Researchers from the USA, Israel and the United Kingdom describe in the magazine Proceedings of the National Academy of Sciences (PNAS) how changes in the The Earth’s magnetic field They have left their mark on the ancients Mesopotamian bricksin today’s Iraq.
The team hopes that the use of these “Archaeomagnetism“Improving knowledge and dating of both the Earth’s magnetic field itself and some archaeological objects that have not previously been dated.”
“The fired and inscribed clay bricks from this period, between the 3rd and 1st millennium BC. 2000 BC, provide an excellent basis for understanding the conditions of the magnetic field, as these artifacts are well dated thanks to their inscriptions naming individual kings.” , Points to SINC, the lead author, Professor Matthew D HowlandResearcher at Wichita State University (USA).
These fired clay bricks from Mesopotamia with inscriptions from kings between the 3rd and 1st millennium BC. BC provide an excellent basis for understanding magnetic field conditions.
The professor explains that these clay or mud bricks were made using a technology similar to that of today’s bricks: with Earth and straw compacted in a wooden frame before being dried in the sun or fired in the kiln. “Only the baked bricks “They can be used for archaeomagnetic analyses,” he emphasizes.
Because they were more expensive, they were only used in palaces and temples, especially in areas that required high resistance to foot traffic or water. The kings inscribed their names on them as a sign of their power to build these monumental buildings and as a sign of devotion to their gods.
Grains with iron oxide
The Earth’s magnetic field, in turn, weakens and strengthens over time, changes that give a distinctive signature to the heated minerals that respond to that field. The team analyzed the latent magnetic signature in embedded iron oxide grains 32 clay bricks come from archaeological sites throughout Mesopotamia. To make the measurements, the team carefully carved tiny fragments from the parts’ fracture surfaces and used a magnetometer.
The strength of the planet’s magnetic field was imprinted on these minerals when brickmakers first fired the pieces thousands of years ago. The names of the kings engraved on the iron oxide grains and the measured magnetic intensity made it possible to create a Historical map of changes in magnetic field intensity from Earth.
Mysterious disturbance in the magnetic field
This allowed them to confirm a mysterious disturbance in the Earth’s magnetic field that occurred 3,000 years ago. It is called “Levantine Iron Age geomagnetic anomaly“, a period when, for reasons that are unclear, this field was unusually intense around what is now Iraq between 1050 and 550 BC. Signs of this anomaly have already been discovered in China, Bulgaria and the Azores, but the dates are in the south of the Near East has been tight so far.
In addition, by mapping changes in the Earth’s magnetic field over time, archaeologists have a new tool to better date ancient objects. The reigns of kings lasted from years to decades, and this new technique provides better resolution than radiocarbon dating, which can only date an artifact to a few hundred years.
In the words of the co-author Mark Altaweelfrom University College London: “We often rely on dating methods such as these radiocarbon dates to get an idea of the chronology in ancient Mesopotamia. However, some of the more common cultural remains, such as bricks and pottery, cannot be easily dated because they do not contain organic material. This work now helps to provide an important dating basis that will enable others to benefit from absolute dating using archaeomagnetism.”
This work helps provide an important dating base that will enable others to benefit from absolute dating by archaeomagnetism.
For his part, Howland adds: “This study lays the foundation for future archaeomagnetic dating of unlabeled objects from Mesopotamia, such as: Ceramic pots, which can usually only be dated by their typology, a crude and imprecise dating method. For example, the researchers discovered that their technique was consistent with an interpretation of the reigns of kings that archaeologists call “low chronology.”
The team also found in five of their samples taken during the reign of Nebuchadnezzar IIbetween 604 and 562 BC 4000 BC that the Earth’s magnetic field appeared to change dramatically in a relatively short period of time, providing evidence for the hypothesis that rapid peaks in intensity are possible.
Accordingly Lisa TauxeCo-author from Scripps Oceanographic Institution (USA): “The Earth’s magnetic field is one of the most puzzling phenomena of geosciences. The well-dated archaeological remains of rich Mesopotamian cultures, particularly bricks bearing the names of specific kings, provide an unprecedented opportunity to study the Changes in field intensity with high temporal resolutionto track changes that have occurred over several decades or even less.”
“Our study provides a basis for absolute dating of some of the world’s most important sites.” History of the development of urban planning and social complexity in the Mesopotamian region, an incredibly important region for understanding our past,” Howland concludes.
Reference:
Matthew D Howland et al. “Exploring geomagnetic variations in ancient Mesopotamia: Archaeomagnetic study of inscribed bricks from the 3rd-1st century.” millennium B.C. PNAS, 2023. Research funded by the United States-Israel Binational Science Foundation.