Researchers succeed for the first time in accurately dating a 7,000-year-old prehistoric settlement using cosmic radiation

Researchers at the University of Bern have succeeded for the first time in locating a prehistoric settlement of early farmers in northern Greece that is more than 7,000 years old.

To do this, they combined annual tree ring measurements on wooden building elements with the sudden increase in cosmogenic radiocarbon in 5259 BC. This provides a reliable chronological reference point for many other archaeological sites in southeastern Europe.

Dating finds play a key role in archaeology. It is always important to find out how old a grave, settlement or individual object is. Determining the age of finds from prehistoric times has only been possible for a few decades.

Two methods are used: dendrochronology, which enables dating based on sequences of annual rings in trees, and radiocarbon dating, which can calculate the approximate age of the finds based on the decay rate of the radioactive carbon isotope ¹⁴C is contained in the tree rings.

A team led by the Institute of Archaeological Sciences at the University of Bern has now succeeded in precisely dating wood from the archaeological site of Dispilio in northern Greece, where dating to the year was previously not possible, to various building activities between 5328 and 5140 AD. The researchers used high-energy particles from space that can be reliably dated to 5259 BC. Their research was published in the journal Nature communication.

Tree ring chronologies and the ¹⁴C methods have their limits

Dendrochronology uses characteristic patterns of wide and narrow growth rings in wood that are influenced by climatic conditions. This allows a wooden object to be dated by comparing the annual ring widths with existing standard or regional chronologies.

“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. However, this chronology only applies to certain regions. There is no uniform chronology for the Mediterranean region,” says the study’s lead author, Andrej Maczkowski from the Institute of Archaeological Sciences at the University of Bern.

Therefore, dendrochronological dating from this region using radiocarbon dating must be classified as “pending”. As long as a tree is alive, it absorbs the radioactive isotope ¹⁴C (radiocarbon) contained in the Earth’s atmosphere through photosynthesis. When it dies, it can no longer be absorbed ¹⁴C; The isotope decays with a half-life of 5730 years.

A laboratory measurement method can then be used to determine how much ¹⁴C is still contained within a given tree ring, thus calculating the tree’s approximate time of death over the known half-life.

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

“Until recently, it was therefore believed that dendrochronological dating to the year was possible only if continuous regional tree-ring chronology was available, which is the case for prehistoric periods in only three regions worldwide: this is the southwestern USA, the north foothills of the Alps and England/Ireland,” explains Albert Hafner, Professor of Prehistoric Archeology at the University of Bern and lead author of the study.

Paradigm shift thanks to Japanese physicist

In 2012, a solution to the problem was found: Japanese physicist Fusa Miyake discovered that a massive influx of cosmic rays, presumably due to solar flares, could cause the atmosphere to rise ¹⁴C content that is deposited in the annual rings of the respective years. These peaks can be accurately dated based on long tree-ring chronologies, and because they are global events, they are important anchor points, particularly in regions without consistent tree-ring chronologies.

“Miyake recognized the first anchor points of this kind and thus initiated a paradigm shift in prehistoric archeology,” says Hafner. Today, a dozen of these Miyake events date back to 12,350 BC. BC, and the two important events in 5259 and 7176 BC. BC were only discovered in 2022 by researchers at ETH Zurich.

No such events of comparable magnitude have been recorded in recent centuries. When an event of this magnitude like that of 5259 B.C.E. If it occurs today, it will likely have a catastrophic impact on telecommunications and electronics.

Miyake event enables dating in Dispilio

The research team of the EXPLO project, led by the University of Bern, managed to create a tree ring chronology over a period of 303 years, starting in 5140 BC, by analyzing 787 pieces of wood from the archaeological site of Dispilio on Lake Orestida in northern Greece. ends. The identified settlement phases show various house building activities over 188 years between 5328 and 5140 BC. This exact dating is possible because in this period in 5259 BC. A Miyake event is known.

Researchers at ETH Zurich were able to detect an increase in radiocarbon content during this time by radiocarbon dating several individually defined annual rings. The aim was to transfer this peak, which is reflected worldwide in the annual ring chronologies of the Siberian larch, the American pine and the European oak, to the annual ring chronology of Dispilio in Greece and anchor it with the anchor point 5259 BC. to connect.

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

Maczkowski adds: “We assume that further chronologies for the region from this period can now be linked to the ‘Dispilio chronology’ in rapid succession. This paves the way for the development of a regional dendrochronology for the southern Balkans.”

The oldest lakeside settlements in Europe are located in the Balkans, with sites dating back to shortly after 6000 BC. Be dated. The region played a key role in the expansion of agriculture in Europe.