Mesopotamian bricks unveil the strength of Earth's ancient magnetic field

Ancient bricks inscribed with the names of Mesopotamian kings have yielded important insights into a mysterious anomaly in Earth's magnetic field 3,000 years ago, according to a new study involving UCL researchers.

The research, published in the Proceedings of the National Academy of Sciences (PNAS), describes how changes in the Earth's magnetic field imprinted on iron oxide grains within ancient clay bricks, and how scientists were able to reconstruct these changes from the names of the kings inscribed on the bricks.

The team hopes that using this "archaeomagnetism," which looks for signatures of the Earth's magnetic field in archaeological items, will improve the history of Earth's magnetic field, and can help better date artefacts that they previously couldn't.

Co-author Professor Mark Altaweel (UCL Institute of Archaeology) said: "We often depend on dating methods such as radiocarbon dates to get a sense of chronology in ancient Mesopotamia. However, some of the most common cultural remains, such as bricks and ceramics, cannot typically be easily dated because they don't contain organic material. This work now helps create an important dating baseline that allows others to benefit from absolute dating using archaeomagnetism."

The Earth's magnetic field weakens and strengthens over time, changes which imprint a distinct signature on hot minerals that are sensitive to the magnetic field.

The team analysed the latent magnetic signature in grains of iron oxide minerals embedded in 32 clay bricks originating from archaeological sites throughout Mesopotamia, which now overlaps with modern day Iraq.

The strength of the planet's magnetic field was imprinted upon the minerals when they were first fired by the brickmakers thousands of years ago.

At the time they were made, each brick was inscribed with the name of the reigning king which archaeologists have dated to a range of likely timespans.

Together, the imprinted name and the measured magnetic strength of the iron oxide grains offered a historical map of the changes to the strength of the Earth's magnetic field.

The researchers were able to confirm the existence of the "Levantine Iron Age geomagnetic Anomaly," a period when Earth's magnetic field was unusually strong around modern Iraq between about 1050 to 550 BCE for unclear reasons.

Evidence of the anomaly has been detected as far away as China, Bulgaria and the Azores, but data from within the southern part of the Middle East itself had been sparse.

Lead author Professor Matthew Howland of Wichita State University said: "By comparing ancient artefacts to what we know about ancient conditions of the magnetic field, we can estimate the dates of any artifacts that were heated up in ancient times."

To measure the iron oxide grains, the team carefully chipped tiny fragments from broken faces of the bricks and used a magnetometer to precisely measure the fragments.

By mapping out the changes in Earth's magnetic field over time, this data also offers archaeologists a new tool to help date some ancient artefacts.

The magnetic strength of iron oxide grains embedded within fired items can be measured and then matched up to the known strengths of Earth's historic magnetic field.

The reigns of kings lasted from years to decades, which offers better resolution than radiocarbon dating which only pinpoints an artefact's date to within a few hundred years.

An additional benefit of the archaeomagnetic dating of the artefacts is it can help historians more precisely pinpoint the reigns of some of the ancient kings that have been somewhat ambiguous.

Though the length and order of their reigns is well known, there has been disagreement within the archaeological community about the precise years they took the throne resulting from incomplete historical records.

The researchers found that their technique lined up with an understanding of the kings' reigns known to archaeologists as the "Low Chronology."

The team also found that in five of their samples, taken during the reign of Nebuchadnezzar II from 604 to 562 BCE, the Earth's magnetic field seemed to change dramatically over a relatively short period of time, adding evidence to the hypothesis that rapid spikes in intensity are possible.

Read more at Science Daily

Ancient Mesopotamian discovery transforms knowledge of early farming

Rutgers researchers have unearthed the earliest definitive evidence of broomcorn millet (Panicum miliaceum) in ancient Iraq, challenging our understanding of humanity's earliest agricultural practices. Their findings appear in the journal Scientific Reports.

"Overall, the presence of millet in ancient Iraq during this earlier time period challenges the accepted narrative of agricultural development in the region as well as our models for how ancient societies provisioned themselves," said Elise Laugier, an environmental archaeologist and National Science Foundation postdoctoral fellow in the School of Arts and Sciences at Rutgers University-New Brunswick.

Broomcorn millet is an "amazingly robust, quick-growing and versatile summer crop" that was first domesticated in East Asia, Laugier added. The researchers analyzed microscopic plant remains (phytoliths) from Khani Masi, a mid-late second millennium BCE (c. 1500-1100 BCE) site in the Kurdistan region of Iraq.

"The presence of this East Asian crop in ancient Iraq highlights the interconnected nature of Eurasia during this time, contributing to our knowledge of early food globalization," Laugier said. "Our discovery of millet and thus the evidence of summer cultivation practices also forces us to reconsider the capacity and resilience of the agricultural systems that sustained and provisioned Mesopotamia's early cities, states and empires."

The discovery of broomcorn millet in ancient Mesopotamia was surprising for environmental and historical reasons. Until now, researchers thought that millet wasn't grown in Iraq until the construction of later 1st millennium BCE imperial irrigation systems. Millet generally requires summer precipitation to grow, but Southwest Asia has a wet-winter and dry-summer climate, and agricultural production is based almost entirely on crops grown during the winter, such as wheat and barley.

Agricultural production is thought to be the basis for supporting and provisioning Mesopotamian cities, states and empires. The researchers' new evidence that crops and food were, in fact, grown in summer months means that previous studies likely vastly under-appreciated the capacities and resilience of ancient agricultural food-system societies in semi-arid ecosystems.

The new study is also part of growing archaeological research showing that in the past, agricultural innovation was a local initiative, adopted as part of local diversification strategies long before they were used in imperial agricultural intensification regimes -- new information that could have an impact on how agricultural innovations move forward today.

"Although millet isn't a common or preferred food in semi-arid Southwest Asia or the United States today, it is still common in other parts of Asia and Africa," Laugier said. "Millet is a hearty, fast-growing, low-water requiring and nutritious gluten-free grain that could hold a lot of potential for increasing the resilience capacities of our semi-arid food systems. Today's agricultural innovators should consider investing in more diverse and resilient food systems, just as people did in ancient Mesopotamia."

Read more at Science Daily