In most publications the raw radiocarbon age should be reported as well as the calibrated age range.Our reporting process includes an automatic attempt at calibrating your radiocarbon result with an internationally agreed calibration curve.Radiocarbon ages are not the same as calendar time due to past fluctuations of carbon-14 in the atmosphere.Calibration is necessary to convert radiocarbon ages into calendar equivalents (calibrated ages).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.Since that time the calibration datasets have continued to be extended and improved. For Southern Hemisphere samples SHCal04 is available back to 11,000 cal BP (Mc Cormac et al., 2004).The Int Cal working group established a set of criteria for calibration datasets (Reimer et al. The current calibration datasets including Int Cal04, Marine04, and SHCal04 have been presented for ratification at the 18th International Radiocarbon Conference and are recommended for general use until further notice (Reimer et al., 2004). For marine samples such as shells, corals, fish etc. Since this dataset represents the "global" ocean, no marine reservoir correction should be made to the sample radiocarbon age prior to calibration, however a regional difference ΔR should be input as discussed in Section 2D.
Post-AD 1950 samples cannot be calibrated with CALIB.For the remaining period 12,400-26,000 cal yr BP, the curve is derived from independently dated marine samples such as foraminifera and corals.A new internationally-ratified calibration curve (Int Cal09) covering the whole radiocarbon timescale (~50,000 cal yr) is being prepared by the Int Cal Working Group.The program can be cited by the published description of a previous revision (Stuiver and Reimer, 1993) or the on-line version (Stuiver et al., 2005).References to the calibration dataset used should be cited as found in the program output. A calibration dataset is necessary to convert conventional radiocarbon ages into calibrated years (cal yr).Compared to conventional radiocarbon techniques such as Libby's solid carbon counting, the gas counting method popular in the mid-1950s, or liquid scintillation (LS) counting, AMS permitted the dating of much smaller sized samples with even greater precision.