Absolute Dating - Radioisotopes (fill-in)

Using the sequencing of rock units we can assign relative dates to geologic formations. To assign an absolute date (a specific number of years from the present), we use radioactive decay.

  1. Some _______________ of elements are unstable and spontaneously break apart. This process is called radioactive __________________ and the isotopes are termed __________________.
  2. As the unstable parent isotope decays, __________________ products form. These daughter elements result from the parent __________________ emitting an alpha particle, emitting a beta particle, or capturing an electron.
  3. Any of these transactions cause a new __________________ to be formed. There may be several steps in the __________________ process until a stable element is created. The sequence of ____________________________________ products is well defined, as are the decay rates.
  4. Parent elements are incorporated into minerals crystallizing in cooling __________________ . Daughter products produced by radioactive decay of the parent isotopes are __________________ in the mineral.
  5. By measuring the __________________ of parent to daughter elements in that mineral we can determine how a long ago the mineral __________________ .
  6. Number of Half-lives Parent Isotope Remaining (%) Daughter Isotope (%)
    0 100 0
    1 50

    12.5 87.5
    4 6.25
    The usual way to describe the radioactive __________________ __________________ is half-life. This is the time it takes for one half (½) of the __________________ isotope to decay into the __________________ product. After one half-life, 1.0 g of a parent has decayed into 0.5 g of parent and 0.5 g of daughter product. After two half-lives, there is 0.25 g of parent and 0.75 g of daughter product.
  7. Knowing the half-life of a parent isotope and determining the __________________ of parent isotope to daughter product in a mineral sample allows us calculate the time since the mineral __________________ .
  8. The table below lists five parent / daughter __________________ __________________ that are useful for dating minerals. Potassium-Argon is often used due to the sensitivity of laboratory techniques for these elements and the fact that potassium is found in many common minerals such as feldspars and micas.
    Radioactive Parent Half-life (in billion years) Stable Daughter Product
    Uranium 238 4.5 Lead 206
    Uranium 235 0.71 Lead 207
    Thorium 232 14.1 Lead 208
    Rubidium 87 47.0 Strontium 87
    Potassium 40 1.3 Argon 40