Radiocarbon dating, invented in the late 1940s and improved ever since to provide more precise measurements, is the standard method for determining the dates of artifacts in archaeology and other disciplines. But this method isn’t perfect , some fine-tuning is needed.

“If it’s organic and old – up to 50,000 years – you date it by radiocarbon,” said Sturt Manning, the Goldwin Smith Professor of Classical Archaeology in the College of Arts and Sciences.

Manning is lead author of a new paper that points out the need for an important new refinement to the technique. The outcomes of his study, published March 18 in Science Advances , have relevance for understanding key dates in Mediterranean history and prehistory, including the tomb of Tutankhamen and a controversial but important volcanic eruption on the Greek island of Santorini.

What is Radiocarbon Dating?

Radiocarbon dating measures the decomposition of carbon-14, an unstable isotope of carbon created by cosmic radiation and found in all organic matter. Cosmic radiation, however, is not constant at all times. To account for fluctuations of cosmic radiation in the Earth’s atmosphere, the radiocarbon content of known-age tree rings was measured backward in time from the 20th century, for thousands of years.

Tree-ring calibrated radiocarbon started to be widely used 50 years ago. A standard calibration curve was introduced in 1986 and is updated every few years as more data are added.

“A single Northern Hemisphere calibration curve has formed the basis of radiocarbon dating in Europe and the Mediterranean for five decades, setting the time frame for prehistory,” Manning and co-authors write. “However, as measurement precision increases, there is mounting evidence for some small but substantive regional (partly growing season) offsets in the same-year radiocarbon levels.”

Radiocarbon Needs Refining

In their study, Manning and co-authors question the accuracy of a single calibration curve for all of the Northern Hemisphere. Using data collected by only one lab to control for interlaboratory variation, they compared radiocarbon data from northern Europe (Germany) and from the Mediterranean (central Turkey) in the 2nd and 1st millennia BC. They found that some small but critical periods of variation for Mediterranean radiocarbon levels exist. Data from two other radiocarbon labs on samples from central Italy and northern Turkey then provided consistency.

Growing seasons play a role, the paper says. The radiocarbon level on Earth varies according to the season; there’s a winter low and a summer high, Manning said. The carbon in a tree ring reflects when the tree was photosynthesizing and, therefore, taking carbon out of the atmosphere.

The carbon in a tree ring reflects when the tree was photosynthesizing and, therefore, taking carbon out of the atmosphere. ( Pixabay License )

“In northern Europe or in North America, a tree is going to be doing this in April through September. But a tree in Jordan or Israel does that October through April – almost the opposite time of the year,” he said.

In 2018, Manning noted “scholars working on the early Iron Age and Biblical chronology in Jordan and Israel are doing sophisticated projects with radiocarbon age analysis, which argue for very precise findings. This then becomes the timeline of history. But our work indicates that it's arguable their fundamental basis is faulty -- they are using a calibration curve that is not accurate for this region.”

Sturt Manning cores a multi-century old Juniperus phoenicea tree near Petra in southern Jordan. ( Cornell University )

These variations, although small, potentially affect calendar dates for prehistory by up to a few decades, the paper concludes.

Special Significance for Dating Key Historical Moments

Even small date offsets – 50 years or less – are important for building the timeline of the Mediterranean region, which, in the last two millennia BC, was a hotbed of interrelated cultures.

The adjusted dates confirm previously awkward timelines, where radiocarbon and history did not seem to agree for some historical landmarks, including the death and burial of Egyptian pharaoh Tutankhamen , which is dated around the 1320s to 1310s BC, according to recent Egyptology.

Howard Carter and associates opening the shrine doors in the burial chamber of Tutankhamen’s tomb. ( Public Domain )

The study also addresses a debate over the date of a massive volcanic eruption on Santorini. This much-studied event is dated around 1500 BC by archaeologists but earlier – 1630 to 1600 BC – by scientists. Manning said the new findings rule out the date of 1500 BC, but may also modify the science.

A 1630–1600 BC date remains possible, but a later date in the range of 1600-1550 BC now becomes plausible, and even works better with existing archaeological and historical records, including writings from Egypt.

Hypothetical calendar dating probability estimates for the Santorini/Thera volcanic destruction level from the study’s data and models. ( Manning et al. 2020 )

The study also has ramifications for understanding which culture influenced the Minoans and Mycenaeans, which led to ancient Greece.

“Getting the date right will rewrite and get our history correct in terms of what groups were significant in shaping what then became classical civilization,” Manning said. “An accurate timeline is key to our history.”

He predicts follow-up on this study and a future with more specific regional calibration curves within the Northern Hemisphere – as well as subsequent adjustment to historical dates.

Top Image: Radiocarbon dating needs fine-tuning if scientists and archaeologists want a more accurate historical timeline. Source: Elnur /Adobe Stock

This article is a press release by Cornell University originally titled, ‘Fine-tuning radiocarbon dating could ‘rewrite’ ancient events’ posted on EurekAlert! It has been edited for content and length.