19 h hours ago|Source: Proceedings of the National Academy of Sciences, EurekAlert, ScienceAlert
A clay tablet from the reign of Nebuchadnezzar II.
Archaeologists have used changes in the Earth’s magnetic field to better understand the history of the still poorly described Mesopotamia. And at the same time, they used this technique to describe a strange event that happened in ancient times in the territory of present-day Iraq.
Bricks made from clay in Mesopotamia about three thousand years ago contain grains of iron oxide. Thanks to new technologies, they can reveal a lot of details about a world that no longer exists. For their analysis, the scientists used changes in the magnetic field, which surrounds the Earth with a protective barrier. In a new survey, they tried to find out if this technology can be used in archeology and what it can reveal. It turned out that the use is multiple – both in dating, but also in describing how dramatically the Earth’s magnetic field changed.
“When determining chronology in ancient Mesopotamia, we often depend on methods such as the radiocarbon method,” describes the archaeologist Mark Altaweel from University College London. “Some of the most common cultural remains, such as bricks and pottery, however, are usually not easily dated because they do not contain organic material. This work is now helping us create an important foundation that will enable others to use absolute dating using archaeomagnetism,” he explains.
Wandering magnetic poles
The Earth’s magnetic field is not static, but changes over time. Its origin is a giant natural dynamo in the core of our planet – a rotating, convective and electrically conductive fluid there transforms kinetic energy into electric and magnetic fields, which then propagate into the surrounding space. Changes in the magnetic field can be the result of external influences, such as the solar wind, or changes inside the planet where the dynamo is spinning.
Whatever these changes are caused by, our science can already record them, and even use data from the past. For example, in molten magma, magnetic grains line up with the Earth’s magnetic field and settle in that position as the magma cools and simultaneously solidifies into volcanic rock.
Scientists can use these rocks as a record of the magnetic field, a field known as paleomagnetism. Archaeologists led by Matthew Howland from Wichita State University in the United States thought they could use this method for their field as well.
It may sound complicated, but the technique is actually quite simple. Each of the 32 Mesopotamian clay bricks studied has an embossed seal with the name of the king who ruled at the time it was made. In order to date the material, the researchers narrowed down the most likely range of years during which individual kings reigned.
Then they chipped off a piece of each brick and measured the arrangement of the microscopic grains of iron oxide embedded in them using a magnetometer. This technique allowed them to broadly reconstruct the behavior of the planetary magnetic field over a period of roughly two thousand years, from the third to the first millennium BC. They then compared the results with other reconstructions of the magnetic field available to them from other archaeomagnetic studies. And thus they came to two important results.
A magnetic mystery
Taken together, this large body of data from around the world suggests that something very strange happened to the magnetic field between 1050 and 550 BC. Scientists call this phenomenon the LIAA, or Levantine Iron Age Geomagnetic Anomaly. There was a still inexplicable jump in the intensity of the magnetic field in the territory of today’s Iraq.
Reconstruction of data from Mesopotamian plates confirmed the existence of the LIAA and provided one of the few records of this anomaly from Iraq itself. Additionally, the analysis revealed brief, dramatic fluctuations during the reign of Nebuchadnezzar II. approximately between 604 and 562 BC, showing that the Earth’s magnetic field can change quite significantly over a short time horizon.
The second success of the study is that comparing bricks to a magnetic field works in reverse. From the scattering of magnetic grains, they can determine with high precision the time of the creation of the plaques, and thus also the reign of the ruler who is mentioned on them.
Scientists thus have in their hands a tool for the future very precise confirmation of the dates when which kings ruled Mesopotamia. Which is essential for them: although historians know the order of the rulers well, they lack the exact dates of the accession of new rulers to the throne. Historical records are imprecise, confused, and insufficient, so further application of this method can greatly assist dating in the distant past.
2023-12-23 08:30:58
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