Dating from the Adams and Eves Threads

That sounds a little crude.In fact, radioactive decay has been extensively observed and investigated, and has been should to alway be an exponential decay. That is, the rate of decay is proportional to the amount of the material present. The decay is quite accurately describably with an exponential probability distribution. This makes it possible to make quite accurate predictions, albeit probabilistic predictions.When a new dating method is devised, that method is independently tested by comparing dates measured with the new method with dates obtained by other known reliable dating methods.

Thanks, JonF. That's good information.

Radiation began when those atoms came into existence. The dating of rocks depends on radioactive decay that leaves byproducts behind in the rock. Then a measurement of the ratio of the undecayed atoms still in the rock and the amount of byproduct gives you how much decay there has been since the rock solidified. Using that, together with the known decay rate and the equations of decay, you can compute the time of solidification.

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Impeach Bush

Yes, Argon is a byproduct of Potassium 40 decay. You determine byproducts by observing the decay in a lab. You can measure the decay rate in the lab. Admittedly, that is over a much shorter period of time. You don't need a very accurate to determine that the method could be used for dating. If your decay rate is inaccurate, the dating will be inaccurate. This would give you a clock that can determine dates with high precision, but with a possible systematic error due to an inaccurate decay rate.Once you start using it for dating rocks, you can cross-check with dates determined by other methods of known accuracy. This is considered to be calibration of the measuring method. The calibration eliminates the systematic error (from inaccurate decay rate), and thus allows you to compute a more accurate decay rate. This field calibration is an important aspect of radiometric dating methods. Here is a web page with details on the dating method.

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Impeach Bush

One is analyzing atoms, the other is using a clock and measuring masses.

Hmm, perhaps not.I notice in Message 159, you wrote: No, it doesn't have to be 100% potassium. If it were, the potassium would likely oxidize pretty quickly, and that "rock" wouldn't last long. Other elements in the rock would not affect the ratio of potassium 40 to argon 40.What you need is a stable rock, containing some measurable amount of a chemically stable potassium compound. You need the rock to be such that argon cannot escape from the rock. What you measure, is the amount of potassium 40 still present in the rock, and the amount of argon 40. It is the ratio of potassium 40 to argon 40 that indicates how much of the potassium has decayed.For example, if there are about equal amounts of potassium 40 and argon 40, then half of the original potassium 40 has decayed. Hence the age of the rock is about the half-life of potassium 40 (1.3 billion years).The assumption being made is that the argon 40 all comes from potassium 40 decay. Since argon 40 is a gas, it is unlikely that any significant amount would be trapped in the rock at the time the rock solidified. The method is applied to igneous rock (rock that solidified from a lava flow, for example), and gives the age of the rock since the time it solidified.It doesn't matter what else is in the rock, provided that there are no other sources of argon 40, and no ways that some of the argon 40 could have escaped.

Okay, that's much clearer (and correct).