Neolithic settlement dated accurately to the year thanks to cosmic rays

A 7,000-year-old Neolithic settlement in modern-day Greece has for the first time been accurately dated down to the precise years it was built.

The findings could provide a reference point in time to help date other archaeological sites in southeastern Europe.

Archaeologists from the University of Bern in Switzerland were able to date the site, called Dispilio, using a combination of annual growth ring measurements on wooden building components and an additional out-of-this-world method: cosmic rays. Their research is published in the journal Nature Communications.

Dating prehistoric wooden elements uses two methods.

One is dendrochronology, in which tree rings are analysed. A wooden object’s growth rings are impacted by certain climatic and regional conditions which can be compared to other known examples.

“In central Europe, there is a tree-ring chronology that goes back almost 12,500 years into the past – to the year 10,375 BC,” says lead author, Andrej Maczkowski from the Institute of Archaeological Sciences at the University of Bern. “However, this chronology only applies to certain regions. There is no consistent chronology for the Mediterranean region.”

The other method is radiocarbon dating, in which the presence of radioactive carbon isotope 14C, or carbon-14, is measured.

Carbon-14 is absorbed by living organisms through their lifetime. When they die, carbon-14 radioactively decays into other atoms.

“However, the accuracy of such classifications is, in the best case, within the range of decades,” Maczkowski adds.

“Until recently, it was therefore believed that dendrochronological dating to the year was only possible if a continuous regional tree-ring chronology was available, which is the case for prehistoric periods in just 3 regions worldwide: this is the southwestern United States, the northern Alpine foothills and England/Ireland,” explains senior author Albert Hafner.

But in 2012, Japanese physicist Fusa Miyake suggested that a massive influx of cosmic rays, such as those produced by solar flares, would increase the amount of 14C in the atmosphere. Such events today might have major impacts on telecommunications and electronics.

These global events in history could be used as “markers” in tree rings. Dozens have been identified, including 2 discovered in 2022: one in 7176 BCE and another in 5259 BCE.

Using the latter of these markers, the archaeologists analysed 787 pieces of timber from Dispilio on Lake Orestida in what is today northern Greece.

They identified 303 years of growth ring chronology for the region and could show settlement and housebuilding at the site over 188 years between 5328 and 5140 BCE.

“The Balkans is therefore the first region in the world to benefit from this paradigm shift and to be able to successfully determine absolute dating independently of a consistent calendar,” says Hafner.

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