Time capsule of plant life extracted from 2,900-year-old clay brick

In a new study published in the journal Nature Scientific Reports, researchers have successfully extracted ancient DNA from a 2,900-year-old clay brick, uncovering a wealth of information about the plant life cultivated during that era. 

While offering an invaluable look into the past, this monumental research also opens the door for similar studies on clay material from various sites and time periods.

King of Assyria

The clay brick analyzed for the study is currently housed at the National Museum of Denmark. It originates from the palace of Neo-Assyrian king Ashurnasirpal II, in the ancient city of Kalhu, now known as the North-West palace in Nimrud, modern-day northern Iraq. 

The construction of this palace commenced around 879 BCE. Remarkably, the brick carries a cuneiform inscription in the extinct Semitic language Akkadian, declaring it as “The property of the palace of Ashurnasirpal, king of Assyria.”

This inscription enables researchers to date the brick with remarkable precision, to within a decade (879 BCE to 869 BCE).

DNA sequencing 

The extraction of DNA from the brick’s inner core was conducted during a digitalization project at the Museum in 2020, minimizing the risk of DNA contamination since the creation of the brick. 

The research team adapted a protocol previously used for other porous materials, such as bone, to extract the DNA. The sequencing of the extracted DNA led to the identification of 34 distinct taxonomic groups of plants. 

Botanical records 

Notably, the most abundant sequences belonged to the Brassicaceae (cabbage) and Ericaceae (heather) families. Other identified families included Betulaceae (birch), Lauraceae (laurels), Selineae (umbellifers), and Triticeae (cultivated grasses).

The interdisciplinary research team, which included assyriologists, archaeologists, biologists, and geneticists, compared their findings with modern-day botanical records from Iraq and ancient Assyrian plant descriptions.

Protected mass of clay 

The brick was primarily made of mud collected from the nearby Tigris river, mixed with materials like chaff, straw, or animal dung, then shaped in a mold, inscribed with cuneiform script, and left to dry naturally in the sun. 

The absence of burning in the brick-making process contributed to the preservation of genetic material within the clay.

Dr. Sophie Lund Rasmussen is the joint first author of the paper and a member of the Wildlife Conservation Research Unit at the University of Oxford.

‘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,” said Dr. Rasmussen.

“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.’

Study implications 

Beyond the insight provided by this individual brick, the research serves as a proof of concept and method that could be applied to various archaeological sources of clay from different places and time periods worldwide to identify plants and animals of the past. 

Clay materials can be found in archaeological sites worldwide, and their context often allows for highly precise dating.

While this study focused on plant DNA, as these specimens were the most prevalent and well-preserved, the method has the potential to identify all taxa, including vertebrates and invertebrates. 

The ability to accurately describe ancient biodiversity is a valuable tool for understanding and quantifying present-day biodiversity loss and gaining deeper insights into ancient and lost civilizations.

Dr. Troels Arbøll is the joint first author of the paper and was a junior research fellow at Faculty of Asian and Middle Eastern Studies at the University of Oxford when the study was conducted.

“Because of the inscription on the brick, we can allocate the clay to a relatively specific period of time in a particular region, which means the brick serves as a biodiversity time-capsule of information regarding a single site and its surroundings,” said Dr. Arbøll. “In this case, it provides researchers with a unique access to the ancient Assyrians.”

Image Credit: Arnold Mikkelsen og Jens Lauridsen

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