12.3 - Dating With Radioactivity

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List the order of events that took
place earthquake deposit D deposit B deposit
G intrusive lava rocky deposit R river cuts
through deposit E deposit A
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Dating With Radioactivity

• Basic Atomic Structure
• There are protons and neutrons in an atoms
  nucleus.
• The number of neutrons in an atom can vary -
  these are called isotopes.
• Radioactivity
• When nuclei are unstable, they break apart, or
  decay, in a process known as radioactivity.

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• An unstable or radioactive isotope is called a
  parent.
• The isotopes that result from the decay of the
  parent are called daughter products.
• Half-Life
• A half-life is a common way of expressing the
  rate of radioactive decay.
• A half-life is the time required for one half of
  the atoms of a radioactive substance to decay.
• HALF-LIFE GRAPH

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Number ofhalf-liveselapsed Fractionremaining Percentageremaining Percentageremaining
0 1/1 100
1 1/2 50
2 1/4 25
3 1/8 12 .5
4 1/16 6 .25
5 1/32 3 .125
6 1/64 1 .563
7 1/128 0 .781
... ... ... ...
n 1/2n 100(1/2n) 100(1/2n)
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Say what!?!?

• A 100g sample of Millsonite has a half-life of 5
  years.
• After 5 years - 50 grams remain
• After 10 years - 25 grams remain
• After 15 years - 12.5 grams remain
• After 20 years - 6.25 grams remain

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• Radiometric Dating
• Radiometric dating is the procedure of
  calculating the absolute ages of rocks and
  minerals that contain radioactive isotopes.
• Dating with Carbon-14
• Radiocarbon dating is the method for determining
  age by comparing the amount of Carbon-14 to the
  amount of Carbon-12 in a sample.

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So what!

• Importance of Radiometric Dating
• Radiometric dating has been used to date
  thousands of events in Earths history.
• Rocks on Earth have been dated to be as much as 4
  billion years old.

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Classwork/Homework PRACTICE

• Finding absolute age of a rock.
• BOOK p. 327
• Determine D/P ratio
• Practice problems