Strontium-87 is a stable element; it does not undergo further radioactive decay.(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.(Note that this does not mean that the ratios are the same everywhere on earth.
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.
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.
(Creationists claim that argon escape renders age determinations invalid.
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.
Styrian pumpkin seed oil, a specialty of southeastern Austria that can cost upward of for a handful of ounces, is another food that has been traced in a similar manner.