- The first and often most important step in archaeological research involves placing things into sequence, or dating them relative to each other. Through relative dating methods archaeologists can determine the order in which a series of events occurred, but not when they occurred. Stratigraphy is a key factor in relative dating because a sequence of sealed deposits results in the formation of a relative chronology. Relative dating can also be done through typology. Typological sequencing assumes that artifacts of a given time and place have a recognizable style and that change in this style is gradual and evolutionary over time.
- To know how old sequences, sites, and artifacts are in calendar years, absolute dating methods must be used. Absolute dating relies on regular, time-dependent processes. The most obvious of these, the rotation of the earth around the sun, has been and is the basis for most calendar systems. In literate cultures, historical chronologies can often be used to date sites and objects.
- Before the advent of radioactive dating methods, varves (annual deposits of sediments) and dendrochronology (tree-ring analysis) provided the most accurate means of absolute dating. Today, however, radiocarbon is the single most useful dating method. Atmospheric radiocarbon is passed on uniformly to all living things, but since this uptake of radiocarbon ceases at death, the isotope then begins to decay at a steady rate. The amount of radiocarbon left in a sample thus indicates the sample’s age. Because atmospheric radiocarbon levels have not always been constant, a radiocarbon date must be calibrated to arrive at a true calendar date.
- For the Paleolithic period, beyond the scope of radiocarbon dating, potassium-argon (or argon-argon) and uranium-series dating are the most useful techniques. Other dating methods are available, such as thermoluminescence and electron spin resonance, but these tend to be either less precise or suitable only in special circumstances.
- A promising avenue for future work in chronology is the correlation of different dating methods. One of the most powerful ways of establishing correlation between sequences is through the occurrence of geological events on regional or even global scales; volcanic eruptions are a good example.
Key Concept Identifications
Relative dating, p.132
Battleship curve, p.135
Climate and Chronology
Deep-sea cores, pp.137–38
Ice cores, pp.137–38
Pollen dating (palynology), p.138
Absolute dating, p.138
Calendars and Historical Chronologies
Maya Calendar, pp.140–41
Terminus post quem, p.142
Terminus ante quem, p.142
Annual Cycles: Varves and Tree-Rings
Floating chronology, p.145
Radiocarbon dating, pp.146–55
Principles of radioactive decay, p.147
Accelerator mass spectrometry (AMS), p.148
Potassium-argon dating, pp.155–56
Uranium-series dating, pp.156–57
Fission-track dating, pp.157–58
Other Absolute Dating Methods
Thermoluminescence dating, pp.160–62
Optical dating, p.162
Electron spin resonance dating, p.162
Genetic dating, pp.162–63
Calibrated Relative Methods
Amino-acid racemization, p.163
Archaeomagnetic dating, pp.163–64
Geomagnetic reversals, pp.163–64
"Out of Africa" expansion, p.167