Using the argon-argon dating technique, by which scientists measure the decay of an isotope called Argon-40 into Argon-39 in order to find the age of crystals, they came up with a rough approximation of the footprints' age: 19,000 years at the oldest, 10,000 or 12,000 years at the youngest.
I can't exactly follow the logic, but I'm asking here about the dating process itself. I do not think that Argon-40 decays into Argon-39 as the article states, at least not all by itself. Based on the atmospheric 40-Ar/36-Ar ratio and the 36-concentration, the 40-Ar concentration at the time of formation is calculated.
In the case of potassium-argon decay, this loss of a proton causes the atom to change from a reactive alkali metal to a non-reactive noble gas, which is an important characteristic.
Other corrections must be made to account for the proportion of throughout the biosphere (reservoir effects).The electrical current breaks the compound into its elements.(See sidebar on Davy in the calcium entry in Volume 1.) There are very few uses for potassium as a pure element.The periodic table is a chart that shows how chemical elements are related to one another.The alkali metals also include lithium, sodium, rubidium, cesium, and francium. Potassium is so active that it never occurs free in nature.Davy used a new method of isolating elements that he had invented, electrolysis.In electrolysis, an electric current is passed through a molten (melted) compound.And when I look at the Wikipedia article, the discussion is so technical and defensive that I can't actually picture what is going on. You are right: there is no decay of 40-Ar into 39-Ar. The difference between measured 40-Ar and 40-Ar at formation is used in the procedure.But then, different passages in the Wikipedia article contradict each other (first section: 39-K is converted into 39-Ar by neutron bombardment; but "age equation" section: 40-K is bombarded; I think it should be 39-Ar).The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.