The year 2025 saw several notable archaeological discoveries in Peru, Belize, Egypt, and Wales. Among all the discoveries, the most fascinating is the Caral-Supe civilization in Peru’s Supe Valley, which is 3,800 year old. When archaeologists discover ancient civilizations, human remains, or even artifacts, they want to estimate their age. Identifying the age of an archaeological site is important for historical timelines, understanding who created it, how it was created and used, and the wider social structures and cultures. For example, the state-of the art sewage system of Mohenjo-Daro in the Indus valley, including private toilets and brick-lined drains, provides design principles that later inspired others.
Archaeologists adopt broadly two methods to estimate the age of ancient remains: relative dating and absolute dating. Relative dating estimates whether one layer of earth or artifact is older or younger than another without providing estimated dates. Absolute dating identifies the specific chronological age of a site, a human remains, or an artifact, sometimes in years before the present.
Relative Dating
Relative dating is the foundational method that archaeologists use to sequence artifacts without any estimated dates. It is useful for initial assessments. One of the techniques in this category is stratigraphy, which looks at soil layers (strata) at a site. Deep layers are generally older than upper layers, assuming no external events like earthquakes or human activity. Artifacts located in the same layer are considered to be contemporaneous. Another technique is called seriation, in which archaeologists group artifacts based on their style, material or frequency and arranged chronologically by applying statistical techniques. For example, changes in poetry designs over a period can develop a sequence revealing cultural changes. The third type is cross-dating, in which artifacts of one site are compared to the artifacts of a dated site elsewhere. If artifacts are similar in both sites there relative ages can be predicted.
These techniques are not without limitations. Firstly, they are subjective and can lead to errors. For instance, artifacts can transfer to different layers due to earthquakes and human activities. These techniques do not inform exact estimated ages, making them less powerful than absolute techniques.
Absolute Techniques
Absolute techniques are scientific methods that estimate the age of an artifact based on physical and chemical changes. A most common method is radiocarbon dating or Carbon-14. It measures the decay of Carbon-14 (a radioactive isotope of carbon) in organic materials (bones, wood, or charcoal), providing an estimated age of items 50,000-60,000 years old. However, this method is not without limitations. Based on 2022 cost estimates, it is costly, €25,000 or $27,000 per curie. The Russia-Ukraine conflict increased the price further because Russia is the major producer of Barium used in Carbon-14. New facilities are being established in China and Canada, which will stabilize the supply of Barium. Additionally, this method is inapplicable to inorganic materials, like stones or metals. There are other absolute dating methods, but each has a certain use.
A visual summary of absolute dating methods and their strengths
Which method is the best?
Both methods are complementary rather than supplementary. Applying reactive techniques in the initial assessment, such as stratigraphy to estimate layers and then using Carbon-14 to predict the age of artifacts, is the best approach. New technology, such as an accelerator mass spectrometer for Carbon-14, reduced the need of large samples and improve accuracy.
To summarize, absolute methods like Carbon-14 are superior because they precisely estimate age but other techniques cannot be completely disregarded. Using both broader techniques helps to uncover past civilizations like the innovative drainage of Mohenjo-Daro to the pyramids of Caral.
