Potassium argon dating animation
Indeed, if Dalrymple’s data is representative, 3 times out of 26 the K-Ar method will give a too young date (though by only an extremely trivial amount for a rock that is really millions of years old). The one case that would have produced a significant error, the Hualalai flow in Hawaii, was expected (see the previous essay). Naughton, 1968, 'Radiogenic Helium and Argon in Ultramafic Inclusions from Hawaii,' J.
Of the 26 lava flows that were sampled and analyzed, 18 of them gave expected results. Eight rocks yielded unrealistic dates, which were either too old because of the presence of excess 40Ar (5 of them) or too young (negative ages) because of the presence of excess 36Ar (3 of them).
Even that significant error is only 1.19 million years (and not the 1.60 million years that Snelling claimed).
If the identical rock had been formed 50 million years ago, the K-Ar would give a "false" age of a little over 51 million years.
The rock sample to be dated must be chosen very carefully.
Any alteration or fracturing means that the potassium or the argon or both have been disturbed.
In addition, excess argon is even less of a problem with Ar-Ar dating, where excess argon can often be distinguished from radiogenic argon and its effects eliminated (Mc Dougall and Harrison, 1999, p. , Snelling failed to properly quote the 'apparent K-Ar dates' from Table 2 in Dalrymple (1969, p. That is, Snelling mistakenly listed the concentrations of 40Ar (in 10 to the -12 moles/gram) for the Hualalai, Mt. Lassen, and Sunset Crater samples as their apparent K-Ar dates!!