A cosmic ray sheds new light on the 7,000-year-old settlement of ancient Greece

The researchers used dendrochronology and a radiocarbon jump from 5259 BC to the present, when prehistoric Greek settlements existed more than 7,000 years ago. This new method enables precise dating of other archaeological sites in Southeastern Europe.

Scientists from the University of Bern have for the first time accurately dated the prehistoric settlement of the first farmers in northern Greece to more than 7,000 years ago. They achieved this by combining annual ring measurements on wooden building elements with a significant increase in cosmogenic radiocarbon dating to 5259 BC. This method 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 tomb, settlement or individual object is. Determining the age of finds from prehistoric times has only been possible for several dozen years. Two methods are used for this purpose: dendrochronology, which allows dating based on the sequence of annual tree rings, and radiocarbon dating, which allows calculating the approximate age of finds based on the rate of decay of a radioactive carbon isotope. ¹⁴C contained in tree rings.

A team led by the Institute of Archaeological Sciences at ul University of Bern has now been able to precisely date wood from the archaeological site of Dispilio in northern Greece, where it was previously impossible to date the year, to various types of construction activity between 5328 and 5140 BC. Scientists used high-energy particles from space that can be reliably dated to 5259 BC. Their results research was published May 20 in the journal Nature communication.

Ring chronology i ¹⁴Method C has its limitations

Dendrochronology uses the characteristic patterns of wide and narrow annual wood grains, which are influenced by climatic conditions. Thanks to this, a wooden object can be dated by comparing the width of the annual rings with already existing standard or regional chronologies.

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

Therefore, dendrochronological dating of this region should be classified as “floating” using radiocarbon dating. As long as the tree is alive, it absorbs the radioactive isotope ¹⁴C (radiocarbon) contained in the Earth’s atmosphere through photosynthesis. Once it dies, it will no longer be absorbed ¹⁴C; the isotope decays with a half-life of 5,730 years. You can then use a laboratory measurement method to determine how much ¹⁴C is still contained in the specific ring of the tree, so the approximate time of death of the tree within the known half-life is calculated. “However accuracy such classifications are, at best, within the range of decades,” says Maczkowski.

“Until recently, it was believed that dendrochronological dating to a year was only possible when a continuous regional tree-ring chronology was available, which is the case for prehistoric periods in only three regions of the world: these are the southwestern United States, the northern Alpine foothills, and England/ Ireland,” explains Albert Hafner, professor of prehistoric archeology at the University of Bern and lead author of the study.

A paradigm shift thanks to a Japanese physicist

In 2012, a solution to this problem appeared: Japanese physicist Fusa Miyake discovered that a massive influx of cosmic rays, probably as a result of solar flares, could increase the density of the atmosphere ¹⁴C content that is deposited in the rings of trees of particular years. These spikes can be precisely dated from long tree-ring chronologies, and because they are global in nature, they represent important checkpoints, especially in regions where there are no consistent annual tree-ring chronologies.

“Miyake recognized the first checkpoints of their kind and thus caused a paradigm shift in prehistoric archaeology,” says Albert Hafner. Today there are a dozen of them Miyake Events are known until 12,350 BC, and two important events from 5259 and 7176 BC were only discovered in 2022 by researchers from ETH Zurich. No events of a similar scale have been recorded in the last few centuries. If an event of the scale of 5259 BC were to occur today, it would likely have a catastrophic impact on telecommunications and electronics.

The Miyake event allows dating on Dispilio

An EXPLO research team led by the University of Bern managed to establish an annual ring chronology spanning 303 years and ending in 5140 BC by analyzing 787 pieces of wood from the Dispilio archaeological site on Lake Orestida in northern Greece. The identified settlement phases show various house-building activities over a 188-year period, between 5328 and 5140 BC. This precise dating is possible because the famous Miyake event occurred during this period in 5259 BC.

Scientists at ETH Zurich were able to detect a sharp increase in radiocarbon content during this time by radiocarbon dating several individually defined annual rings. The idea was therefore to recreate this peak, which is reflected globally in the annual ring chronology of Siberian larch, American pine and European oak, on the annual ring chronology from Dispilio in Greece and link it to the checkpoint of 5259 BC. “The Balkans are 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 Albert Hafner.

Andrej Maczkowski adds: “We expect that other chronologies for the region from this period will now be able to be linked to the “Chronologia Dispilio” in quick succession. It paves the way for the development of regional dendrochronology for the southern Balkans. “The Balkans are home to the oldest lakeside settlements in Europe, dating back to just after 6000 BC. The region played a key role in the development of agriculture in Europe.

Reference: “Absolute Dating of the European Neolithic Using a 14C Fast Trip in 5259 BC” by Andrej Maczkowski, Charlotte Pearson, John French, Tryfon Giagkoulis, Sönke Szidat, Lukas Wacker, Matthias Bolliger, Kostas Kotsakis and Albert Hafner, May 20, 2024 , Nature communication.
DOI: 10.1038/s41467-024-48402-1