Radiometric dating answers com
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.
Most rocks contain uranium, allowing uranium-lead and similar methods to date them.
are very much older than the approximately 6,000 to 10,000 years reckoned by young earth creationists.