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.

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Researchers extract ancient DNA from a 2,900-year-old clay brick, revealing a time capsule of plant life

Currently housed at the National Museum of Denmark, the clay brick originates from the palace of Neo-Assyrian king Ashurnasirpal II, in the ancient city of Kalhu. Known today as the North-West palace in Nimrud (modern-day northern Iraq), its construction began around 879 BCE. The brick has a cuneiform inscription (written in the now extinct Semitic language Akkadian) stating that it is 'The property of the palace of Ashurnasirpal, king of Assyria.' This makes it possible to date the brick precisely to within a decade (879 BCE to 869 BCE).

During a digitalization project at the Museum in 2020, the group of researchers were able to obtain samples from the inner core of the brick -- meaning that there was a low risk of DNA contamination since the brick was created. The team extracted DNA from the samples by adapting a protocol previously used for other porous materials, such as bone.

After the extracted DNA had been sequenced, the researchers identified 34 distinct taxonomic groups of plants. The plant families with the most abundant sequences were Brassicaceae (cabbage) and Ericaceae (heather). Other represented families were Betulaceae (birch), Lauraceae (laurels), Selineae (umbellifiers) and Triticeae (cultivated grasses).

With the interdisciplinary team comprising assyriologists, archaeologists, biologists, and geneticists, they were able to compare their findings with modern-day botanical records from Iraq as well as ancient Assyrian plant descriptions.

The brick would have been made primarily of mud collected near the local Tigris river, mixed with material such as chaff or straw, or animal dung. It would have been shaped in a mould before being inscribed with cuneiform script, then left in the sun to dry. The fact that the brick was never burned, but left to dry naturally, would have helped to preserve the genetic material trapped within the clay.

Dr Sophie Lund Rasmussen (Wildlife Conservation Research Unit, Department of Biology, University of Oxford), joint first author of the paper, said: 'We were absolutely thrilled to discover that ancient DNA, effectively protected from contamination inside a mass of clay, can successfully be extracted from a 2,900-year-old clay brick. This research project is a perfect example of the importance of interdisciplinary collaboration in science, as the diverse expertise included in this study provided a holistic approach to the investigation of this material and the results it yielded.'

In addition to the fascinating insight this individual brick revealed, the research serves as a proof of concept and method which could be applied to many other archaeological sources of clay from different places and time periods around the world, to identify past flora and fauna. Clay materials are nearly always present in any archaeological site around the world, and their context means they can often be dated with high precision.

This study only described the plant DNA extracted, as these were the most prevalent and best-preserved specimens. However, depending on the sample, all taxa could potentially be identified, including vertebrates and invertebrates. The ability to provide accurate descriptions of ancient biodiversity would be a valuable tool to better understand and quantify present day biodiversity loss, and to gain a deeper understanding of ancient and lost civilisations.

Read more at Science Daily

Building bricks from waste materials

Firing bricks and making mortar and cement is very costly, but organic chemists at Flinders University are working on more sustainable alternatives -- focusing on building materials made from waste products.

In another move into the circular economy, researchers from the Flinders Chalker Lab have used low-cost feedstocks to make lightweight but durable polymer building blocks which can be bonded together with an adhesive-free chemical reaction.

Their latest study tested the strength of these materials and explored ways they can be reinforced in construction.

Matthew Flinders Professor of Chemistry, Justin Chalker, says the need to develop sustainable building materials is increasingly important, with cement, iron and steel production accounting for more than 15% of global CO2 emissions each year.

"In this study, we tested a new type of brick we can make from waste cooking oil, mixed with sulfur and dicyclopentadiene (DCPD). Both sulfur and DCPD are byproducts of petroleum refining.

"The bricks bond together without mortar upon application of a trace amount of amine catalyst.

"All the starting materials are plentiful and can be classified as industrial waste.

"This research is part of a larger effort to move towards a sustainable built environment," says project leader Professor Chalker.

The Chalker Lab's new polymer research team at Flinders University's College of Science and Engineering is collaborating with Clean Earth Technologies for further development. scale-up and possible commercialisation.

The latest study, published as a cover feature in a special issue on Sustainability in the journal Macromolecular Chemistry and Physics, expanded the research to test the new bricks' mechanical properties and look at ways to reinforce them in construction, including with carbon fibre fillers.

Chalker Lab research associate Dr Maximilian Mann says as well as repurposing waste materials into value-added construction materials, the polymer bricks' sulfur-sulfur bond means they can be bound together without mortar like traditional building method.

"The bonding in this novel catalytic process is very strong, producing a sustainable construction material with its own mortar which will potentially streamline construction," Dr Mann says.

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