A cosmic ray sheds new light on a 7,000-year-old ancient Greek settlement

The researchers used dendrochronology and radiocarbon dating from 5259 BC to date a prehistoric Greek settlement more than 7,000 years ago. This new method allows accurate dating of other archaeological sites in southeastern Europe.

Researchers at the University of Bern have, for the first time, been able to precisely date the prehistoric settlement of early farmers in northern Greece more than 7,000 years ago. They achieved this by combining annual growth ring measurements on wooden building elements with a spike in cosmic 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 major role in archaeology. It is always necessary to know the age of a grave, settlement or single object. Determining the age of prehistoric finds has only been possible for a few decades. Two methods are used for this purpose: dendrochronology, which allows dating based on the sequence of annual rings in trees, and radiocarbon dating, which can calculate the approximate age of finds through the rate of radiocarbon isotope decay. ¹⁴C found in tree rings.

A team led by the Institute of Archaeological Sciences in University of Bern She has now succeeded in accurately dating timber from the archaeological site of Despilio in northern Greece, where dating by year was not previously possible, to various building activities between 5328 and 5140 BC. The researchers used high-energy particles from space, which can be reliably dated to 5259 BC. Their research was published May 20 in the journal Nature Communications.

Tree ring chronology and ¹⁴The C method has its limitations

Dendrochronology uses distinct patterns of broad and narrow annual growth rings in wood, which are influenced by climatic conditions. As a result, a log can be dated by comparing the width of the annual growth rings with an already existing standard or regional chronology.

“In Central Europe, there is a tree-ring chronology dating back approximately 12,500 years in the past – to 10,375 BC. However, this chronology only applies to certain regions. Archaeological University of Bern, “There is no fixed chronology for the Mediterranean region.”

Therefore, the dendrochronology of this area must be classified as “floating” using radiocarbon dating. As long as the tree is alive, it absorbs radioactive isotopes ¹⁴C (radiocarbon) present in the Earth’s atmosphere through Photosynthesis. When it dies, it is no longer absorbed ¹⁴C; The isotope decays with a half-life of 5,730 years. A laboratory measurement method can then be used to determine the quantity ¹⁴C is still present in a given tree ring, so the approximate time of tree death is calculated over its known half-life. “However, Accuracy “Such classifications are at best on the order of decades,” Maczkowski says.

Heap field in Dispilio. Nearly 800 piles, mostly made of juniper and oak, were sampled and measured for age. These data form the basis for the high-resolution dating of this site. Despilio is the first archaeological site to be dated to a specific year using the Miyake Event of 5259 BC. Credit: Dispilio paleontological archive

“Until recently, it was thought that dendrochronological dating of the year was only possible if a continuous regional tree-ring chronology was available, which is the case for prehistoric periods in only three regions worldwide: these are the southwestern United States, the northwestern United States “The foothills of the Alps and England/Ireland,” explains Albert Hafner, professor of prehistoric archeology at the University of Bern and senior author of the study.

A qualitative leap thanks to the Japanese physicist

In 2012, a solution to this problem emerged: Japanese physicist Fusa Miyake discovered that a massive influx of cosmic rays, most likely due to solar flares, could cause a slight increase in the atmosphere. ¹⁴C content, which is deposited in the rings of the tree of years in question. These increases can be accurately dated on the basis of long tree-ring chronologies, and because they are global events, they represent important anchor points, especially in regions that do not have consistent annual growth-ring chronologies.

“Miyake identified the first fulcrums of this kind, thus creating a paradigm shift in prehistoric archaeology,” says Albert Haffner. Today, dozens of these Miyake events Known until 12,350 BC, the two important events in 5259 and 7176 BC were only discovered in 2022 by researchers at ETH Zurich. Such events of similar magnitude have not been recorded in the past few centuries. If an event of this magnitude, as it did in 5259 BC, occurred today, it would likely have a catastrophic impact on communications and electronics.

Miyake event enables dating in Dispilio

The research team from the EXPLO project led by the University of Bern succeeded in establishing a chronology of the annual growth ring spanning 303 years, ending in 5140 BC, by analyzing 787 pieces of wood from the archaeological site of Despilio on Lake Oristida in northern Greece. . The identified settlement phases show various house building activities over a period of 188 years between 5328 and 5140 BC. This precise dating is possible because there was a known Miyake event during this period in 5259 BC.

Researchers at ETH Zurich were able to detect a significant rise in radiocarbon content during this time through radiocarbon dating of several individually identified annual growth rings. So it was a matter of reproducing this peak, which is globally reflected in the annual growth ring chronology of Siberian pine, American larch and European oak, in the annual growth ring chronology of Dysplio in Greece and linking it to the fixation point of 5259 BC. . “The Balkans are therefore the first region in the world to benefit from this paradigm shift and be able to successfully determine absolute date independently of a fixed calendar,” says Albert Haffner.

Andrzej Maczkowski adds: “We expect that other chronologies of the region from this period will now be linked to ‘Dispilio Chronology’ in rapid succession. This paves the way for the development of regional diachronology of the Southern Balkans.” The Balkans have the oldest lakeside settlements in Europe, dating back to Its sites date back to after 6000 BC. The region played a major role in the expansion of agriculture in Europe.

Reference: “Absolute dating of the European Neolithic using rapid 14C excursion in 5259 BC” by Andrzej Maczkowski, Charlotte Persson, John Francouz, Tryvon Giagkulis, Sonke Szydat, Lukas Wacker, Matthias Bolliger, Kostas Koutsakis and Albert Hafner, 20 May 2024, Nature Communications.
doi: 10.1038/s41467-024-48402-1