at the Earth’s core. It prevents our atmosphere from being destroyed by solar winds as it blasts away from the sun. Although the magnetosphere has been a constant presence for billions of years, its strength waxes and wanes over time. (Magnetic field fluctuations do not directly affect human health, according to the US Geological Survey.)
Clay artifacts baked at high temperatures retain “fingerprints” of the Earth’s magnetism at the time in minerals such as iron oxide that have been affected by magnetism. Retrieving that fingerprint involves a series of magnetic experiments that repeatedly heat and cool the object, expose it to magnetic fields and then remove them. This process creates a new set of fingerprints, which are compared to the object’s original magnetic intensity.
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 is helping us understand what the Earth’s magnetic field is doing over time and it will also help determine the age of artifacts that would otherwise be impossible otherwise,” said Cauê S. Borlina, a postdoctoral fellow in the Department. Earth and planetary sciences at Johns Hopkins University… Borlina, who was not involved in the study, researches ancient and modern magnetic fields, and their influence on planet formation and habitability.
“More importantly, these high-resolution records are critical to understanding how magnetic spikes on the surface may connect to what’s happening inside Earth,” Borlina 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 data gap – it also revealed new clues about the period’s magnetic anomaly.
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 the stones showed that the magnetic field strengthened rapidly and strongly when the bricks were made. So the stamps on the bricks created an impression of a magnetic power surge that lasted for several decades.
“The next steps are to continue this work, apply it to more mud bricks from Mesopotamia and further improve the curve we can produce of the strength of the Earth’s magnetic field over time,” Howland said.
“But perhaps even more exciting is that archaeologists working on sites in Iraq and Syria can look at our data and apply the same techniques to undated artifacts,” he said. “This can help resolve many of the chronological debates that occur in the region, about the chronology of the kings.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine.
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