Radiometric dating answers com
However it is less useful for dating metal or other inorganic objects.
Most rocks contain uranium, allowing uranium-lead and similar methods to date them.
This depends on the decay of uranium-237 and uranium-238 to isotopes of lead.
Due to the long half-life of uranium it is not suitable for short time periods, such as most archaeological purposes, but it can date the oldest rocks on earth.
This method for rock dating is based on the decay of potassium-40 into argon: until the rock solidifies, argon can escape, so it can in theory date the formation of rock.
One problem is that potassium is also highly mobile and may move into older rocks.
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.
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.
Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness.
Note that although carbon-14 dating receives a lot of attention, since it can give information about the relatively recent past, it is rarely used in geology (and almost never used to date fossils).
Carbon-14 dating has an interesting limitation in that the ratio of regular carbon to carbon-14 in the air is not constant and therefore any date must be calibrated using dendrochronology.
Another limitation is that carbon-14 can only tell you when something was last alive, not when it was used.