An absolute chronology of Iron Age Jerusalem

Weizmann researchers Prof. Elisabetta Boaretto and Dr. Johanna Regev, in collaboration with a team of archaeologists from the City of David archaeological site in Jerusalem, Dr. Joe Uziel from the Israel Antiquities Authority, and Prof. Yuval Gadot from Tel Aviv University have constructed a detailed chronology of Iron Age Jerusalem—when the city would have served as the capital of the biblical Kingdom of Judah.

Jerusalem has been inhabited continuously for thousands of years, serving as a center of religious significance and a seat of power for kingdoms. Yet, despite the vast number of historical texts about the city, there are still gaps in its absolute chronology. Establishing an absolute chronology involves ascribing the exact dates or periods to archaeological evidence instead of a relative chronology, demonstrating the order of events based on similarities to architecture or ceramic evidence at other sites.

Radiocarbon dating is considered the gold standard for determining the age of ancient artifacts. However, one of the challenges this method faces is the Hallstatt plateau effect, which occurs when cosmic rays interact with Earth’s atmosphere in a way that affects the levels of carbon isotopes in the atmosphere during specific periods. This disruption undermines radiocarbon dating, making dating objects from the 8th to the 5th centuries BCE problematic.

As a result, archaeologists exploring Iron Age Jerusalem have relied more on biblical and historical texts and pottery evidence to establish a timeline rather than using radiocarbon dating. The archaeological challenge is further complicated by the fact that Jerusalem has been continuously inhabited for over 4,000 years, leading to an amalgamation of construction from different periods.

Prof. Boaretto and her colleagues use microarchaeology to tackle the Hallstatt plateau, and their innovative approach involves carefully examining evidence using scientific instruments with an almost forensic-like level of care and attention.

The team first dated organic material found at the site, mostly charred seeds, and then comprehensively analyzed where the seeds were burnt. This process involved Weizmann’s Dangoor Research Accelerator Mass Spectrometry (D-REAMS) Laboratory.

The researchers then utilized 100 calendar-dated tree rings sourced from well-known archives. By integrating the radiocarbon and tree-ring data, the team was able to construct a more precise and detailed determination of the radiocarbon concentration in the atmosphere during the period of interest.

The existence of two historical events with well-established dates—the 586 BCE destruction of Jerusalem by the Babylonians and the 750 BCE earthquake and subsequent reconstruction efforts—helped provide further insights into the radiocarbon behavior in the atmosphere. The researchers noticed differences between the radiocarbon in the material in the region compared to the measured concentration in European and American tree rings from the same time. Understanding these variations, known as “offsets,” is crucial for scientists studying climate and atmosphere conditions and archaeological chronologies.

The study’s biggest accomplishment was the creation of an absolute chronology for a continuously inhabited city, offering unprecedented detail and accuracy. Notably, the researchers provided compelling evidence of widespread human habitation in Jerusalem as early as the 12th century BCE.

The findings were published in Proceedings of the National Academy of Sciences, USA (PNAS). Furthermore, the team’s microarchaeology approach could have broader implications, as problems with Iron Age radiocarbon dating are widespread in archaeological research worldwide.

Boaretto team members (from left): Eugenia Mintz, Dr. Johanna Regev, Prof. Elisabetta Boaretto, and Dr. Lior Regev.

Prof. Elisabetta Boaretto is Head of the Helen and Martin Kimmel Center for Archaeological Science and the incumbent of the Dangoor Chair of Archaeological Sciences. Her research is supported by the Dangoor Research Accelerator Mass Spectrometry Laboratory.