Radioactive decay and dating
The corresponding half lives for each plotted point are marked on the line and identified.
It can be readily seen from the plots that when this procedure is followed with different amounts of Rb87 in different minerals, if the plotted half life points are connected, a straight line going through the origin is produced. The steeper the slope of the isochron, the more half lives it represents.
Potassium-Argon dating: The element potassium (symbol K) has three nuclides, K39, K40, and K41. K40 can decay in two different ways: it can break down into either calcium or argon.
The ratio of calcium formed to argon formed is fixed and known.
(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.
Rubidium-Strontium dating: The nuclide rubidium-87 decays, with a half life of 48.8 billion years, to strontium-87.
At this point the fraction of Rb87 = Sr87 = 0.500; at half life = 2.00, Rb87 = 25% and Sr87 = 75%, and so on. 131, Strahler, Science and Earth History: Points are taken from these curves and a plot of fraction Sr-87/Sr-86 (as ordinate) vs. It turns out to be a straight line with a slope of -1.00.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.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.