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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.Another limitation is that carbon-14 can only tell you when something was last alive, not when it was used.
A proper radiometric date should read years before present (with 1950 being present) ± range/2 at x standard deviations (Xσ)', but is often reported as a single year or a year range, like 1260–1390 CE (the date for the Shroud of Turin).
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.
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.