[music_code]

All of them are based on the observable decay rates and resultant ratios of parent/daughter isotopes. And, the fact that multiple dating methods agree with one another is an indication of their accuracy.

These methods are far from infallible and are based on three arbitrary assumptions: a constant rate of decay, an isolated system in which no parent or daughter element can be added or lost, and a known amount of the daughter element present initially.

Hope this clears up your confusion.

[Junior]

Decay rates are based on statistics -- over X number of years, Y number of atoms will decay into Z atoms of a daughter isotope. Since we are dealing with hundreds of trillions of atoms, the statistics will bear out. Faster decay rates in the past would definitely leave a mark on the landscape (at least two folks here have pointed out that, based on creationists assumptions, Adam and Eve would have been toast).

Lava flows (and other igneous formations) make great yard sticks for radiometric dating because heated rocks release the daughter isotopes whose ratio is used for dating. Hence, lava can be dated most accurately and rock formations above ancient lava flows would have to be younger, while those below would be older. Also, this is another reason that multiple tests are conducted on the same samples using different methods. Even if there was a skew in one parent-daughter ratio, that exact same skew would not be present in another parent-daughter ratio. If several methods converge on a specific date, odds are that's how old the rock is.

[Doctor Stochastic]

Actually, the datings from various means are remarkably consistent.

Christian Perspective on Dating