Time scale PDF

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geologic time scale...

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1. Place the lettered features in proper sequence, from oldest to youngest in space provided on the figure. Youngest

Oldest

K basalt L J granite Fault N I H G F Fault M E D C B A

2. What type of unconformity separates layer G from layer F? Disconformity separates between layer G and F as layers are parallel to each other and older rocks were exposed and there is erosion surface present. 3. Which principle of relative dating did you apply to determine that rock layer H is older than layer I? According to law of superposition it is stated that older layer is at bottom and younger layer is at top in undisturbed strata, that’s why H is older than layer I. 4. Which principle is of relative dating did you apply determine that fault M is older than rock layer F? The principle of cross cutting could be applied as fault M have not cross cut the layer above it which is layer F 5. Explain how you know that fault N is older than igneous intrusion J. Fault N has been cross cut by the granite J which illustrates that fault N is older than igneous intrusion J. 6. If rock layer F is 150 million years old and layer E is 160 million years old, what is approximate age of fault M? The approximate age of fault M will be 155 million years old as it is older than layer F and younger than layer E 7. The analysis of sample from layer G and F indicates the following proportions of parent materials to daughter product. If the half-life of parents is known to be 75 million, what are the ages of two layers?

Parent

daughter

Age

Layer G

50%

50%

75 million

Layer F

25%

75%

150 million

8. What time interval is represented by the disconformity at the base of layer G Time Interval form 150 million to 75 million. 9. What fraction of time is represented by Precambrian The age of earth is approximately 4600 million and Precambrian constitutes 4060 million and remaining is 600 million so Precambrian constitutes around 88 percent of fraction. 10. Examine the photograph in figure 6.22. Describe as accurately as possible, the relative geologic history of area, using principles of relative dating covered in this exercise. According to law of original horizontality all the layer were deposited initially horizontal which are layers G,F,E and D. First the layer G was deposited followed by the layer F, layer E and then layer D were deposited. Layer D followed the lateral continuity principle and eventually thins out. After that that tectonic forces tilted the strata and exposed to the surface which caused erosion and formed unconformity as showed by layer C. After that sea level rised again and deposition started and layer B and layer A was deposited which are at angle to layers G,F,E and D which is marked as angular unconformity.

The purpose of this problem is to illustrate how numerical ages based on radioactivity can be determined graphically. a. Complete columns A and B in the table that follows. For example, after one half-life, the parent fraction is 0.5 and the daughter fraction is 0.5; after two half-lives, the parent fraction is 0.25 and the daughter fraction is 0.75. Remember, the sum of the two fractions must equal 1.0. b. Next, complete column C in the table by dividing values in Column B by corresponding values in Column A. For example, for one half-life elapsed, (Col. B)/(Col. A) = 0.5/0.5 = 1.

Half-life elapsed

A. Parent Fraction

0 1 2 3 4 5

B. Daughter Fraction

0.5 0.25 0.125 0.0625 0.03125

C. Daughter/parent ratio 0 1 3:1 7:1 15:1 31:1

0.5 0.75 0.875 0.9375 0.96875

C Using Figure 13.11 and the data in the preceding table, construct a graph in which the vertical axis is “ Daughter-Parent Ratio” and the horizontal axis is “ Half-Lives Elapsed.” The point representing one half-life is already plotted. Plot the rest, and draw a smooth curve connecting the data points; that is, do not connect the points with straight-line segments, but estimate the curvature between points as best as you can so that the entire curve bends smoothly.

Chart Title 35

31

30

Nd/Np

25 20 15

15 10

7

5 0

0

3

1

0 0.5

1

1.5

2

2.5

3 T1/2

3.5

4

4.5

5

5.5

d. For samples 1-3 in the following table, first calculate and record the daughter-parent ratio, ND /Np. Then, using your graph in Figure 13.11, determine the number of halflives that have elapsed for each sample and write your answer in the “Half Lives Elapsed” column. e. If the half-life is 8200 years, calculate the age in years of the samples in the preceding table and write your answer in the “Age in Years” column. Show your work.

Sample number

Atoms of parent NP

1 2 3

2135 4326 731

Atoms of daughter ND 3203 10815 14620

ND/NP 1.5 2.5 20

Half-life elapsed 1.33 1.8 4.36

Age (years) 10906 14760 36490...