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Thousands of years ago, Earth’s magnetic field experienced a major surge of energy in 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, according to new research.
When scientists recently examined bricks dating from the third to first millennium BC in Mesopotamia (which encompassed modern-day Iraq and parts of modern-day Syria, Iran, and Turkey), they detected magnetic signatures in those from the first millennium, indicating that the bricks were fired at a time when the Earth’s magnetic field was unusually strong. Seals on bricks naming Mesopotamian kings allowed researchers to confirm the time range of the magnetic peak.
Their findings corresponded to a known magnetic surge called the “Levantine Iron Age geomagnetic anomaly”, which took place between 1050 and 550 BC. It had previously been documented on artifacts from the Azores, Bulgaria and China through archaeomagnetic analysis: examining grains in pottery and archaeological ceramic objects in search of clues about Earth’s magnetic activity, scientists reported December 18 in the journal Proceedings of the National Academy of Sciences.
“It’s really exciting that ancient Mesopotamian artifacts 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 science. archaeological data at University College London. Institute of Archeology.
“It shows why preserving the ancient heritage of Mesopotamia is important for science and humanity in general,” Altaweel told CNN in an email.
‘Man-made rocks’
When an ancient artifact contains organic matter, such as bone or wood, scientists can tell its age through radiocarbon dating, which compares the decay ratios preserved in carbon isotopes. But for inorganic artifacts (pottery or ceramic objects), archaeomagnetic analysis is necessary to reveal their age, said the study’s lead 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 vital complement to radiocarbon dating, Howland told CNN.
“Archaeomagnetic dating can be applied to any type of magnetically sensitive materials that have been heated,” Howland said. And its usefulness extends beyond archaeology.
“Geologists often use rock analysis to study the Earth’s magnetic fields, but in more recent times, when there is no possibility of studying very recent rocks because they have not had time to form yet, we need to use archaeological artifacts,” he said. . . “We can think of clay or ceramic bricks as artificial rocks to study the Earth’s magnetic fields.”
Before this new study, there was little precise archaeomagnetic evidence of Mesopotamian artifacts dating from this time.
“The lack of data there really restricted our ability to understand the conditions of the Earth’s magnetic field in that region,” Howland said. He also meant that archaeologists could not accurately calculate the ages 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 agitation of molten metals in the Earth’s core. It prevents our atmosphere from being stripped away by solar winds that blow it away from the sun. While the magnetosphere has had a constant presence for billions of years, its strength waxes and wanes over time. (Human health is not directly affected by magnetic field fluctuations, according to the U.S. Geological Survey.)
Clay artifacts that were fired at high temperatures retain a “imprint” of the Earth’s magnetism at that time in minerals such as iron oxide affected by magnetism. Recovering that 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 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 the Earth’s magnetic field is doing over time and will also help determine the age of artifacts that would otherwise be impossible,” said Cauê S. Borlina. , postdoctoral fellow in the department of Earth and Planetary Sciences at Johns Hopkins University. Borlina, who was not involved in the study, conducts research on ancient and modern magnetic fields and their impact on the formation and habitability of planets.
“Most importantly, these high-resolution records are crucial to understanding how magnetic peaks at the surface might connect to what’s happening inside the 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 a major data gap, but also revealed new clues about the magnetic anomaly from that period.
Of the 32 stones the researchers sampled, five had seals 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 quickly and intensely when they were made. the bricks. Therefore, the seals on the bricks created a snapshot of a surge of magnetic energy that lasted only a few decades.
“The next steps are to continue this work, apply it to more Mesopotamian mud bricks and further improve the curve we can produce of the intensity 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 will be able to look at our data and apply the same techniques to undated artifacts,” he added. “This may 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 magazines.
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