3 assumptions of radiometric dating
Int Cal09 and Marine09 radiocarbon age calibration curves, 0-50,000 years cal BP.  This was the scroll “Testament of Qahat,” for which the radiocarbon date was about two centuries older than the date based on paleography. A detailed survey of the following dating methods in actual use: K-Ar, Ar-Ar, Fission track, Rb-Sr, U-Pb, Pb-Pb, Sm-Nd, Re-Os, Lu-Hf, La-Ce, etc.Violations in the atmosphere result from volcanic eruptions that occasionally add C.Also, there is a lag time for atmospheric mixing in the northern and southern hemispheres which results in somewhat different ages for the two hemispheres.In practice, there are sufficient variations in these conditions that it is necessary to correct a sample’s raw radiocarbon age by comparing it with the standard calibration curve.
It is sometimes thought possible to extend the dating range a few half-lives, so one occasionally sees dates as old as 70,000 years or more.
This can be done very accurately, although some samples may be difficult to work with.
Beyond this, the accuracy of the date depends on the reliability of the assumptions used in interpreting the measurements (see below).
The geophysical reservoirs include the atmosphere, the oceans, the biosphere, and the sediments.
Violations of this assumption occur in the ocean reservoir due to the time required for mixing of surface waters with the deep layers.
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It is known that such variations have occurred, but it is thought they can be corrected for by comparing a sample’s C level with the standard curve constructed using samples of known age.