Geology has long been accustomed to utilizing classical chemical and physical methods in the solution of geologic problems. In recent years still another method having its origin in nuclear science has become available--the use of isotopic abundances and distributions in earth materials. In many cases a knowledge of isotopic compositions of earth materials permits deduction of the histories of these materials and delineation of the various processes to which they have been subjected in the past. Examples of the utility of isotope studies in geology include the use of carbon isotopes in revealing the mechanism by which marine carbonates are formed, the use of magnesium isotopes in investigating dolomitization, the utilization of carbon and sulphur isotopes in relating crud oils of common origin, and the application of carbon isotopes to study of petroleum genesis, diagenesis, and migration. The use of isotope studies as a geologic tool is still relatively new, but holds much promise as an important interpretive method of the future.

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