Stable isotope geochemistry

Article By:

Kyser, Kurt Department of Geological Sciences, Queen's University, Kingston, Ontario, Canada.

Last reviewed:2007

DOI:https://doi.org/10.1036/1097-8542.YB070500

The origin and fate of elements and their compounds (such as in fluids, metals, nutrients, organics, gases, and pollutants) in planetary, Earth, and environmental sciences is most effectively traced using stable-isotope geochemistry. Isotopes of an element are atoms having the same number of protons but different numbers of neutrons. All but 35 elements have more than one stable isotope that can be used to trace the element through various natural systems. In contrast to unstable (radioactive) isotopes or isotopes produced from the decay of another element (radiogenic), stable-isotope geochemistry uses isotopes whose abundances do not change with time. For example, oxygen has three stable isotopes, each having eight protons, but 99.763% of oxygen atoms have eight neutrons (¹⁶O, where 16 is the atomic number and refers to the sum of protons plus neutrons), while 0.0375% have 9 (¹⁷O) and 0.1995% have 10 (¹⁸O) [see table]. The three isotopes of oxygen share the same general chemical properties, but differ in mass and therefore form bonds with slightly different energies, which results in differential partitioning of the light and heavy isotopes of oxygen among various compounds.

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