Since its creation in 1960, radiocarbon dating has been used to determine the age of anything from books and skeletons to mummies and trafficked ivory. Now, this system will be recalibrated with the inclusion of thousands of data obtained since its last version, in 2013.
“A new calibration curve is of fundamental importance for understanding hominid prehistory and chronology,” says archeological chronologist and director of the Oxford Radiocarbon Accelerator Unit, Tom Higham.
This adjustment is being made not only to better understand the past, but to compensate for the present, which today dumps billions of tons of carbon into the environment. Burning fossil fuels and testing nuclear bombs radically changed the amount of carbon-14 in the air.
Pollution alters the balance
Almost 99% of all the Earth’s carbon is in the form of its isotope with 12 neutrons at its core; carbon-12 is the most stable form of the element. The radiocarbon dating technique measures the presence of an unstable isotope and is therefore much rarer: carbon-14, which in nature is produced at a constant rate in the Earth’s upper atmosphere.
When a plant or animal dies, it stops absorbing that isotope, and what has accumulated begins to decay. Measuring the remaining amount provides an estimate of how long ago something died.
The problem is that humanity, especially in the last few decades, has released carbon from fossil fuels into the atmosphere, which no longer have a measurable amount of carbon-14. The result is that billions of tons of carbon-12 artificially put on the scale are ruining the constant ratio between the two isotopes.
Trees keep a reliable calendar
To produce a curve that can be used to relate calendar years to those determined by radiocarbon, a sequence of samples with a known date is necessary, such as the rings on a tree trunk. Scientists use this method combined with information from lake and ocean sediments, corals and stalagmites to calibrate the system.
Since 1998, the IntCal (IntCal98) system has been used, which has already undergone three updates: in 2004, 2009 and 2013. Now, the 2020 version is being launched, with new curves for the Northern (IntCal20) and Southern (SHCal20) hemispheres and more for marine samples (MarineCal20).
IntCal20 is based on 12,904 data points, almost twice the size of the 2013 data set. This made, for example, the dating of a Homo sapiens jaw found in 2002 at Pe? Tera cu Oase (Or a Cave with Bones) in Romania.
There, the oldest remains of modern humans (between 35 and 40 thousand years) were excavated. The age of the specimen called Oase 1 was reassessed by the new curve; he is hundreds of years older than previously thought. Genetic analyzes even revealed that he had a Neanderthal ancestor, four to six generations away.
“This means that the older Oase 1 is, the more Neanderthals roamed Europe,” explains Higham. In contrast, the teenager whose fossils were unearthed in Siberia lived a thousand years ahead of what was thought and this, according to the chronologist, changes the story of the arrival of modern humans in Siberia.