Potassium 40 dating accuracy
Two situations where we can do this involve Potassium-40 atoms and Carbon-14 atoms.All radioactive atoms decay to become a more stable kind of atom.Once the organism dies, this exchange stops and the Carbon-14 that decays is not replaced.By measuring the percentage of Carbon-14 left, and comparing it to the percentage of Carbon-14 in the atmosphere, we can date organic specimens up to 70000 years old.(see link) Scenario: I heard about a group of people (yes they happen to be creationists with an agenda, but this should be irrelevant to the question I am posing!) who obtained some samples of rocks from a lava flow from Mt Ngauruhoe in New Zealand.A small percentage of this Carbon is the radioactive form, Carbon-14.While an organism is alive this exchange of Carbon continues, and the percentage of Carbon-14 in its body is the same as the percentage of Carbon-14 in the atmosphere.
The number used to identify the isotope refers to the total number of particles in the nucleus of each atom.
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.
Once the rock cools and solidifies, Argon that is formed by radioactive decay is trapped inside.
As no Argon was present in the rock when it first solidified, all Argon in the rock is due to the radioactive decay of Potassium.
edit 1 above i said Statistically significant disparity in measured ages is inconsistent with the assumptions required to make radiometric dating predictions.