Radiometric Dating

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Radiometric Dating

• Most rocks have small amounts of radioactive
  materials inside of them
• Radioactive isotopes degrade at a constant rate
• Scientists can use the amount of radioactive
  decay that has occurred in a rock sample to
  estimate the age of the rock
• The original radioactive isotope is called the
  parent isotope. The isotope that it degrades into
  is called the daughter isotope. Scientists can
  measure the amount of daughter and parent
  isotopes in a sample and figure out its age.
• This only works on igneous and metamorphic rocks

MM Radioactive Decay Lab
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Half life

• The half life of a radioactive isotope is the
  amount of time it takes half the mass of the
  isotope to degrade into the daughter isotope

Four half-lives
One half-life
Three half-lives
Two half-lives
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Geologic time scale

• Paleontologists have been able to divide Earths
  history into time units based on the life-forms
  that lived only during certain periods.
• The division of Earths history makes up the
  geologic time scale.
• Four major subdivisions of geologic time are
  used eons, eras, periods, and epochs.

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• The longest subdivisionseonsare based upon the
  abundance of certain fossils.

• Next to eons, the longest subdivisions are the
  eras, which are marked by major, striking, and
  worldwide changes in the types of fossils
  present.
• Periods are units of geologic time characterized
  by the types of life existing worldwide at the
  time.
• Periods can be divided into smaller units of time
  called epochs

• Eras are subdivided into periods.

• Epochs are also characterized by differences in
  life-forms, but some of these differences can
  vary from continent to continent.

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Pg. 259 Fig. 12