Some minerals in rocks and organic matter (e.g., wood, bones, and shells) can contain radioactive isotopes. The abundances of parent and daughter isotopes in a sample can be measured and used to determine their age. This method is known as radiometric dating.

What are radioactive isotopes and how are they used to date rocks?

Radioactive dating is a method of dating rocks and minerals using radioactive isotopes. This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Over 300 naturally-occurring isotopes are known.

How are radioactive isotopes used to determine the age of rock?

Radioactive isotopes are unstable and will decay. The isotopes will decay into a stable isotope over time. Scientists can tell how old the rock was from looking at the radioactive isotopes half-life, which tells them how long it would take for there to be half the radioactive isotope and half the stable isotope.