How do scientists use radioisotopes to determine absolute dates for rocks?
Radioisotopes are used by scientists to date rocks in a method called radiometric dating. The isotopes of an element are the atoms that have the same number of protons and electrons but different numbers of neutrons. When atoms of a radioactive isotope are included in the formation of a crystal, that crystal becomes the parent isotope. As the isotopes begin to decay, they become a daughter isotope. The convenient property of this phenomenon is that a certain parent isotope will ALWAYS decay to a certain daughter isotope. The rate of decay from parent to daughter isotope is called the half-life (time for half of the parent to become the daughter). Being familiar with and using isotopes such as Uranium-238, Uranium-235, and Carbon-14, scientists are able to calculate the age of a rock, fossil, etc. using the known half-life for each parent isotope.
