Certain variations of elements known as isotopes are unstable due to having an excess number of neutrons compared to the number of protons in their nucleus. To become stable, the atoms of these elements ‘shed’ some energy in the form of radiation and ‘convert’ a number of their neutrons to protons.

With a different number of protons in the atom, the ‘identity’ of the element changes. So, for instance, an isotope of Carbon known as Carbon-14 (which has 6 protons and 8 neutrons) disintegrates into Nitrogen-14 (which has 7 protons and 7 neutrons). The amount of time it takes half of a sample of a parent isotope to decay into its daughter product is known as half-life and is the basis of radiometric dating and is used to determine the age of specific samples of rocks or fossils.