Although the time at which any individual atom will decay cannot be forecast, the time in which any given percentage of a sample will decay can be calculated to varying degrees of accuracy.
The time that it takes for half of a sample to decay is known as the half life of the isotope.
Although, organic materials as old as 100,000 years potentially can be dated with AMS, dates older than 60,000 years are still rare.
Paleoanthropologists and archaeologists must always be aware of possible radiocarbon sample contamination that could result in inaccurate dates.
The uncertainties in the crucial K/K abundance ratio also need to be considered, because there is no agreement on it.
The value of 0.011672±0.000041% determined in 1975 is still adopted, but the value of 0.011668±0.000008% determined in 2013 has yet to be recognized.
Since there doesn't seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.
However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over 500 million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old.
We are told that these methods are accurate to a few percent, and that there are many different methods.Therefore, when all these factors are considered the total K decay half-life, the adopted value ultimately depends on deriving it by adjusting (that is, massaging) K-Ar and Ar-Ar ages to conform to U-Pb and Pb-Pb ages obtained from different minerals respectively in the same rocks. But many unprovable assumptions are also involved, not the least being that the radioisotope systems closed at the same time and subsequently remained closed. “Analysis of the Relative Decay Constants of Ar Method. How radiometric dating works in general Why methods in general are inaccurate Why K-Ar dating is inaccurate The branching ratio problem How Errors Can Account for the Observed Dates Why older dates would be found lower in the geologic column especially for K-Ar dating Do different methods agree with each other on the geologic column?Possible other sources of correlation Anomalies of radiometric dating Why a low anomaly percentage is meaningless The biostrategraphic limits issue Preponderance of K-Ar dating Excuses for anomalies Need for a double-blind test Possible changes in the decay rate Isochrons Atlantic sea floor dating Dating Meteorites Conclusion Gentry's radiohaloes in coalified wood Carbon 14 dating Tree ring chronologies Coral dating Varves Growth of coral reefs Evidence for catastrophe in the geologic column Rates of erosion Reliability of creationist sources Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium.There are important sources of systematic error in all Ar with γ-rays emitted is still not definitively agreed upon.