Contamination from outside, or the loss of isotopes at any time from the rock's original formation, would change the result.
It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.
Measurements should be taken on samples from different parts of the rock body.
This helps to counter the effects of heating and squeezing, which a rock may experience in its long history.
Any argon present in a mineral containing potassium-40 must have been formed as the result of radioactive decay.
F, the fraction of K40 remaining, is equal to the amount of potassium-40 in the sample, divided by the sum of potassium-40 in the sample plus the calculated amount of potassium required to produce the amount of argon found. In spite of the fact that it is a gas, the argon is trapped in the mineral and can't escape.
Radiometric dating (often called radioactive dating) is a way to find out how old something is.
The decay may happen by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous nuclear fission, and electron capture.Therefore the amount of argon formed provides a direct measurement of the amount of potassium-40 present in the specimen when it was originally formed.Because argon is an inert gas, it is not possible that it might have been in the mineral when it was first formed from molten magma.Radioactive elements "decay" (that is, change into other elements) by "half lives." If a half life is equal to one year, then one half of the radioactive element will have decayed in the first year after the mineral was formed; one half of the remainder will decay in the next year (leaving one-fourth remaining), and so forth.The formula for the fraction remaining is one-half raised to the power given by the number of years divided by the half-life (in other words raised to a power equal to the number of half-lives).If we knew the fraction of a radioactive element still remaining in a mineral, it would be a simple matter to calculate its age by the formula To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed.Contrary to creationist claims, it is possible to make that determination, as the following will explain: By way of background, all atoms of a given element have the same number of protons in the nucleus; however, the number of neutrons in the nucleus can vary.The method works best if neither the parent nuclide nor the daughter product enters or leaves the material after its formation.Anything which changes the relative amounts of the two isotopes (original and daughter) must be noted, and avoided if possible.An atom with the same number of protons in the nucleus but a different number of neutrons is called an isotope.For example, uranium-238 is an isotope of uranium-235, because it has 3 more neutrons in the nucleus.