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.Int Cal combines and reinforces data from tree-rings, ice-cores, tephra, corals, and speleothems to come up with a significantly improved calibration set for c14 dates between 12,000 and 50,000 years ago.Other organic data sets examined have included varves (layers in sedimentary rock which were laid down annually and contain organic materials, deep ocean corals, speleothems (cave deposits), and volcanic tephras; but there are problems with each of these methods.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.In Nyerup's time, archaeologists could date the past only by using recorded histories, which in Europe were based mainly on the Egyptian calendar.
For example, in Int Cal09's calibration, they discovered evidence that during the Younger Dryas (12,550-12,900 cal BP), there was a shutdown or at least a steep reduction of the North Atlantic Deep Water formation, which was surely a reflection of climate change; they had to throw out data for that period from the North Atlantic and use a different dataset.
We should see some interesting results in the very near future.
Welcome to the K12 section of the Radiocarbon WEBinfo site.
The half-life of an isotope like C14 is the time it takes for half of it to decay away: in C14, every 5,730 years, half of it is gone.
So, if you measure the amount of C14 in a dead organism, you can figure out how long ago it stopped exchanging carbon with its atmosphere.