Radiological dating methods
This does not mean that all rock samples are unreliable, but it is possible to account for a process which throws off the data for metamorphic rocks.
For example, with Uranium-lead dating with the crystallization of magma, this remains a closed system until the uranium decays.
The energy locked in the nucleus is enormous, but cannot be released easily.
The phenomenon we know as heat is simply the jiggling around of atoms and their components, so in principle a high enough temperature could cause the components of the core to break out.
In the case of carbon dating, it is not the initial quantity that is important, but the initial ratio of C, but the same principle otherwise applies.
Recognizing this problem, scientists try to focus on rocks that do not contain the decay product originally.
It is more accurate for shorter time periods (e.g., hundreds of years) during which control variables are less likely to change.
As it decays, it disrupts the crystal and allows the lead atom to move.