Radiometric dating example problems
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.
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.
It suffers from the problem that rubidium and strontium are very mobile and may easily enter rocks at a much later date to that of formation.
The half-life , specific to each nuclide, can be accurately measured on a pure sample, and is known to be independent of the chemical composition of the sample, temperature and pressure.To date older fossils, other methods are used, such as potassium-argon or argon-argon dating.Other forms of dating based on reactive minerals like rubidium or potassium can date older finds including fossils, but have the limitation that it is easy for ions to move into rocks post-formation so that care must be taken to consider geology and other factors.Most rocks contain uranium, allowing uranium-lead and similar methods to date them.Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness.
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The oldest rock so far dated is a zircon crystal that formed 4.4-billion-years ago, which was only 200 million years or so after the Earth itself formed.