I have no idea, but I learned more in the last five minutes while looking it up, than I have learned in the last month. Thanks for a great question.

Actually, the question should be how do you determine the half-life for potassium-40. (Potassium-40 is the radioactive isotope that is involved here. It turns into either Calcium-40 or Argon-40 as it decays.) To put it simply, the way that we determine the half-life or any radioactive isotope is to take a sample of that isotope and isolate it for a period of time. After this time, you analyze the sample to see how much of the original you have and how much of the decay products. We can then take these concentrations and the amount of time that we waited, plug them into a relatively simple equation, and determine the length of the half-life. The longer the half-life of the isotope in question, the longer we would have to wait before doing the analysis. This is the process in a nutshell. The specifics of just how to isolate the original isotope and how we measure the amounts that we start with and what we finish with will vary depending on the isotopes involve. Both the original and the decay products would have to be considered in deciding which methods to use. ********** "Max-Power: Thanks Glenn. I heard that they only examined the isotope for 3 days and then extrapolated the half-life to be somewhere like 1 million years. How can you possibly determine that kind of time in three days only?" You don't have to watch this process for a long time. You just need to be able to make some very, very precise measurements of the concentrations of the isotopes. The rate of decay for any isotope is constant. So, with the precise measurements we can extrapolate the half-life. The more precise the measurements, the better the calculation of the half-life.

They took the square root of evil, which is money and multiplied it by the radius of chocolate pi, subtracted formula 49 from the official date on the death certificate and that's how they came up with it.