Visitors engage with technology-enhanced archaeology at the 2025 Beijing–China International Cultural Heritage Expo at Liulichang Cultural Street in Beijing on Nov. 21, 2025. Photo: IC PHOTO

Contemporary archaeology places strong emphasis on integrating multidisciplinary evidence. Diverse forms of data—including archaeological stratigraphy, typological sequences, zooarchaeology and archaeobotany, environmental reconstruction, and materials analysis—must ultimately be situated on a shared timeline. The introduction of SAAR dating has made it considerably easier to pinpoint the precise timing of key turning points in social evolution.

At the molecular level, SAAR dating also enhances the comparability of cross-regional studies. Dietary reliance on aquatic resources varies widely across regions, and direct comparisons based on bulk collagen dating risk misreading “dietary disparities” as “temporal differences.” By reducing the influence of carbon reservoir effects and contamination, SAAR dating allows data from different regions to align more closely with a unified temporal standard.

The project to trace the origins of Chinese civilization—centered on themes of unity in diversity, regional interaction, and pathways of innovation—demands robust and reliable chronological coordinates. Using smaller molecules to illuminate broader historical narratives has thus become one of the most meaningful directions in the development of archaeological science in contemporary China.

From ‘collagen’ to ‘amino acids’

The material long regarded as the “gold standard” for radiocarbon dating of bones is collagen. Traditional approaches extract and purify whole collagen before converting it into a sample for dating. Yet if the collagen is contaminated by soil humic acids, preservation solutions, or adhesive repair materials, or if it incorporates carbon from different sources—such as the “old carbon” signal associated with heavy consumption of aquatic resources—the resulting date may deviate from the true age.

SAAR dating addresses these problems by refining radiocarbon analysis to the molecular level. In this method, collagen is first hydrolyzed into amino acids, after which a specific amino acid is isolated through chromatographic techniques and dated independently. This technique offers far greater resistance to contamination: many external organic contaminants do not enter the sample in the form of the target amino acid, and even when they do, they are more readily removed during separation and purification.

Different amino acids also follow distinct metabolic pathways within an organism. Essential amino acids, which are derived primarily from dietary proteins, can in principle trace the true input of the food web more accurately and are especially suitable for micro-samples. With advances in accelerator mass spectrometry (AMS) enabling reliable measurement of extremely small carbon samples, the strategy of achieving precision through minimalism—dating single amino acids—has gradually become feasible in practice.

Removing ‘older carbon’ bias

In aquatic environments, inorganic carbon does not always update in step with atmospheric carbon, resulting in the presence of “older” carbon in most forms of aquatic food. When people consume fish, shellfish, or other freshwater organisms, this older carbon is incorporated into their bodies, affecting the radiocarbon dates of human remains. Such issues are particularly common at coastal shell middens, in river and lake basins, and at sites characterized by strong fishing and gathering traditions.

Within the same time period, individuals who consumed different proportions of aquatic food can yield divergent results when dated using traditional collagen methods, sometimes producing a systematic bias toward older ages. These errors directly affect interpretations of core archaeological questions, including the pace of settlement emergence, the speed of social differentiation, and the sequence of technological diffusion.

From a metabolic perspective, some amino acids are resynthesized in the body from multiple carbon sources, making them prone to “carbon mixing,” whereas certain essential amino acids depend more directly on dietary input. The degree to which different food sources interfere with dating results can also be assessed using stable isotope analysis.

In practice, amino acids can first be grouped into “high-risk” and “low-risk” categories according to their susceptibility to aquatic carbon signals, based on molecular-level isotopic evidence. By selecting amino acids from the low-risk group as targets for radiocarbon dating, researchers can significantly reduce the chronological bias introduced by carbon reservoir effects.

Expanding boundaries of dating

Many archaeological sites in southern China face even greater dating challenges due to environmental conditions. Acidic soils and warm, humid climates promote intense microbial activity, leading to extensive degradation of bone collagen. As a result, excavations in the region often recover skeletal remains for which usable collagen is nearly absent, making conventional radiocarbon dating difficult or impossible.

A common response has been to date substitute materials from the same stratigraphic layer—such as charcoal, plant seeds, or other organic remains—or to rely on indirect evidence to establish a chronological range. Yet when research focuses on human migration, ethnic interaction, or changes in social structure, directly dating human bones remains irreplaceable, as it corresponds most closely to the lifetime of individuals.

SAAR dating not only produces a numerical age estimate but also provides a clear account of why that estimate is credible and where uncertainties may still lie. For major national research initiatives such as the project to trace the origins of Chinese civilization, which address both scholarly audiences and the broader public, this transparency and traceability are especially crucial.

It must be acknowledged, however, that under conditions of extreme acidity where collagen has completely disappeared, SAAR dating also encounters limitations. It is not a universal solution for all bone samples from the southern parts of China. Even so, the method substantially expands the boundaries of what can be dated and offers clearer criteria for distinguishing between what is datable and what is not.

Li Zihan is a distinguished research fellow from the Institute of Archaeology, Museology and Chinese Civilization at Nanjing University.