Rubidium strontium dating example
In old rocks, there will be less potassium present than was required to form the mineral, because some of it has been transmuted to argon.
The decrease in the amount of potassium required to form the original mineral has consistently confirmed the age as determined by the amount of argon formed.
Carbon-14 dating: See Carbon 14 Dating in this web site.
Rubidium-Strontium dating: The nuclide rubidium-87 decays, with a half life of 48.8 billion years, to strontium-87.
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.
Therefore the relative amounts of rubidium-87 and strontium-87 can be determined by expressing their ratios to strontium-86: Rb-87/Sr-86 and Sr87/Sr-86 We measure the amounts of rubidium-87 and strontium-87 as ratios to an unchanging content of strontium-86.
Because of radioactivity, the fraction of rubidium-87 decreases from an initial value of 100% at the time of formation of the mineral, and approaches zero with increasing number of half lives.
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.
An atom with the same number of protons in the nucleus but a different number of neutrons is called an isotope.