Potassium half life dating
It has the same number of protons, otherwise it wouldn't be uranium.
The number of protons in the nucleus of an atom is called its atomic number.
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.
(Do not confuse with the highly radioactive isotope, strontium-90.) Strontium occurs naturally as a mixture of several nuclides, including the stable isotope strontium-86.
If three different strontium-containing minerals form at the same time in the same magma, each strontium containing mineral will have the same ratios of the different strontium nuclides, since all strontium nuclides behave the same chemically.
Strontium-86 is a stable element that does not undergo radioactive change.
In addition, it is not formed as the result of a radioactive decay process.
At the same time, the fraction of strontium-87 increases from zero and approaches 100% with increasing number of half-lives.
(Creationists claim that argon escape renders age determinations invalid.
However, any escaping argon gas would lead to a determined age younger, not older, than actual.
The creationist "argon escape" theory does not support their young earth model.) The argon age determination of the mineral can be confirmed by measuring the loss of potassium.
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.
(Note that this does not mean that the ratios are the same everywhere on earth.