Radiocarbon Dating Calibration

I've been intending to clear this off my "to blog on" pile for a few weeks. The Feb. 23 issue of Nature had a review article concerning the dates for the dispersial of modern humans into Eurasia. The substance of the article was this:

Radiocarbon dating has been fundamental to the study of human cultural and biological development over the past 50,000 yr. Two recent developments in the methodology of radiocarbon dating show that the speed of colonization of Europe by modern human populations was more rapid than previously believed, and that their period of coexistence with the preceding Neanderthal was shorter.

What caught my attention was the developments in radiocarbon dating. First are new methods to help filter out contaminants. The second concerns fluctuations in ancient atmospheric concentrations of [14]C and how these variations can be corrected for:

Continue Reading

The second breakthrough has emerged from recent research into the fluctuation patterns of the original [14]C content of the Earth's atmosphere over the past 50,000 yr. The most significant and internally consistent results have come from the dating of a series of 280 stratified radiocarbon samples recovered from a long sequence of deep-sea sediments in the Cariaco Basin near Venezuela, dated in 'calendrical' terms by reference to closely matching patterns of oxygen isotope ([18]O/[16]O) fluctuations in the independently dated Greenland Ice Sheet Project 2 (GISP2) ice-core records from central Greenland; from a similar sequence of datings from deep-sea sediments adjacent to the Iberian coast; from a series of 152 paired radiocarbon and high-precision uranium/thorium (U/Th) measurements on a number of fossil coral formations from the tropical Atlantic and Pacific; and from a sequence of similar, combined [14]C and U/Th dating of a long cave stalagmite formation from the island of Socotra off the Arabian coast. The results of these different measurements have recently been compared to give a "best-estimation" comparison between measured radiocarbon ages and 'absolute' calendar ages over the past 50,000 yr, in the recently published NotCal04 calibration study presented at the 2003 radiocarbon calibration conference in Wellington, New Zealand

Here is the accompanying figure showing calibrations in reference to the theoretical straight line.



From the figure you can see that we're talking about a difference of about 5-6 kyr at the most. This may be an important correction for certain studies, but it's not as big of a difference as some people imply when casting doubt on radiocarbon methods, such as claims that we don't know how much [14]C was in the atmosphere in ancient times so the observed ratios are meaningless.

(It's beyond the scope of this article, but under 10,000 yr is calibrated using such methods as dendrochronology--ie. tree rings. Also note that radiocarbon dating is not used on material older than about 50 kyr.)

Question for Western Geologist or Capt. Obsidian (or any other geologist): how is radiocarbon dating relevant to stalagmite formation? I know caves can be formed from carbonic acid, but is the carbonic acid really an accurate representative of contemporary atmospheric CO2?