A pile of human bones in Chauchilla, an ancient cemetery in the desert of Nazca, Peru.
Researchers in Italy have combined the power of near-infrared hyperspectral imaging (NIR-HIS) spectroscopy with chemometrics to create a new non-destructive radiocarbon dating method they say can “revolutionize the field of archeology.”
The new technique makes it possible—for the first time—to precisely quantify and map the presence of collagen, the invisible protein that is essential for estimating radiocarbon dates.
“Our results will offer significant advances for the study of human evolution,” says Sahra Talamo co-author of the study and director of the radiocarbon dating lab BRAVHO at the University of Bologna. “We will be able to minimize the destruction of valuable bone material, which is under the protection and enhancement of European cultural heritage and thus allow us to contextualize the valuable object by providing an accurate calendar age.”
Today’s radiocarbon dating is extremely accurate, but has some limitations. First and foremost, it is destructive—which is not an ideal quality when sampling rare prehistoric bones that are considered part of cultural history. Additionally, because of the diagenetic alteration of collagen over time, large starting weights of bones—at least 500 mg—are necessary to extract sufficient collagen for accelerator mass spectrometry (AMS) 14C dating. However, most recovered archeological bones are small—often less than 200 mg of bone material. They are also invaluable historical objects.
The new method addresses both those limitations, as it enables researchers to determine not only the amount of collagen still contained in a bone sample, but the location of the collagen as well.
“This new technique allows not only selecting the best specimens but also choosing the sampling point in the selected ones based on the amount of collagen predicted,” said Paolo Oliveri co-author of the paper and professor at Genoa University. “This method helps to drastically reduce the number of samples destroyed for 14C analysis, and within the bone, it helps to avoid the selection of areas that may present a quantity of collagen not sufficient for the dating. This increases the preservation of precious archaeological materials.”
The NIR-HIS used in the study, which is published in Communications Chemistry, is a line-scan (push-broom) system that acquires chemical images in which, for every pixel, a full spectrum in the 1,000–2,500 nm spectral range (NIR) is recorded. Additionally, the system can analyze a single bone sample in just a few minutes, saving laboratory time and money.
The first-time combination of NIR-HIS with a regression model gave the scientists the flexibility to examine the whole sample for average collagen content, as well as localize analysis to small areas—including single points. The combo system quantifies the collagen at every pixel, generating accurate quantitative chemical maps at a high spatial resolution of about 30 µm.
“As far as radiocarbon is concerned, we could strategically sample bones of high patrimonial value,” said Talamo. “For example, knowing the precise amount of collagen concentrated in a precise area of the bone allows us to cut only this portion. Moreover, when the prediction of collagen shows that the bone was poorly preserved, we can decide to perform a soft 14C pretreatment to minimize collagen loss during the extraction.”
The Italian research team says their new technique is well-suited to re-analyze bone samples from many archeological sites where previous attempts at radiocarbon analysis were not successful because of poor preservation.