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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
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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 it’s age. • This only works on igneous and metamorphic rocks Radiometric Dating M&M Radioactive Decay Lab
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 Two half-lives Three half-lives
Geologic time scale • Paleontologists have been able to divide Earth’s history into time units based on the life-forms that lived only during certain periods. • The division of Earth’s history makes up the geologic time scale. • Four major subdivisions of geologic time are used— eons, eras, periods, and epochs.
The longest subdivisions—eons—are 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. • Periodsare 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.
