Earth Systems
Study Guide – Ch 12 & 13-KEY
1. Order from oldest to youngest.
Oldest- 4
5
2
6
1
Youngest- 3 (because of cross-cutting)
Oldest-E
G
L
C
H (fault)
M
D
J
A
N
K
B
Youngest-F
---------- Rock inclusions
These are older than rock B, Rock A
formed 1st.
2. Describe the principle of inclusion-Fragments of a rock which are included in another (host)
rock must be older than the host rock.
3. Describe the principle of cross-cutting –When a geologic feature cuts into another geologic
feature, the one that cuts into is the youngest.
4. Describe the principle of superposition-In a sequence of sedimentary rock, each layer is older
than the one above it.
5. In what type of rock are fossils found? Sedimentary
6. Describe and give examples of trace fossils- A trace fossil is a trace of the animal, not a fossil of
the animal itself. Examples are a footprint, trail or burrow fossil.
7. What two conditions are most favorable for fossil preservation? Quick burial and possession of
hard parts
8. Describe fossil correlation and be able to analyze the following picture. Fossil correlation is
using fossils to match up rocks of similar ages in different areas.
Which organism existed over the longest expanse of time? The last one
9. What is a half-life? Half-life is the time it takes for 50% of the nuclei in a radioactive sample to
decay.
10. Be able to calculate half-life!! (See attached practice problems on the last page)
11. What happens to unstable nuclei during radioactivity? They break apart (decay).
12. What is the geologic time scale? Geologists have divided Earth’s time into manageable parts.
13. Which time expanse is the longest? Eon.
14. How old is Earth? 4.56 billion years
15. Understand and be able to answer questions about this chart.
*When ½ of the parent element remains, ½ of the daughter element has formed.
* When 1/8 of the parent element remains, 3 half-lives have occurred.
16. Put epoch, period, eon and era in order from largest to smallest block of time.
Eon, era, period, epoch
17. Some continents contain large core areas of Precambrian rocks called ___shields___.
18. At the end of which time era did Pangaea fuse together? Paleozoic
19. _Amphibians____ were the first animals to live on land.
20. What geologic time period are we currently in? Quaternary
21. What was missing in Earth’s original atmosphere? Oxygen
22. Put the following in order of occurrence: Cenozoic, Paleozoic, Precambrian, Mesozoic
Precambrian, Paleozoic, Mesozoic, Cenozoic
23. Where did life first occur in the early Paleozoic? The seas
24. What major animals became extinct at the end of the Mesozoic time era? Dinosaurs
25. The “Age of Mammals” followed what major event? The extinction of dinosaurs
26. Dinosaurs lived during which era? Mesozoic
27. 88% of Earth’s history is in which time frame? Precambrian
28. What evolutionary development led to reptiles dominating land over amphibians?
They lay eggs on land.
29. Describe characteristics of mammals. Give birth to live young, have hair, they regulate their
own body temperature.
30. Be able to read the following diagram:
**Figure 13-1 shows the times of appearance and relative abundance of major groups of
organisms. The wider the band, the more dominant the group. According to Figure 13-1, which
plant group dominates the Cenozoic era? Flowering plants
**Figure 13-1 shows the times of appearance and relative abundance of major groups of
organisms. According to Figure 13-1, the fossils of which type of organism would be
characteristic of the Precambrian era? Algae
31. Why did birds evolved rapidly during the Cenozoic era? Because flowering plants flourished
32. What caused many events of mountain building, volcanism and earthquakes in western North
America during the Cenozoic? Plate interactions
33. Which title best describes the current geologic age? Age of Mammals
34. The geological processes that shape Earth’s features today are basically the same as they were
in the geologic past .
35. Petrified wood is an example of what type of fossil? Altered remains
36. Organisms with hard parts stand a good chance of being fossilized if they are _rapidly buried by
sediment___.
37. In which of the following environments would the shell of an organism most likely be preserved
as a fossil? At the bottom of a lake, buried by a landslide.
38. What must be true for a fossil organism to be useful as an index fossil?
The fossil organism must be widespread geographically.
The fossil organism must be abundant.
The fossil organism must be limited to a short span of geologic time.
39.
40.
41.
42.
The process by which atomic nuclei spontaneously decay is called radioactivity.
Atoms with the same atomic number but different mass numbers are called isotopes.
The radiometric dating of an igneous rock provides a date for when the rock formed.
Radiocarbon dating is used to date recent geologic events up to 75,000 years ago.
Half-Life practice problems
**Remember: Half-life is the amount of time it takes for your sample to divide in half 1 time.
1. Sodium-24 has a half-life of 15 hours. How much Sodium-24 will remain in an 18.0 g sample
after 60 hours?
18g ------------------------------ 9g
9g ------------------------------- 4.5 g
4.5g ----------------------------2.25 g
2.25g --------------------------- 1.125 g
=15 hrs (1 half-life)
=15 hrs (2 half-lives)
=15 hrs (3 half-lives)
=15 hrs (4 half-lives)
60 hrs
2. After 42 days a 2.0 g sample of phosphorus-32 contains only 0.25 g of the isotope. What is the
half-life of phosphorus-32?
2g ---------------------------------------- 1g
1g ----------------------------------------0.5 g
0.5g ------------------------------------ 0.25 g
=? (1 half-life)
=? (2 half-lives)
=? (3 half-lives)
42 days =
42 days ÷ 3 half-lives= 14 days
3. Polonium-214 has a relatively short half-life of 164 seconds. How many seconds would it take
for 8.0 g of this isotope to decay to 0.25 g?
8.0g ------------------------------------------------- 4.0g
4.0g ------------------------------------------------- 2.0g
2.0g ------------------------------------------------- 1.0g
1.0g ------------------------------------------------- 0.5g
0.5g ------------------------------------------------- 0.25g
= 164 secs (1 half-life)
= 164 secs (2 half-lives)
= 164 secs (3 half-lives)
= 164 secs (4 half-lives)
= 164 secs (5 half-lives)
820 secs
3. How many days does it take for 16 g of palladium-103 to decay to 1.0 g? The half-life of
palladium-103 is 7 days.
16g -------------------------------------- 8g =17 days (1 half-life)
8g --------------------------------------- 4g = 17 days (2 half-lives)
4g ------------------------------------------- 2g =17 days (3 half-lives)
2g ------------------------------------------- 1g =17 days (4 half-lives)
68 days