What Are Isotopes and What Can Be Learned From Them

Fig. 2: The hydrological cycle - a schematic representation of the movement of water both above and below the earth's surface. The figure indicates approximate oxygen-18 values [expressed in the delta notation in parts per thousand (⁰/₀₀) deviation from the standard mean ocean water]. The oxygen-18 values change through environmental processes and can be used to trace the pathway and history of water.