Scientists reveal new curves to enhance dating

Radiocarbon dating is set to become more accurate after a team of scientists improved the technique for assessing the age of historical events and objects. Three researchers at UNSW Sydney, in collaboration with international colleagues, measured 15,000 samples from objects dating back as far as 55,000 years ago, as part of a seven-year project. They used the measurements to create new international radiocarbon calibration (IntCal) curves. UNSW project lead Professor Chris Turney described radiocarbon dating as the workhorse of archaeological and environmental science. “Radiocarbon dating helps us understand so many different aspects of the environment," he said. "This is especially important in Australia as the driest inhabited continent on the planet. For instance, as part of the ARC Centre of Excellence in Australian Biodiversity and Heritage (CABAH), we’re looking at human migration and adaption in Australia during multiyear-long droughts known as megadroughts. "Working with colleagues, we’re interrogating fossil records of megafauna to try to understand when and why they went extinct. Radiocarbon dating helps the scientific community bring the timing of these different elements together, which gives us a better sense of where we might be going.” For this update, the team of researchers developed three curves, published this week in Radiocarbon: IntCal20 for objects found in the Northern Hemisphere, SHCal20 for the Southern Hemisphere, and Marine20 for the world’s oceans. Advanced measurement brings increased precision The curves are created based on collecting a huge number of archives which store past radiocarbon but can also be dated using other methods. Such archives include tree-rings from preserved logs in bogs, stalagmites found in caves, corals from the sea and cores drilled from lake and ocean sediments. Previous versions of the radiocarbon calibration curve that were periodically compiled over the past 50 years were heavily reliant on measurements taken from blocks of wood containing 10 to 20 years of growth so they were big enough to be tested for radiocarbon. Advances in radiocarbon measurement mean the updated curves instead use tiny samples, such as tree-rings covering just single years, providing previously impossible precision and detail in the new calibration curves. Additionally, improvements in understanding of the carbon cycle have meant the curves have now been extended all the way to the limit of the radiocarbon technique, to 55,000 years ago. The new curves were a collaboration between 41 institutions across 14 countries. Radiocarbon dating – first developed in 1949 – depends on two isotopes of carbon called stable 12C and radioactive 14C. While a plant or animal is alive it takes in new carbon, so has the same ratio of these isotopes as the atmosphere at the time. But once an organism dies it stops taking in new carbon – so the stable 12C remains but the 14C decays at a known rate. By measuring the ratio of 14C to 12C left in an object, we can estimate the date of its death. “If the level of atmospheric 14C were constant, this would be easy,” Professor Chris Turney explains. “However, it has fluctuated significantly through the past. In order to date organisms precisely scientists need a reliable historical record of its variation to accurately transform 14C measurements into calendar ages. The new IntCal curves provide this link.” The UNSW contribution to the research was completed at the Chronos 14Carbon-Cycle Facility that was officially opened in November 2019. The facility contains the only MIni CArbon Dating System (MICADAS) in the Southern Hemisphere. Researcher Dr Adam Sookdeo at work in the Chronos 14Carbon-Cycle Facility. Photos courtesy UNSW Sydney

Scientists reveal new curves to enhance dating

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