These new standards allow to date with unprecedented precision findings that go back to 55,000 years ago.
The outstanding work of an international research group allowed to significantly improve the accuracy of the calibration curve of radiocarbon dating, eventually providing high levels of precision in dating objects as old as 55,000 years. The University of Bologna is a member of this research group which has worked on this project for seven years and analysed more than 15 thousand findings.
The journal Radiocarbon published this project's results, which consist of three new radiocarbon calibration curves: IntCal20 for findings coming from the northern hemisphere, SHCal20 for the southern hemisphere and Marine20 for the oceans.
Representing the University of Bologna in this research group is Sahra Talamo, professor at the Chemistry Department "Giacomo Ciamician" and Principal Investigator of the ERC RESOLUTION project, which aims at developing high-resolution radiocarbon dating datasets able to shed light on key-periods of the European Prehistory.
"These new radiocarbon calibration curves will allow to observe the past with an unprecedented level of detail", explains Professor Talamo. "For example, through these curves, we will be able to collect information on momentous periods in the history of Homo Sapiens: how they came to Europe, their interactions with Neanderthals and when these two species overlapped in different European areas".
Radiocarbon-based techniques play a fundamental role in the development of many research fields. Not only within archaeology, allowing for the precise dating of the most ancient (pre)historical findings; but also within geosciences, in this case, radiocarbon dating allows to retrace climate changes over long periods, thus providing insights into future climate changes.
"Radiocarbon dating has been a revolution within the fields of archaeology and environmental sciences", confirms Paula Reimer, head of this international research group (IntCal Working Group) and professor at Queen's University Belfast (UK). "Improving calibration curves implies better knowledge of our history: this update of radiocarbon dating standards is fundamental for answering some pressing questions about the evolution of the world we live in, and the role played by humans in this process".
The method of radiocarbon dating was developed in 1949 by Willard Frank Libby, who received the Nobel Prize in Chemistry for his work in 1960. It is based on two carbon isotopes, one is stable (Carbon-12) and one is radioactive (Carbon-14).
During their life, plants and animals acquire carbon in the form of CO2. This means that they have the same proportion of Carbon-12 and Carbon-14 as the atmosphere in which they live. Once they die, they cease to acquire carbon. As this happens, stable Carbon-12 isotopes remain unchanged, while radioactive Carbon-14 isotopes will start to decay at a precise and known rate. Because Carbon-14 decays at a known rate, measuring its levels in an organic sample will tell us when that plant or animal died and, thus, its age. Until today, this method allowed to date objects back to 50,000 years ago, now for the first time, with the new calibration curve scientists can go back in time up to 55,000 years.
However, there is a complication. The quantity of Carbon-14 in the atmosphere has not been even throughout history, meaning that Carbon-14 age is not identical to calendar age. The procedure of calibration was devised to overcome this problem. Indeed, it allows to calibrate Carbon-14 age against an absolute time scale: this is how they came up with the IntCal curve (Internal Calibration Curve).
Scientists developed the new IntCal20, which is very precise, to produce trustworthy timelines of paleoenvironmental change and to gather a better understanding of climate events’ sequences. More detailed analyses of Carbon-14 in findings from a number of archives allowed to obtain the results that populate the calibration curve. Among these findings, there are 14,000-year-old trees, stalagmites retrieved in different caves, coral from the sea and cores of lake and ocean sediments. To build the new calibration curves, the IntCal Working group carried out 15 thousand radiocarbon measurements on objects dating back up to 55,000 years ago.
"Thanks to the high-resolution of the sampling, the new calibration curves allow researchers to obtain 10-years dating that go back in time up to 55,000 years. Compared to what was possible just until yesterday, this is a significant improvement", says Professor Talamo. "This is however a first step to reach a precise timeline of the events characterizing human evolution. Hence, the importance of the RESOLUTION project: using fossil trees and exploiting Beryllium-10 and Carbon-14 synchrony (as evident from IntCal20 in the period spanning from 14,000 to 14,700 years ago), researchers will obtain a more precise curve and, for the first time, an exceptionally high resolution of the European Prehistory".