Under natural conditions, elements occur as mixtures of isotopes. Different isotopes of the same element react chemically in same way. Some isotopes are radioactive. Has a fixed half life . Dating geological strata and fossils.
Radioactive decay is at a fixed rate.
By comparing the ratio of radioactive and stable isotopes in a fossil with the ratio of isotopes in living organisms, one can estimate the age of a fossil. The ratio of 14 C to 12 C is frequently used to date fossils less than 50,000 years old. Radioactive tracers Chemicals labelled with radioactive isotopes are used to trace the steps of a biochemical reaction or to determine the location of a particular substance within an organism. Radioactive isotopes are useful as biochemical tracers because they chemically react like the stable isotopes and are easily detected at low concentrations. Isotopes of P, N and H were used to determine DNA structure.