Can carbon dating
Unfortunately, we aren't able to reliably date artifacts beyond several thousand years.Scientists have tried to extend confidence in the carbon dating method further back in time by calibrating the method using tree ring dating.Unfortunately, tree ring dating is itself not entirely reliable, especially the "long chronology" employed to calibrate the carbon dating method.The result is that carbon dating is accurate for only a few thousand years. This fact is born out in how carbon dating results are used by scientists in the scientific literature.But researchers have known at least since 1969 that the carbon-14 level has not been constant, so that the radiocarbon clock needs to be "calibrated." As a result, various schemes are used to correct and calibrate radiocarbon dates, including: In each case, radiocarbon dates, determined by well-established procedures and calculations, are compared directly with dates determined by the above methods, thus permitting the radiocarbon dates to be accurately calibrated with distinct and independent dating techniques.
For instance, even in the 1950s, when Willard Libby first developed the process, it was recognized that the scheme assumes that the level of carbon-14 in the atmosphere is constant.
Compare, for example, the uncorrected line (blue dotted line) with the calibration curve (red curve).
In other words, those hoping that uncertainties in radiocarbon dating, say in the assumption of constancy of atmospheric carbon-14 levels, will mean that specimens are really much younger than the measured dates, are in for a big disappointment -- it is now clear that specimens are actually somewhat older than the raw, uncalibrated reckonings.
In order for carbon dating to be accurate, we must know what the ratio of carbon-12 to carbon-14 was in the environment in which our specimen lived during its lifetime.
during the industrial revolution more carbon-12 was being produced offsetting the ratio a bit).