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Thousands of years ago, Earth’s magnetic field suffered a significant power surge in a part of the planet that included the ancient kingdom of Mesopotamia. People probably didn’t even notice the fluctuation at the time, but new research has revealed that signs of the anomaly, including previously unknown details, were preserved in the adobe bricks they fired.
Scientists have recently discovered that B.C. They were fired at a time when the Earth’s magnetic field was unusually strong. Stamps bearing the names of Mesopotamian kings on the bricks allowed the researchers to confirm the time period of the magnetic spike.
Their findings corresponded to a known magnetic fluctuation called the “Levantine Iron Age geomagnetic Anomaly” that occurred between 1050 and 550 BC. This had previously been documented using archeomagnetic analysis in artifacts from the Azores, Bulgaria and China, scientists reported Dec. 18 in the journal Proceedings of the National Academy of Sciences; He obtained clues about the Earth’s magnetic activity by examining grains in pottery and ceramic archaeological objects.
“It’s really exciting that ancient artifacts from Mesopotamia help explain and record important events in Earth 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 College London. Institute of Archaeology.
“This demonstrates why preserving the ancient heritage of Mesopotamia is important for science and humanity more broadly,” Altaweel told CNN in an email.
‘Man-made rocks’
When an ancient artifact contains organic material such as bone or wood, scientists can determine how old the artifact is through radiocarbon dating, which compares decay rates preserved in carbon isotopes. But archaeomagnetic analysis is needed to reveal the ages of inorganic artifacts (pottery or ceramic objects), said the study’s lead author, Matthew Howland, an assistant professor in the department of anthropology at Wichita State University in Kansas.
Since pottery is the most common type of artifact at archaeological sites around the world, the technique is a vital complement to radiocarbon dating, Howland told CNN.
“Archaeomagnetic dating can be applied to any magnetically sensitive material that is heated,” Howland said. And its usefulness extends beyond archaeology.
“Geologists often use the analysis of rocks to study Earth’s magnetic fields, but more recently, when it is not possible to study very young rocks because they have not yet had time to form, we need to use archaeological artifacts,” he said. . “We can think of adobe or pottery as man-made rocks used to study Earth’s magnetic fields.”
Before this new study, there was little definitive archeomagnetic evidence from Mesopotamian artifacts dating to this period.
“The lack of data there has really limited our ability to understand the conditions of the Earth’s magnetic field in that region,” Howland said. This 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 produced by the powerful churning of molten metals in the Earth’s core. It prevents our atmosphere from being stripped away by solar winds from the sun. Although the magnetosphere has existed for billions of years, its strength waxes and wanes over time. (According to the US Geological Survey, human health is not directly affected by magnetic field fluctuations.)
Clay artefacts fired at high temperatures preserve the “fingerprint” of Earth magnetism at the time in minerals such as iron oxide that are affected by magnetism. Taking this fingerprint involves a series of magnetic experiments that repeatedly heat and cool the object, exposing it to magnetic fields and then removing them. This process creates a set of new fingerprints that are compared to the original magnetic density of the object.
Scientists can then match the object to a specific period of activity in the Earth’s magnetic field.
“Overall, this is an exciting study because it helps us understand what the Earth’s magnetic field does over time, and it will also help determine the age of artifacts that would otherwise be impossible,” said Cauê S. Borlina, a postdoctoral researcher in the department. Earth and planetary sciences at Johns Hopkins University. Borlina, who was not involved in the research, conducts research on ancient and modern magnetic fields and their effects on planet formation and habitability.
“Most importantly, these high-resolution records are crucial to understanding how surface magnetic spikes might connect to what’s happening on 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, but also revealed new clues about the magnetic anomaly of that period.
Five of the 32 stones the researchers sampled date them back to World War II, between 604 and 562 BC. There were stamps connecting it to the period of Nebuchadnezzar. Measurements of magnetism in the stones showed that the magnetic field strengthened rapidly and intensely as the bricks were made. The imprints on the bricks therefore constituted a snapshot of the magnetic power fluctuation that spanned only a few decades.
“The next steps will be to continue this work, apply it to more adobe bricks in Mesopotamia, and over time further refine the curve we can produce of the intensity of the Earth’s magnetic field,” Howland said.
“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 artifacts,” he added. “This could help resolve many chronological debates occurring 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 magazines.
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