Carbon 14 dating fossils
A final assumption is that the various rates of flow of carbon-14 among the respective geophysical reservoirs must be constant, and the residence time of carbon-14 in the various reservoirs must be short relative to its half-life. (Riverside, CA: La Sierra University Press, 1997), 183. Carbon-14 dating models and experimental implications. Origins 24(2, 1997):50-64  The deep ocean waters are estimated to take about 1000 years to circulate back to the surface: Aitken, MJ. If these three conditions are met, the initial concentration of C in the sample can be estimated. While the small variations in isotope decay that have been reported may not invalidate all isotopic dating, they raise questions about the assumption of completely uniform decay rates.A second assumption is that the sample being dated has not experienced any loss or contamination of C over its history.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.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.
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 widely used in dating fossils or archaeological samples containing organic material such as wood, charcoal, bone, shells, etc.It is not used to date rocks or other inorganic material.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.