Radiocarbon dating ams
Cave deposits and varves have the potential to include old soil carbon, and there are as-yet unresolved issues with fluctuating amounts of C14 in ocean corals.
Beginning in the 1990s, a coalition of researchers led by Paula J.
Reimer and colleagues point out that Int Cal13 is just the latest in calibration sets, and further refinements are to be expected.
Reimer of the CHRONO Centre for Climate, the Environment and Chronology, at Queen's University Belfast, began building an extensive dataset and calibration tool that they first called CALIB.
Since that time, CALIB, now renamed Int Cal, has been refined several times--as of this writing (January 2017), the program is now called Int Cal13.
Although we don't have any 50,000-year-old trees, we do have overlapping tree ring sets back to 12,594 years.
So, in other words, we have a pretty solid way to calibrate raw radiocarbon dates for the most recent 12,594 years of our planet's past.