Ancient Inscribed Bricks Contain Evidence of Mysterious Magnetic 'Anomaly,' Scientists Find

New research on ancient Mesopotamia has uncovered evidence of an ancient magnetic phenomenon, 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 basically investigates the magnetic memory of materials,” explained Philip McCausland, the director of the Western Paleomagnetic and Petrophysical Laboratory at Canada’s Western University, who wasn’t involved in the study. 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 very high temperatures, the objects are memoryless. But as the temperature drops it picks up a memory of the Earth’s magnetic field that it was sitting in at the time,” McCausland told Motherboard.

In this study, researchers used ancient bricks from Mesopotamia (which overlaps modern-day Iraq) containing iron oxide to investigate field strength. By systematically removing the ancient magnetic signature from small fragments of the bricks through heating and cooling, then reheating the bricks and replacing the magnetic field with one produced in the lab, they could get a ratio between the object's magnetic charge in the past and under laboratory conditions.

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 anomaly was first discovered in 2009 by members of the same team in a nearby region using similar methods, but on layers of rock material. 

“This period was seeing extremely high intensities in earth’s magnetic field, higher even than people really thought was possible for such a short span of time,” said study co-author Matthew Howland, an anthropological archaeologist at Wichita State University. The researchers’ findings confirm just how strong the magnetic field was in the region at the time, something that wasn’t possible in previous studies.

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. 

But, as Howland and his collaborators explained, this research has been held back by antiquated techniques. 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. These techniques allow scientists to peer back in time to before they began taking direct measurements of the magnetic field. 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. “We would like to know what the field was much further in the past,” he said.

The supercharged anomaly from the Levantine Iron Age is particularly perplexing. Researchers don’t understand much about what caused the spike in intensity or why and how the Earth generates these kinds of peaks periodically throughout time. 

“The geomagnetic field is one of the most enigmatic phenomena in earth sciences,” said Lisa Tauxe, co-author and geophysicist, in a press statement. “Albert Einstein himself said that understanding its origin and behavior was one of the great unsolved problems in physics.” 

The study is “impressive” according to McCausland, both because of the diverse team of social and physical scientists who worked on it, and also because the technique of establishing the field strength is rife with difficulty. “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.”