In the vicinity of the Tigris River, adjacent to the historical city of Kalhu (now Nimrud) in northern Iraq, a brickmaker played an unwitting role in preserving a remarkable slice of history. Crafted for the construction of a palace dedicated to King Ashurnasirpal II over 2,900 years ago, a clay brick has transcended time, serving as a repository of ancient DNA that sheds light on the flora of that era. A recent collaborative study conducted by researchers from the University of Copenhagen, the University of Oxford, and Aalborg University delves into the meticulous extraction and analysis of this genetic material, revealing valuable insights into the plant life of the past.
The journey began during a digitalization initiative at the National Museum of Denmark in 2020, where Dr. Sophie Lund Rasmussen and her team procured samples from the brick's inner core. Due to the brick's mode of formation, DNA contamination risk was minimal. Drawing from techniques applied to porous materials like bone, the researchers successfully extracted DNA from the samples.
Sequencing the extracted DNA enabled the identification of 34 distinct taxonomic plant groups. Notable among these were the Brassicaceae (cabbage) and Ericaceae (heather) families, while others included Betulaceae (birch), Lauraceae (laurels), Selineae (umbellifiers), and Triticeae (cultivated grasses). Through a multidisciplinary approach involving specialists in Assyriology, archaeology, biology, and genetics, these findings were compared with both modern-day botanical records from Iraq and ancient Assyrian plant descriptions.
The clay brick, likely composed of mud collected near the Tigris river, underwent shaping within a mold, followed by inscription with cuneiform script before drying in the Sun. Its unique preservation stemmed from the natural drying process, as opposed to firing. This method trapped genetic material within the clay, safeguarding it over the centuries.
Dr. Sophie Lund Rasmussen expressed enthusiasm about the successful extraction of ancient DNA from the clay brick, underscoring the value of this interdisciplinary study. The diverse expertise involved in the project facilitated a comprehensive investigation and yielded remarkable results. The study exemplifies the power of interdisciplinary collaboration in scientific exploration.
The brick's inscriptions enable the precise dating and regional allocation of the clay. This grants the brick the status of a biodiversity time capsule, offering a wealth of information about a specific site and its surroundings. Dr. Troels Arbøll from the University of Oxford emphasized that the brick provides unparalleled access to the world of ancient Assyrians, enhancing our understanding of their environment.
The study's findings, published in Scientific Reports, underscore the potency of genetics in unraveling historical mysteries. By tapping into an unassuming clay brick, researchers have illuminated the botanical diversity of an ancient era, fostering appreciation for the rich tapestry of life that once thrived along the banks of the Tigris River.