Chronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "dating method". Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history, archaeology, geology, paleontology, astronomy and even forensic science, since in the latter it is sometimes necessary to investigate the moment in the past in which the death of a cadaver occurred.
Relative dating methods are unable to determine the absolute age of an object or event, but can determine the impossibility of a particular event happening before or after another event of which the absolute date is well known. In this relative dating method, Latin terms ante quem and post quem are usually used to indicate both the oldest and the most recent possible moments when an event occurred or an artifact was left in a stratum. But this method is also useful in many other disciplines. Historians, for example, know that Shakespeare's play Henry V was not written before 1587 because Shakespeare's primary source for writing his play was the second edition of Raphael Holinshed's Chronicles, not published until 1587. Thus, 1587 is the post quem dating of Shakespeare's play Henry V. That means that the play was without fail written after (in Latin, post) 1587.
The same inductive mechanism is applied in archaeology, geology and paleontology, by many ways. For example, in a stratum presenting difficulties or ambiguities to absolute dating, paleopalynology can be used as a relative referent by means of the study of the pollens found in the stratum. This is admitted because of the simple reason that some botanical species, whether extinct or not, are well known as belonging to a determined position in the scale of time.
For a non-exhaustive list of relative dating methods and relative dating applications used in geology, paleontology or archaeology, see the following:
Absolute dating methods, by using absolute referent criteria, mainly include the radiometric dating methods. Some examples of both radiometric and non-radiometric absolute dating methods are the following:
Same as geologists or paleontologists, archaeologists are also brought to determine the age of ancient materials, but in their case, the areas of their studies are restricted to the history of both ancient and recent humans. Thus, to be considered as archaeological, the remains, objects or artifacts to be dated must be related to human activity. It is commonly assumed that if the remains or elements to be dated are older than the human species, the disciplines which study them are sciences such geology or paleontology, among some others.
Nevertheless, the range of time within archaeological dating can be enormous compared to the average lifespan of a singular human being. As an example Pinnacle Point's caves, in the southern coast of South Africa, provided evidence that marine resources (shellfish) have been regularly exploited by humans as of 170,000 years ago. On the other hand, remains as recent as a hundred years old can also be the target of archaeological dating methods. It was the case of an 18th-century sloop whose excavation was led in South Carolina (United States) in 1992. Thus, from the oldest to the youngest, all archaeological sites are likely to be dated by an appropriate method.
Dating material drawn from the archaeological record can be made by a direct study of an artifact, or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. Dating is carried out mainly post excavation, but to support good practice, some preliminary dating work called "spot dating" is usually run in tandem with excavation. Dating is very important in archaeology for constructing models of the past, as it relies on the integrity of dateable objects and samples. Many disciplines of archaeological science are concerned with dating evidence, but in practice several different dating techniques must be applied in some circumstances, thus dating evidence for much of an archaeological sequence recorded during excavation requires matching information from known absolute or some associated steps, with a careful study of stratigraphic relationships.
In addition, because of its particular relation with past human presence or past human activity, archaeology uses almost all the dating methods that it shares with the other sciences, but with some particular variations, like the following:
Seriation is a relative dating method (see, above, the list of relative dating methods). An example of a practical application of seriation, is the comparison of the known style of artifacts such as stone tools or pottery.
The stratigraphy of an archaeological site can be used to date, or refine the date, of particular activities ("contexts") on that site. For example, if a context is sealed between two other contexts of known date, it can be inferred that the middle context must date to between those dates.
The results provide a compelling case for applicability of amino acid racemization methods as a tool for evaluating changes in depositional dynamics, sedimentation rates, time-averaging, temporal resolution of the fossil record, and taphonomic overprints across sequence stratigraphic cycles.
A team from the University of Manchester and the University of Edinburgh has discovered a new technique which they call 'rehydroxylation dating' that can be used on fired clay ceramics like bricks, tile and pottery.