While I was  on the web researching and verifying some of the facts used here (e.g. details of 14C formation and decay) I came across a link to a criticism of radiocarbon dating at the Answers in Genesis website (answersingenesis,org).

The criticism is that Willard Libby (the scientist who developed the 14C dating method) estimated that starting with no 14C in the atmosphere (or in living organisms) the process of creating14C (and its subsequent decay back to nitrogen) would take 20,00 to 30,000 years before the amount of 14C would stabilize at current levels (creation of new 14C would match the decay).  I have not come across this criticism before, but I believe that it is substantially correct.  That is:  it would take 20,000 to 30,000 years for 14C levels to build up (from scratch) to a stable level.  They, the “Creationists,” also claim that Libby and the rest of the “Darwinists” then ignored this calculation, claiming that 14C levels a stable and therefore 14C dating is an accurate dating tool.  It is true that when14C dating was first used that that was the assumption that there was no variation.  “At first,” I’ll come back to this point later.

The real problem is where the Creationists went with all this.  Answers in Genesis claims that14C levels vary and that Darwinists know this and ignore it because it falsifies all their (“our” since I am a “Darwinist”) dates.  Then they imply that since14C levels vary, the earth hasn’t existed  long enough for the levels to stabilize.  That is, God created the world less than 20,000 or 30,000 years ago and 14C levels have not reached stability and therefore radiocarbon dating is a conspiracy by “Darwinists” to hide the truth (perhaps I should say:  Truth).

Anyway they ignore some other factors.  (This is typical of so many Creationists arguments).  14C levels do vary a little over time, sometimes more, sometimes less.  The levels are stable around a point.  If the levels were still approaching the stabilization level because we are still so close to the “zero” point at creation then, as per Libby’s calculation, the14C level would be steadily rising toward that point, not “varying.”  The implication of the Creationist use of “varying” is that the levels are all over the place.  It has been more than 30,000 years since there was zero 14C in the atmosphere (more like 30,000,000,000 years).  the C14 levels have long since stabilized and vary a little over time because of the varying influx of the cosmic rays that create 14C from nitrogen.

Contrary to the Creationists implication the scientists are hiding this, scientists are well aware of this variation.  We didn’t ignore (told you I would return to this point) and it is in the background of 14C dating and discussions about the “real” date derived by 14C dating.  Using techniques like dendrochronology (tree-ring dating where we can use 14C dating to date a specific ring for which we know the exact year, independent of a 14C radiocarbon date) we can compare the14C date to the actual year and determine the amount of error for each year due to variation in cosmic ray radiation. There are computer programs for this.

Dendrochronology dating can extend back in time more than 10,000 years.  Using it a some other methods, it is possible to reconstruct how 14C levels has varied over the past 40,000 or 50,000 years (the current limit for most14C dating methods) and know how the derived radiocarbon dates need to be corrected to be more accurate and be real “corrected” years.  Which is why 14C dates are in14C years, so that as the correction factors become more accurate, inaccurate dates based on old, obsolete data do not become embedded in the scientific literature and cause problems. For example, in a report on some site or artifact, the report will state that it is “so many radiocarbon years old,” rather the say 9600BP years (before present, or 7,650BC, “present” is define as 1950AD).  As newer 14C correction programs appear, you can easily make your own, more accurate correction because the actual 14C date is in the literature, rather than some correct date whose corrected date may no longer be right and you have no idea what the correction was.  I have a program that I used to use back when I was working as an archaeologist that has been superseded by newer, more accurate programs.  You can probably find them on the internet.  I mean, this program is so old it is on a 5 1/4 inch floppy disk.  The disc is floppy, it bends.  I haven’t used it in 25 or 30 years and wouldn’t use to calibrate a14C date if I needed to.  Besides I doubt that I have a computer that  could run it, It is so old.