WHAT IS RADIOCARBON DATING AND IS IT A RELIABLE METHOD OF DATING ARCHAEOLOGICAL SITES? (cont)
By Sean Hancock
C14 Levels In Our Atmosphere
Libby's principlel of simultaneity, presumes that the levels of C14 in any particular geographical area has been constant and regular throughout the geological record. This presumption was integral to the validity of radiocarbon dating during the early years of its development. Indeed, you have to know how much C14 was present in an organism at the time of its death to be able to measure, reliably, how much of it has disintegrated. This assumption, as Renfrew points out, is not correct:
"It is now known, however, that the proportion of radiocarbon to ordinary C12 has not remained constant through time, and that before about 1000B.C. the deviations are so great as to make radiocarbon dates significantly in error." 
Advances in Dendrochronological research (the study of tree rings), shows conclusively that the amount of C14 in our atmosphere over the past 8000 thousand years has fluctuated significantly . Libby was starting with a false constant. His research was based on erroneous foundations.
The bristle cone pine, a tree that grows in southwestern regions of the USA, lives for thousands of years. Some, that are still alive today, began their life four thousand years ago. Furthermore, dead bristle cone logs that have been collected from the ground in the areas they grow, extend the tree ring record back by a further four thousand years. The California sequoia and the European oak are other trees that are useful as they also live for thousands of years .
As everyone knows, for every year of growth trees produce annual rings. These rings can be counted giving the age of the tree in question. It made sense then that the level of residual C14 in a tree ring that was say 6000 years old could be predicted as the level of C14 in our atmosphere was the same then as it is today. Wrong.
Tree ring analysis has shown, for example, that that the level of C14 in our atmosphere 6000 years ago was much higher than today. Consequently, samples dated from that age were "scientifically proven" to have been much younger than they actually were  - a contradiction in terms. Thanks to the work of Hans Suess graphs for correcting C14 values to compensate for the geophysical fluctuations of our atmosphere have been devised . However, this has heavily reduced the authority of C14 dates for samples that are older than 8000 years. We simply have no information on the level of radiocarbon in our atmosphere before this date.