Figure 1. Radiocarbon data are given in D notation, the per mil deviation in ¹⁴C/¹²C ratio from a standard (1895 wood). Positive D ¹⁴C values indicate the predominance of C derived from the atmosphere since the period of weapons testing which peaked in the mid-1960's. Negative values indicate that C has resided long enough for significant radioactive decay of ¹⁴C (which has a half-life of 5730 years). Analytical error on all samples is + or - 6 per mil.