Name: _____________________ Date: __________________Period: ____
Relative and Absolute Dating Practice
Relative Dating Definitions To Know: Highlight key words from the definitions!
Term
Definition
Relative Age
The age of one object compared
to the age of another object
Law of
Superposition
Each rock layer is older than the
one above it (oldest stuff at the
bottom). This is only true if the
sedimentary rock layers have not
been disturbed.
Intrusion
When a volcanic eruption
(Unconformity) occurs, molten, igneous, rock
forces its way up through the
rock layers above it. The igneous
intrusion is younger than the
layers it cuts across.
Fault
A break in the rocks that make up
(Unconformity) the earth’s crust that is due to the
movement of rock on either side
of the fault
Index Fossil
Fossils of unique organisms that
lived for only a short time period,
but were found over a wide area
of the earth
Picture
A is older than B but
younger than C
1. Find and label examples of each of the following in the diagram below:
Igneous Intrusion Erosion
Fault
Directions: In the following diagrams list the events / rock layers in order from
OLDEST to YOUNGEST
2.
OLDEST: ____ , ____ , _____ , _____ , _____ YOUNGEST
3.
OLDEST: ____ , ____ , _____ , _____ , _____, _____ , _____ , _____ ,
_____ , _____ , _____, _____, ______ YOUNGEST
Directions: Use the information about the known index fossils to determine the
approximate age of the rock layers
Layer L: ________
Layer Z: _______
Layer Q: _______
Layer D: _______
Layer A: _________
Two scientists are doing a geologic dig ­ one in China and the other in North
Carolina. Both come across a layer of rock that is rich in index fossils of trilobites.
What can we say about the rock layers in which they were found?
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A good index fossil is a fossil of an organism that only existed for a brief time
period, but was widespread over the earth. The four pictures shown above are from
four different places on the planet. Which of the fossils ­ A, B, C, or D ­ would be the
best index fossil. Explain.
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Absolute Dating Practice
1. What parent isotope would scientists most likely use to date fossilized whale bones
from 70,000 years ago?
2. What daughter isotope does Uranium­238 become when it decays?
3. How long does it take half of the potassium­40 ions to decay to argon­40? Label the
graph below ­ which line represents potassium? which line represents argon?
4. A scientist discovers a rock in Greenland that contains trace amounts of zircon.
The zircon contains about 50% U­238 atoms, and 50% Pb­206 atoms. How old is the
rock?
5. A scientist discovers a volcanic rock in South Africa. The rock contains about 25%
K­40 atoms, and 75% Ar­40 atoms. How old is the rock?