Some of the atoms eventually change from one element to another by a process called radioactive decay.If there are a lot of atoms of the original element, called the parent element, the atoms decay to another element, called the daughter element, at a predictable rate.
Many people have been led to be skeptical of dating without knowing much about it. In spite of this, differences still occur within the church.
For example, most people don't realize that carbon dating is only rarely used on rocks. A disagreement over the age of the Earth is relatively minor in the whole scope of Christianity; it is more important to agree on the Rock of Ages than on the age of rocks.
The passage of time can be charted by the reduction in the number of parent atoms, and the increase in the number of daughter atoms.
Radiometric dating can be compared to an hourglass.
But because God has also called us to wisdom, this issue is worthy of study.