[palmer]

if you take new charcoal and have it dated you will get a fairly ancient date because due to the burning of very old carbon deposits (many of which have been underground for over 300 million years) the concentrations of C-14 have dropped significantly.

My understanding is 1950 is the end of 14C dating because the atmospheric nuclear tests put too much 14C in the carbon cycle after that, not because there's too little from anthropogenic carbon. In any case the 13C/12C ratio has been rising since 1850 and I would believe that 14C has done the same.

[palmer]

Correction: 13C/12C decreasing because of anthropogenic sources and 14C should be doing the same.