Talkorigins radiometric dating
Some radiometric dating methods depend upon knowing the initial amount of the isotope subject to decay.For example, the C14 concentration in the atmosphere depends upon cosmic ray intensity.To take this into account, a calibration curve is developed using other dating methods to establish the C14 levels over time.Other methods do not require knowing the initial quantities.
For example, potassium decays into two different isotopes of argon having different half-lives.
Argon/argon dating works using only the ratio of the concentration of the argon isotopes. For the purposes of this debate, "accurate" means that 95% of the dating errors are within 10% of the measured date, within the time span for which the isotope pair is utilized.
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