1. Bellwork is on your notes today!!!!!

2. Radiometric Dating quantifies (calculates) the date in years.
Bellwork: Fri. Feb 17, 2017
How do we determine the age of a rock or fossil within that rock?
Relative dating – Uses relative position of fossils to one another and the rock layers "A is older than B“
Radiometric Dating quantifies
(calculates) the date in years.
Also called Absolute Dating

3. Relative Dating: establish the relative ages of rock layers with Index fossils
If the same index fossil is found in two widely separated rock layers, the rock layers are probably similar in age.

4. So far we have been looking at the relative time scale
So far we have been looking at the relative time scale. How are numbers added to the time scale? How have geologists determined that:
Earth is about 4.6 billion years old?
The oldest known fossils are from rocks that were deposited about 3.5 billion years ago?
The first abundant shell fossils occur in rocks that are about 570 million years old?
The last ice age ended about 10,000 ago?

5. The universe is full of naturally occurring radioactive elements.
Radioactive atoms are unstable and break down or “decay” over time from radioactive “parent atoms” into stable “daughter atoms.”

6. Afterwards, they decay at a predictable rate.
When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside.
Afterwards, they decay at a predictable rate.
By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.

7. K=potassium
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8. Radioactive elements in Earth’s rocks can be used as geologic clocks which decay at a constant rate.
From this, geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements.

9. Principles of Radiometric Dating
Naturally-occurring radioactive materials break down into other materials at constant known rates. This is known as radioactive decay. Radioactive parent elements decay to stable daughter elements. .

11. Many radioactive elements can be used as Geologic Time Clocks
Many radioactive elements can be used as Geologic Time Clocks. Each radioactive element decays (breaks down) at its own nearly constant rate.
Once this rate is known, geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements.

12. Elements with various numbers of neutrons are called isotopes of that element.
A half-life is the time it takes for half of the parent radioactive element to decay to a stable daughter element. Each radioactive isotope has its own unique half-life.

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16. 
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18. Half Lives for Radioactive Elements
Radioactive Parent
Stable Daughter
Half life
Potassium 40
Argon 40
1.25 billion yrs
Rubidium 87
Strontium 87
48.8 billion yrs
Thorium 232
Lead 208
14 billion years
Uranium 235
Lead 207
704 million years
Uranium 238
Lead 206
4.47 billion years
Carbon 14
Nitrogen 14
5730 years

19. Radioactive decay occurs at a constant exponential or geometric rate
Radioactive decay occurs at a constant exponential or geometric rate. The rate of decay is proportional to the number of parent atoms present.

20. So scientists can use radioactive decay to assign an absolute age to rocks.
Some elements are radioactive and steadily break down into nonradioactive elements. 20

21. Carbon-14 Dating
Carbon-14 begins to decay when an organism dies.
Carbon-12 is not radioactive and does not decay. It
Is the stable form of thecarbon element
by comparing amounts of carbon-14 and carbon- 12 in a fossil, researchers can determine when the organism lived.
Carbon 14 DECAYS in to Nitrogen 14
However: Carbon-14: half-life of 5730 years is useful only for
organisms less than
60,000 years old.
Carbon 14 has 8 neutrons, 6 protons N
99% of the carbon is carbon-12, 1% is carbon-13, and carbon-14 occurs in trace amounts, e.g. making up as much as 1 part per trillion ( %) of the carbon in the atmosphere 21

22. With a half-life of 5730 years, Carbon-14 is useful only for organisms less than 60,000 years old.

23. Half Life Chart (to figure out parent to daughter element ratios by # of half lives that have passed) 1 2 3 4 5 6 7 8 9 10
1/2
100%
50%
0:1
1:1

24. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
100%
50%
25%
0:1
1:1
3:1

25. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
100%
50%
25%
12.5%
0:1
1:1
3:1
7:1
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26. IF a bone has 64 parts of the daughter element to 1 part of the radioactive parent element how many half lives have passed?________ Using Carbon 14 (half life 5730) how old is this bone? _______________ 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
100%
50%
25%
12.5%
6.25%
0:1
1:1
3:1
7:1
15:1

27. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
100%
50%
25%
12.5%
6.25%
3.125%
0:1
1:1
3:1
7:1
15:1
31:1

28. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0:1
1:1
3:1
7:1
15:1
31:1
63:1

29. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1

30. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1

31. IF a bone has 64 parts of the daughter element to 1 part of the radioactive parent element how many half lives have passed?________ Using Carbon 14 (half life 5730) how old is this bone? _______________ 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1

32. IF a bone has 64 parts of the daughter element to 1 part of the radioactive parent element how many half lives have passed?________ Using Carbon 14 (half life 5730) how old is this bone? _______________ 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

33. Help Starting the Worksheet…
A. Shade in how much carbon-14 is remaining in dinosaur 1 if it were to die right now.
B. How much of dinosaur 1 did you shade in?

34. IF a bone has 64 parts of the daughter element to 1 part of the radioactive parent element how many half lives have passed?________ Using Carbon 14 (half life 5730) how old is this bone? _______________ 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

35. A. Shade in how much of carbon-14 is remaining in dinosaur 2 if it died 5,730 years ago. B. What fraction of dinosaur 2 did you shade in?

36. IF a bone has 64 parts of the daughter element to 1 part of the radioactive parent element how many half lives have passed?________ Using Carbon 14 (half life 5730) how old is this bone? _______________ 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

37. A. Shade in how much carbon-14 is remaining in dinosaur 3 if it died 28,650 years ago. B. What fraction of dinosaur 3 did you shade in?

38. A. Shade in how much carbon-14 is remaining in dinosaur 4 if it died 17,190 years ago. B. What fraction of dinosaur 4 did you shade in?

39. A piece of fossilized bark shows that 1/10th of one carbon-14
half-life has passed. How old is the of bark? Show work below. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

40. IF a bone has 64 parts of the daughter element to 1 part of the radioactive parent element how many half lives have passed?________ Using Carbon 14 (half life 5730) how old is this bone? _______________ 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

41. pottery? Show your work below.
Pottery has been found at an archeological dig. It is shown that 1/16th of one carbon-14 half-life has passed. How old is the
pottery? Show your work below. 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

42.
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43. Bellwork: Mon. Feb. 20, 2017 Radiometric
1. _______________ or Radioactive dating is the use of half-lives to determine the age of a sample.
2. _______________ dating places rocks in sequence in which they were formed.
3. ________-_______length of time required for half of the radioactive atoms in a sample to decay.
Radiometric
Relative
Half life 43

44. Radioactive parent element decays into a stable daughter element
Half-Life paper cutting.
Radioactive parent element decays into a stable daughter element 1 2 3 4 5 6 7 8 9 10
1/2
1/4
1/8
1/16
1/32
1/64
1/128
1/256
1/512
1/1024
100%
50%
25%
12.5%
6.25%
3.125%
1.56%
0.781%
0.39%
0.195%
0.0975%
0:1
1:1
3:1
7:1
15:1
31:1
63:1
127:1
255:1
511:1
1023:1

45. Small-Scale Investigation: Radioactive Decay
Radioactive elements decay at a constant, measurable rate. The time it takes for half of any given amount of an original element to change into a new isotope or element is called a half-life. You can demonstrate the principle of radioactive decay with a simple model.
Materials: clock or watch with a second hand; sheet of notebook paper, about 28 x 22 cm; scissors
Procedure
1. Record the time.
2. Wait 20 seconds, then carefully cut the sheet of paper in half. Select one piece, and set the other piece aside.
3. Wait 20 seconds, then cut the selected piece of paper in half. Select one piece, and
set the other piece aside.
4. Repeat Step 3 until nine 20-second intervals have elapsed.

46. Analysis and Conclusions
1. In terms of radioactive decay, what does the whole piece of paper used in this investigation represent?
2. What do the pieces of paper that you set aside in each step represent? ____________________________
3. What is the half-life of your “element”? (in seconds)_____
4. How much of your paper “element” was left (in %) after the first three intervals? _______
after six intervals? _________
after nine intervals?________
5. What two factors in your model must remain constant for your model to be accurate? Explain your answer.

47. Notes: back of Radiometric Notes
Bracketing the fossils Fossils are usually found in sedimentary rock—not igneous rock.
Sedimentary rocks can be dated using C14 (radioactive carbon dating), but because carbon decays relatively quickly, this only works for rocks younger than about thousand years.
de_o_0/radiodating_01

48. To date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.
Scientists date igneous rock using elements that are slow to decay, like uranium and potassium.

49. Bracketing: dating fossils by “sandwiching” igneous rock layers to determine youngest & oldest ages within the sedimentary rock layer.

50. Bellwork: Tues. Feb. 21, 2017
Use the figure to answer questions 1 through 4
1. The half-life of this parent isotope is _____
2. Percent of parent
isotope remaining after 2
million years will be _______
3. By the 3rd half-life, how
muchof the parent isotope
remains?________
4. How many half-lives are
represented in the graph? ___ 50

51. Bellwork Friday: Feb. 19, 2010 Layers A & C are igneous rock &
have been radiometrically dated.
Layer B is sedimentary & older
than 60,000 years…so
Approximately how old is layer B?
2. What is the technique used to date
layer B (think “rock sandwich or [ ]”)?
If radiometric dating was not available what conclusion could you still make about the age of layers A, B, and C (think about the other type of dating rocks)?
Look at your Geologic Time Scale:
4. What era and period is layer B from?
5. What major evolutionary event involving plants occurred in this period? 51

52. Draw this in your notes:
A m.y.a.
Igneous
B ?
Sedimentary
C m.y.a.
Rock Layers