Argon in molten rock can just bubble out and escape.
K has a half-life of 1.248 billion years, which makes it eminently suitable for dating rocks.
The determinations since 1997 have converged with close agreement toward the total K decay half-life value of 1.2524±0.0064Byr.
But that determination in 2011 ignored the two liquid scintillation direct counting determinations in 20 which had agreed on a slightly lower total K decay half-life value of 1.248±0.003Byr.
Ar Analyses of Historic Lava Flows.” Nevertheless, this is no way changes the argument in question.
This could even be the case when the K-Ar and Ar-Ar analyses yield "dates" compatible with other radioisotopic "dating" systems and/or with fossil "dating" based on evolutionary assumptions.
Furthermore, there would be no way of knowing, because the Ar not from radioactive decay, except of course by external assumptions about the ages of the rocks.
The value of 0.1162 was used in 2011 in spite of the value of 0.1194±0.007 carefully determined in 2000, which confirmed the value of 0.1195±0.0014 determined in 1973.
The uncertainties in the crucial K/K abundance ratio also need to be considered, because there is no agreement on it.
The value of 0.011672±0.000041% determined in 1975 is still adopted, but the value of 0.011668±0.000008% determined in 2013 has yet to be recognized.