Ancient bricks from Mesopotamia have helped confirm a mysterious anomaly in Earth’s magnetic field that occurred 3,000 years ago, a brand new study finds.
Brickmakers baked the bricks, which were imprinted with the names of Mesopotamian kings, between the third and first millennia B.C. Iron oxide grains inside the clay recorded changes in Earth’s magnetic field when the bricks were heated, enabling scientists to reconstruct changes within the magnetic field over time, the team reported in a study published within the journal PNAS on Monday (Dec. 18).
The finding may help scientists date artifacts in the long run, the team said.
“We frequently rely on dating methods equivalent to radiocarbon dates to get a way of chronology in ancient Mesopotamia,” study co-author Mark Altaweel, a professor of Near East archaeology and archaeological data science at University College London, said in a statement. “Nonetheless, a few of the commonest cultural stays, equivalent to bricks and ceramics, cannot typically be easily dated because they do not contain organic material. This work now helps create a very important dating baseline.”
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To research Earth’s magnetic field — which waxes, wanes and even flips over time — the researchers checked out grains of the mineral iron oxide in 32 clay bricks from ancient Mesopotamia, positioned largely in what’s now Iraq. These minerals are sensitive to the magnetic field, and after they are heated — for instance after they are fired during brickmaking — they maintain a definite signature from Earth’s magnetic field, the researchers said within the statement.
Each brick was inscribed with the name of one in all 12 Mesopotamian kings during each ruler’s reign, which archaeologists already had dates for based on earlier findings. The team measured the magnetic strength of the iron oxide grains in each brick by chipping tiny fragments off the bricks’ broken faces and using a magnetometer to measure the magnetic field strength of the minerals inside. By combining the dates of the kings’ reigns with the measured field strength, the researchers created a timeline showing the ups and downs of Earth’s magnetic field over time in Mesopotamia.
Their research supported evidence for the “Levantine Iron Age geomagnetic Anomaly,” a time when the planet’s magnetic field was surprisingly strong around what’s now Iraq between 1050 and 550 B.C. It’s unclear why this anomaly existed during that period, but evidence for it has been detected as far-off as China, Bulgaria and the Azores within the North Atlantic. Until now, evidence within the Middle East for the anomaly had been sparse, the researchers said.
In five of the samples, dating to the reign of Nebuchadnezzar II (circa 604 to 562 B.C.), the grains indicated that Earth’s magnetic field shifted dramatically over the period.
“The geomagnetic field is one of the enigmatic phenomena in earth sciences,” study co-author Lisa Tauxe, a professor of geophysics on the Scripps Institution of Oceanography in California, said within the statement. “The well-dated archaeological stays of the wealthy Mesopotamian cultures, especially bricks inscribed with names of specific kings, provide an unprecedented opportunity to check changes in the sphere strength in high time resolution, tracking changes that occurred over several many years and even less.”