Radiometric dating answers com
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.
The key is to measure an isotope that has had time to decay a measurable amount, but not so much as to only leave a trace remaining.
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.
The time that it takes for half of a sample to decay is known as the half life of the isotope.
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.
One problem is that potassium is also highly mobile and may move into older rocks.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.The half-life of carbon-14 is approximately 5,730 years. Since the quantity represents 13% (or 13/100ths) of , it follows that This is based on the decay of rubidium isotopes to strontium isotopes, and can be used to date rocks or to relate organisms to the rocks on which they formed.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.