Argon radiometric dating
Some isotopes have half lives longer than the present age of the universe, but they are still subject to the same laws of quantum physics and will eventually decay, even if doing so at a time when all remaining atoms in the universe are separated by astronomical distances.
Various elements are used for dating different time periods; ones with relatively short half-lives like carbon-14 (or C) are useful for dating once-living objects (since they include atmospheric carbon from when they were alive) from about ten to fifty thousand years old. Longer-lived isotopes provide dating information for much older times.
To date older fossils, other methods are used, such as potassium-argon or argon-argon dating.
Radiometric dating — through processes similar to those outlined in the example problem above — frequently reveals that rocks, fossils, etc.
This is consistent with the assumption that each decay event is independent and its chance does not vary over time.
The solution is: where is the half-life of the element, is the time expired since the sample contained the initial number atoms of the nuclide, and is the remaining amount of the nuclide.
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