New research on ancient Mesopotamia has uncovered evidence of an ancient magnetic phenomena, providing a way to delve deeper into one of the most fascinating periods in human history.
Scientists have analyzed ancient bricks from Mesopotamia and revealed just how dramatic an ancient spike in Earth’s magnetic field, some 3,000 years ago, truly was. The study, published Monday in Proceedings of the National Academy of Sciences, relies on archaeomagnetic techniques, or extracting information about the strength and direction of the Earth’s magnetic field from ancient objects.
“It is a study that investigates magnetic memories of materials”, explained Philip McCausland of Western University in Canada, director of Western Paleomagnetic and Petrophysical Laboratory. Items like bricks or pottery were often made with grains of magnetic rock that, when heated and then cooled, keep a signature of the geomagnetic conditions of the time.
“At high temperatures the items are memoryless. McCausland explained to Motherboard that as temperature falls, the object begins to remember the Earth’s magnet field it was in.
In the study, researchers investigated field strength using ancient Mesopotamian bricks containing iron oxide. The researchers were able to get the ratio of magnetic charges in both the laboratory and the past by heating the bricks, cooling them, and then replacing the magnetic fields with those produced in the laboratory.
This told researchers that these bricks were fired at a time when the Earth’s magnetic field was more than one and a half times what it is today, during a period known as the Levantine Iron Age geomagnetic anomaly. The same team discovered the anomaly using the same methods in another region, on rock layers.
” This period saw extremely high intensities of earth’s magnet field. Higher than anyone thought possible in such a brief time span,” explained Matthew Howland. He is an anthropological-archaeologist from Wichita State University. Researchers’ findings confirmed the strength of the magnetic field in the area at that time. Previous studies had not been able to confirm this.
There’s been a lot of recent interest in studying this region and time period. “During…the first three millennia BCE, you see the development of cities for the first time, the development of these incredibly complex societies like the Babylonians, and the development of agriculture for the first time in this region,” said Howland.
Howland and collaborators explain that antiquated methods have held this research back. Previously, archaeologists relied almost solely on inscriptions or knowing when different types of inscribed bricks were used to date ancient objects.
“Historical inscriptions have always been instrumental in archaeological research to synchronize important events,” said study co-author, historian Shai Gordin in a press statement. “But there are very few scientific methods that can help us corroborate the specific date of an inscription, let alone one that can be independently judged against the possible dates of other dated inscriptions.”
“Our research really provides a basis for future archaeologists to apply archaeomagnetic techniques to date material that wouldn’t previously be datable at these archeological sites, like ceramics,” said Howland. Radiocarbon dating, he explained, doesn’t work for many of these ancient treasures because they don’t contain the C-14 carbon isotope that the process requires.
This technique isn’t just valuable to archaeologists: It also might be a boon for geologists desperate to understand Earth’s changing magnetic field. Scientists can use these techniques to look back at the time before direct magnetic measurements were made. Scientists only started taking these measurements from specific locations around the world 400 years ago, explained McCausland, and only started taking global measurements with the advent of satellites. He said, “We’d like to see what field looked like in much older times.”
The supercharged anomaly from the Levantine Iron Age is particularly perplexing. The researchers don’t know much about the cause of the intensity spike or how and why the Earth produces these peaks over time.
“The Geomagnetic Field is one of Earth Sciences’ most mysterious phenomena,” Lisa Tauxe said in a statement to the press. “Albert Einstein said that the origin and behavior of this field was one of the greatest unsolved physics problems.”
The study, according to McCausland is “impressive,” both due to the diversity of scientists involved and because it is difficult to establish the strength of the magnetic field. “Most often specimens fail, they actually aren’t good fidelity recorders because, usually, when you bake something again it undergoes some chemical transformations and you lose some of the ability to retain a memory and we don’t end up with a good record. That’s the fate of a good many if not most samples,” he said. “It’s so painstaking to get a clear answer and they’ve done a good job here.”
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