Scientists can find the absolute age of a rock by using

a uranium 235 dating

b carbon 14 dating

c carbon 12 dating

d relative dating

Carbon-14 is normally used to date living organisms (all living things we know today contain mostly carbon). It can be used for samples up to about 60000 years old. Carbon-12 is the non-radioactive form that we encounter daily. Relative dating determines dates relative to each other, such as ordering of period or events.

Uranium 235 dating can determine date samples a million years old and up, so is more suited for rocks.