New method developed by University of Bristol researchers enables archeologists to directly date ancient pottery with precision using residual fats in the pores of the vessels.
Archeology, the scientific study of the material remains of ancient human life and activities, provides a window into ancient history and prehistory. One of the most challenging aspects for archeologists is dating the discovered objects. A team of scientists from the University of Bristol unveiled an innovative method to directly date archaeological pottery and published their peer-reviewed findings on April 8, 2020 in Nature.
Archeological dating methods are either direct or indirect. For direct or absolute dating, physiochemical analysis is conducted through methods such as thermoluminescence (light emissions from crystalline materials such as some minerals), dendrochronology (the study of annual growth rings in tree trunks), or radiocarbon dating.
In contrast, indirect or relative dating, uses contextual data such as typology, the comparing similarity of reference objects, or stratigraphy, the analysis of surrounding geographic rock layers, or strata.
Out of all these methods, the most common method of dating organic materials in archaeology is radiocarbon dating. Radiocarbon dating is a relatively new concept that was proposed in 1946 by Willard Libby, a professor of chemistry at the University of Chicago who was later awarded the Nobel Prize in Chemistry in 1960 for his method of using carbon-14 (radiocarbon) for determining age for archeology, paleontology, geophysics, geology, and other branches of science.
In the Earth’s atmosphere, carbon fluctuates over time. Carbon-14 is formed when atmospheric nitrogen-14 interact with neutrons from cosmic rays. Through photosynthesis, plants, and certain organisms such as cyanobacteria (group of photosynthetic bacteria) and algae, take in light and convert it into chemical energy. In photosynthesis, solar energy is used to convert water and carbon dioxide into oxygen and glucose, a simple sugar.
When animals and humans ingest plants, the carbon is further distributed in the food cycle. When these organisms die, it stops absorbing carbon-14. Over time, the amount of carbon-12 will remain steady. In contrast, the amount of carbon-14 will decrease over time at a constant rate, with a half-life of 5,730 ± 40 years. This means that given a set of carbon-14 atoms, it will take 5,730 years for half to decay.
Radiocarbon dating of ancient pottery presents a unique challenge. For example, there may be many various carbon sources with different radiocarbon ages found in the pottery artefacts. Professor Richard Evershed from the University of Bristol's School of Chemistry led the team of researchers in creating a method to accurately date the food residues protected within the pores of the pottery via accelerator mass spectrometry analysis of carbon-14 for two common fats— palmitic and stearic fatty acids.
Both palmitic and stearic fats are commonly found in nature. Palmitic fatty acid is a saturated fat found naturally in meat, milk, butter, cheese, and palm oil. Stearic fatty acid, also a saturated fat, is a waxy, solid found in cocoa butter, animal fats, shea butter, and vegetable fats. In the study, the scientists purified
The University of Bristol researchers extracted palmitic and stearic fatty acids from the pottery that were purified by preparative gas chromatography, then used accelerator mass spectrometry to perform radiocarbon (carbon-14) dating.
Accelerator mass spectrometry radiocarbon dating is a powerful and sensitive technique. It has the ability to perform with small samples such as blood particles or grains, and is not only used in archaeology, but also in many other purposes such as pharmacokinetics, toxicology, and metabolite profiling.
Next, the researchers applied this method to fat extracts from Neolithic pottery artefacts that were up to 8,000 years old with previously known accurate dating for archaeological sites in Britain, Africa, and Europe. The pottery came from sites that included the World Heritage site of Çatalhöyük in central Turkey, the rock shelter site of Takarkori in Saharan Africa, the Sweet Track site in Somerset (county in South West England), the Principal Place in Shoreditch (East End of London), the northern and western parts of the LBK (Linearbandkeramik—Linear Pottery Culture) oecumene, and various sites throughout the Alsace region of France.
“We present accurate compound-specific radiocarbon determinations of lipids extracted from pottery vessels, which were rigorously evaluated by comparison with dendrochronological dates and inclusion in site and regional chronologies that contained previously determined radiocarbon dates on other materials,” wrote the researchers in the study.
The scientists point out that the compound-specific dates from each of the palmitic and stearic fatty acids in pottery vessels provide “an internal quality control of the results and are entirely compatible with dates for other commonly dated materials.”
Pottery is one of the more frequently discovered objects from archaeological sites, and it provides important clues to understanding how people lived thousands of years ago. One of the oldest of human innovation is pottery. Prehistoric pottery fragments dating back 20,000 years ago during the Old Stone Age (Paleolithic) were discovered in Xianrendong Cave in Jiangxi Province, China. With this innovative method of dating pottery vessels, archeologists have a reliable way to directly date pottery, providing a window to the ancient history of humanity.
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