Homework Review
Pg. 190 #1-8 , 4 ways to determine absolute age
HW pg. 190 #1-8
1. Why is it important for scientists to be able to
determine the relative age of rocks?
So that they can understand the age and history of the
Earth. What events came before and after one
another.
2. State the principle of uniformitariansm in your own
words.
The same processes and events have occurred
throughout time in the same way.
HW pg. 190 #1-8
3. Explain how the law
of superposition
can be used to
determine the
relative age of
sedimentary rocks.
HW pg. 190 #1-8
4. Explain the difference between an unconformity and
a nonconformity.
-An unconformity is any break in the geological record
-A nonconformity is a type of unconformity where
Metamorphic or igneous rock layers are covered with layers
of sedimentary rock
Nonconformity: part of the geological record are missing
HW pg. 190 #1-8
5. Compare an angular unconformity with a
disconformity.
HW pg. 190 #1-8
6. Describe how the law of crosscutting relationships
helps scientists determine the relative ages of rocks.
HW pg. 190 #1-8
7. Which would be more difficult to recognize: a
nonconformity or a disconformity? Explain your
answer.
A disconformity would be harder because it has horizontal layers of sedimentary rock on
both sides of the boundary. A nonconformity can be identified by the presence of
metamorphic or igneous rock below the unconformity
HW pg. 190 #1-8
8. Crosscutting relationships.
HW. 4 ways to determine absolute age of rock
formations
Rates of erosion
• study erosion rates today (principle of
uniformitarianism), should be similar to past rates
•for newer formations (past 10,000-20,000 years)
Rates of deposition
•average about 30 cm of sedimentary rock deposited
over 1,000 years
• not all sediments deposited at an average rate (e.g.
storms)
HW. 4 ways to determine absolute age of
rock formations
Varve count: annual layers can be counted
Usually form in glacial lakes
Coarse summer layer covered by fine
winter layer
HW. 4 ways to determine absolute age of rock
formations
Radiometric dating. Use the known rate of radioactive
decay to estimate age of rocks by their composition
• decomposition of isotopes of an element