Dinosaurs became extinct 65 million years ago, and there is still much debate as to what caused the extinctions.

      In the 1940's Harold Urey set out to determine why the dinosaurs went extinct at the K/T boundary; he began isotopically analysing invertebrates with the intention of creating a paleotemperature scale (Barrick, 1998). He believed that there may have been a climatic shift at the K/T boundary that caused the extinction of the dinosaurs (Barrick, 1998).  Since then the field of isotope paleontology has expanded greatly, and in the past decade it has virtually exploded (Corfield and Norris, 1998).

     Applications of isotope geology go well beyond geochronology. Today, and in recent years more and more geologists; including paleontologists, paleobiologists, and paleoecologists are using isotopic methods to aid in the unraveling of the complex puzzles that we call our work.  A paleontologist may use strontium seawater analysis in an attempt to date a particular formation.  A paleoecologist may use the same strontium isotopic values to determine salinity values for a debunked ecosystem. A paleobiologist may use oxygen isotopes to aid in the determination of thermoregulatory controls in an extinct creature.

A mass spectrometer is necessary for isotope studies; they are used to separate atoms on the basis of atomic mass .