Name______________________________________ Period____________ Date___________
Earth and Space Science/Honors
Geologic Time
Geologic Time Review
Base your answers to questions 1 through 5 on the geologic cross section below. Numbers 1
through 17 identify rock layers and Q represents a fault. Lines W, X, Y, and Z are locations of
unconformities. The rocks have not been overturned.
1. Which rock or feature is oldest? ______________
2. What kind of unconformity exists at letter Z? ____________________
3. What kind of unconformity exists at letter X? ____________________
4. What kind of unconformity exists at letter Y? ____________________
5. List the order of geologic events represented in the cross section from oldest to youngest.
1. ___________________________
8. ___________________________
2. ___________________________
9. ___________________________
3. ___________________________
10. __________________________
4. ___________________________
11. __________________________
5. ___________________________
12. __________________________
6. ___________________________
13. __________________________
7. ___________________________
14. __________________________
6. List the order of geologic events represented in the cross section from oldest to youngest.
1. _________________________________________
2. _________________________________________
3. _________________________________________
4. _________________________________________
5. _________________________________________
6. _________________________________________
7. _________________________________________
8. _________________________________________
9. _________________________________________
10. ________________________________________
Use the diagram below to answer questions 7 through 12.
7. Place the above 10 rock units/events (A-J) in order from oldest to youngest:
Oldest _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ Youngest
8. What two geologic laws/principles did you use to determine the age of rock units D-J-I-A-G?
9. What geologic law/principle did you use to determine the age of rock Unit F relative to Unit
G?
10. Which two units represent igneous intrusions?
11. a. The boundary between Units (G-A-I) and Unit E is called a(n): ______________________
Be specific!
11.b. What does it represent?
12. The boundary between Unit C and Unit H is called a(n): ______________________
Use the diagram below to answer questions 13 through 15.
13. Place the above 7 rock units/events (A-J) in order from oldest to youngest:
Oldest _____ _____ _____ _____ _____ _____ _____ Youngest
14. Which sedimentary rock layer is older, A or B? Explain your answer and name the scientific
law that you applied to reach your conclusion.
15. G began as magma that hardened underground to form igneous rock. What is the age of G
in relation to C? What term applies to bodies of rock such as G?
Use the cross-section below to answer questions 16 through 18.
16. Which rock unit is younger, the Erie coal
or the Bullet shale?
17. Between which two units is there an
unconformity?
18. What type of unconformity is it?
19. A particular rock sample contains 6.25% of the parent element Carbon-14 and the remaining
93.75% of the sample has decayed into the stable daughter element. How old is this rock?
20. A rock sample contains 2.5 g of the radioactive element Potassium-40. How old would the
sample be if the rock originally contained 20 g of the parent Potassium-40?
21. A particular rock sample contains 25% of the parent element Uranium-235 and the
remaining 75% of the sample has decayed into the stable daughter element. How old is this
rock?
22. If you had a 30 g sample of Americium-241, how much parent material would remain after
1299 years?
23. How many half-lives have passed if a particular rock sample has 75% of its parent element
and 25% of its daughter element?
24. A sample of basalt includes zircon crystals containing the radioactive isotope Uranium-235,
which decays into the stable element, Lead-207. The zircon crystals have 98.44% of the original
U-235 remaining, and 1.56% has decayed into Pb-207. How old are the crystals?
25. The radioactive element is Uranium-238 and its daughter element is Pb-206. What is the
age of a granite outcrop, if the sample has crystals with 99.22% of the parent element and
0.78% of Pb-206?
Directions: Use the information in the geologic time scale, which shows major events in geologic
history, to answer the questions on the following pages.
26. What two periods of geologic history had mass extinctions occur?
27. The Pennsylvanian and Mississippian Periods is also called the
_____________________________ Period.
28. What geologic period has the first fossil evidence of insects in the rock record?
________________________________
a. When did the period start?
________________________________
b. When did it end?
________________________________
c. How long did that period last?
________________________________
29. What geologic period has the first fossil evidence of shelled organisms in the rock record?
________________________________
a. When did the period start?
________________________________
b. When did it end?
________________________________
c. How long did that period last?
________________________________
30. What geologic period has the first fossil evidence of human fossils in the rock record?
________________________________
a. When did the period start?
________________________________
b. When did it end?
________________________________
c. How long did that period last?
________________________________