Calibration and radiocarbon dating
However, to calibrate shell dates, there are some additional steps.
If the shell samples are all marine in origin, you must use the Marine (marine98.14c) dataset for calibrating these samples.
For example, rootlet intrusion, soil type (e.g., limestone carbonates), and handling of the specimens in the field or lab (e.g., accidental introduction of tobacco ash, hair, or fibers) can all potentially affect the age of a sample.
Bioturbation by crabs, rodents, and other animals can also cause samples to move between strata leading to age reversals.
Let's say that you have considered all of the potential dating and sampling issues.
You have sent your samples off to the lab and received the results back. Because the date is only the conventional age, you need to transform it to calendar years by using a calibration program. CALIB 4.4 These figures tell you that the most likely age of your sample is between AD 13 (a 96.3% chance). It is also possible (though not very likely) that the sample dates to the period between AD15 (3.6%) or AD13 (0.1%).
Select the Probability Distribution option, and then click on Make Another Plot .
These instructions, as noted above, can be used to calibrate the Conventional Age for any wood charcoal sample.
The surrounding environment can also influence radiocarbon ages.A benefit of using Ox Cal is that the graphs are easier to interpret and to use in presentations, although as far as your instructor is concerned, the software itself is not as intuitive to use as CALIB.Ox Cal 3.9v Let's use Ox Cal v.3.9 to calibrate a sample from Trinidad (OS-49084) using the terrestrial (intcal98.14c) dataset option. File: Analysis Options Choose your "Reporting" option (e.g., BP or BC/AD) Choose your sigma "Range" Click "Browse" and select the appropriate Radiocarbon Calibration Curve (e.g., intcal98.14C for terrestrial samples or marine98.14C for marine samples).Desmond Clark (1979:7) observed that without radiocarbon dating "we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation." And as Colin Renfrew (1973) aptly noted over 30 years ago, the "Radiocarbon Revolution" transformed how archaeologists could interpret the past and track cultural changes through a period in human history where we see among other things the massive migration of peoples settling virtually every major region of the world, the transition from hunting and gathering to more intensive forms of food production, and the rise of city-states.However, as with any dating technique there are limits to the kinds of things that can be satisfactorily dated, levels of precision and accuracy, age range constraints, and different levels of susceptibility to contamination.