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Science 7
Unit 2
Earth & Life History
Name: ______________________________
Date: ______________ Period: __________
Sec 5.1 Rocks Provide a Timeline for Earth
Vocabulary
relative age
rock cycle
index fossil
absolute age
half-life
Changes in rocks provide a record of the past.
1. What is relative age ?
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The three main types of rocks form in different ways.
2. Describe the three main types of rocks.
a. Sedimentary: __________________________________________________________________
b. Igneous: ______________________________________________________________________
c. Metamorphic: __________________________________________________________________
3. What is the rock cycle? _________________________________________________________________
Layers of sedimentary rock show relative age.
4. Examine the diagram below that shows a sequence of rock that has been disturbed. Which layer of rock
is the oldest? Which is the youngest?
oldest________________________________
youngest______________________________
Explain.
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Igneous Rock and Sedimentary Layers
5. Examine the diagram above. Which rock unit is the youngest?
Explain.___________________________________________________________________
6. In the disturbed layers of sedimentary rock shown above, which is older—layer D or intrusion 1?
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Index Fossils
7. How do scientists use index fossils to determine the age of a rock layer?
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Radiometric dating can show absolute age.
8. What is absolute age? How does it differ from relative age?
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Half-Life
9. What is half-life used for? Give an example.
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Using Absolute and Relative Age
10. How can scientists use igneous rock to date sedimentary rock?
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11. A geologist used radiometric dating to calculate the age of a piece of sandstone.
How would the actual age of the rock compare to the age determined by the geologist? Why?
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