Transcript Radioactive Dating

Radioactive Dating
Section 10.3
Radioactive Decay
• Since rocks are made of matter, they
contain atoms
• Most elements are stable but some are
unstable.
• Unstable (radioactive) elements will
break down (decay) to form stable
elements.
• Using this property we can determine
the absolute age of a rock
Radioactive Decay
• The rate of decay of each radioactive
element is constant. (half-life)
• A half-life is the time it takes for half the
atoms to decay.
Energy
Stable atom
Unstable atom
Particles
Radioactive Decay
%
Radioactive
Material
Remaining
100
90
80
70
60
50
40
30
20
10
0
Start
1
2
3
Number of Half-Lives
4
Radioactive Decay
Different elements have different half-lives
Radioactive Element
Half-life (years)
Carbon-14
5,730
Potassium-40
1.3 billion
Rubidium-87
46.8 billion
Thorium-232
14 billion
Uranium-235
713 million
Uranium-238
4.5 billion
Radioactive Decay Activity
Directions:
Take a square and cut it in half. Put one
piece aside. Note each time you cut the
paper.
Cut the piece you have in half and set one
piece aside again.
Continue this until you can not practically
cut the square any more.
Radioactive Decay Activity
1)What is the total number of times you
were able to cut the sample in half?
2)Each cut represents the half-life of
Carbon-14. What is the length of time
represented by each cut?
3)Multiply the number of cuts by the halflife period of C-14. What is the total
amount of time represented by all your
cuts?
Radioactive Decay Activity
4) If an animal lived million of years ago,
could C-14 be used to determine when it
died? Why or why not?
5) If an animal lived near the La Brea Tar
Pits (found now in Los Angeles) 40,000
years ago, could C-14 be used to
determine when it died?