Wikipedia ar ar dating
But not always -- contamination of both types is common.
To falsify K-Ar dating, as the claim is attempting to do, one must not only show that the predictions of K-Ar measurements lead to incorrect years, but that both assumptions (1) and (2) hold.
I can think of several possibilities in response to this question: 2 & 3 seem easily falsifiable - anyone else could simply repeat the procedure and see if their results were the same.
I haven't heard of this being done, however if you have some evidence to this effect please share it. I have very little knowledge in the field of radioactive dating, and I'm not even sure if 1 is a true statement.
Firstly: please try not to bring creation/evolution into this.
I will award the correct answer to a response which provides links to evidence and sound explanations.
Drawing inferences from radiometric dating requires at least two basic assumptions: Igneous rock often forms under conditions that favor (1).
Motivation for the question to follow: Some of the common mistakes we make in evaluating claims are resisting contrary evidence, looking for confirming evidence, and preferring available evidence.
To counteract these tendencies, we need to take deliberate steps to examine critically even our most cherished claims, search for disconfirming evidence as well as confirming, and look beyond evidence that is merely the most striking or memorable.
But basically, it's like seeing a TV image in a noisy signal. These (flawed) studies cite examples of "anomalous" ages from specific lava floes: Their claims: "Volcanic rocks produced by the lava flows which occured in Hawaii in the years 1800-1801 were dated by the potassium-argon method.
Each pixel is somewhat unreliable, but when you piece together the whole picture, the predictions of the hypothesis "that's Mr. Excess argon produced apparent ages ranging from 160 million to 2.96 billion years." (Kofahl and Segraves, 1975, p.200) These authors cite a study by Funkhouser and Naughton (1968) on xenolithic inclusions in the 1801 flow from Hualalei Volcano on the Island of Hawaii.
@Oddthinking: Dismissing claims of anomalous data is a No True Scotsman if it is done in a cavalier fashion.