12/7/16
Determining Absolute Age
OBJECTIVE: I WILL MODEL RATES OF RADIOACTIVE DECAY
THROUGH A GRAPHING ACTIVITY.
PAGE 45
Absolute Age
 absolute age- the exact numeric age of an object or
event
Radiometric Dating
 method of using radioactive decay to measure
absolute age
Radiometric Dating
 rocks contain unstable radioactive isotopes that emit particles
(decay)
Half-Life
 time required for half of a sample of radioactive
isotopes to break down (decay)
 half-life is always constant for a particular isotope
Half-Life
 parent isotope- original radioactive isotope
 daughter isotope- newly formed stable isotope
Half-Life
 scientists compare the ratio of the parent and
daughter isotopes to calculate absolute age
higher % of daughter isotope = more half-lives
higher % of parent isotope = less half-lives
Radioactive Isotopes
 Uranium-238 (238U): very long half-life (4.5 billion
years)
 useful for dating geologic samples more than 10
million years old
Carbon-14 (14C): short half-life (5730 years)
used to date once living samples less than 70,000
years old
Output Activity (Page 44)
 Illustrate Figure 4 from page 194 of the Holt Textbook
 Create a key to represent the parent and daughter isotopes
 Label each part of the diagram with:
 the % of parent isotope that has decayed into the daughter
isotope
 the % of the parent isotope that has not decayed
Output Activity (Page 44)
 Using the diagram from page 194, answer the following
question. Write both the question and answer.
1) Scientists discover a fossil and use radiometric carbon
dating to find its age. The fossil contains a 3 to 1 ratio of the
daughter isotope, Nitrogen-14, compared to its parent
isotope, Carbon-14. How old is the fossil? (the half-life of
Carbon-14 is 5,730 years)
Extra Credit
 Answer questions #28,29,30 from page 203 in your
textbook.
 Each correct answer earns 3 points on tomorrow’s
Quiz.
 Write your answers on a separate piece of paper and
submit them when you are finished.
 You must show your work!