Atom used in radiocarbon dating
This ratio would have been different before the Flood. According to these authors, the total mobile (non-carbonate) carbon in the biosphere is about 40,000-45,000 gigatons. The global carbon cycle: a test of our knowledge of Earth as a system.
The earth’s sediments contain a vast amount of carbon-12 in the form of coal and oil.  Post WM, Peng TH, Emanuel WR, King AW, Dale VH, Deangelis DL. The amount of carbon in fossil fuels is estimated at 6,000 gigatons, and the amount of kerogens (organic) in sediments is about 15 million gigatons.
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.
Carbon-14 dating cannot be applied to materials that have no C dates are less than that figure.
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.
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.
Another assumption is that the amounts of carbon-14 present in the geophysical reservoirs must be constant.
Three additional assumptions are necessary in radiocarbon dating in order to estimate the initial concentration of C could be caused by changes in the intensity of the cosmic radiation or in the strength of the earth’s magnetic field.Why do ancient samples of coal, diamonds and other carbon-containing materials consistently contain  The first such curve was published by: Arnold, JR and WF Libby. High-precision (super 14C measurement of Irish oaks to show the natural 14C variations from AD 1840 to 5210 BC. Age determinations by radiocarbon content: Checks with samples of known age. Subsequent revisions have been made, e.g., Reimer, PJ et al. 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).