Isotopes: Tiny atoms tell stories eons old (GC-08)
Relative amounts or ratios of different isotopes of special chemical elements can tell ages and much more about geologic samples, even moon rocks. Certain elements are really chemical families whose members, or isotopes, share identical electronic structure, number of electrons and protons, and chemical behavior but differ in number of neutrons in the nucleus. Different isotopes of any element have different masses, varying in multiples of 6 X 10^-26 ounces. A mass spectrometer (seen above) is used to distinguish isotopes and record their ratios.

In the mass spectrometer, charged atoms are electronically "shot" down a tube under high vacuum and through a magnetic field. This field causes the atoms to change direction and bends lighter isotopes more than heavier ones. By varying the magnetic field, beams of different isotopes can be focused onto an electronic measuring device that records the relative amounts of the isotopes. In this way, geologists can "see" back into time.

Our Hoosier State Beneath Us: Geochemistry/Geophysics