1­11 Relative Age.notebook
January 11, 2012
Wednesday, January 11
1. Please have your homework out and ready to go! 2. Turn your blue sheets into the basket if signed. 3. Answer the question below on a scrap piece of paper:
What is the difference between
relative age and absolute age?
What is the difference between relative age and absolute age?
Relative age describes the age of rock compared to the ages of other rocks, but absolute age is the exact number of years since the rock formed.
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1­11 Relative Age.notebook
January 11, 2012
3. According to the law of superposition, the __________________________________ layer is at the bottom. Each higher layer is _____________________ than the layers below it. 4. Is the following sentence true or false? The deeper one travels into the Grand Canyon, the younger the rocks become. _________________________
What clues tell geologists
Clues
How it forms
extrusion
in undisturbed areas, when lava cools and extrusions are always solidifies on top of younger than the rock older rock formations
layers below them
intrusion
when molten rock cools and solidifies within pre­existing rock
fault
break in Earth's crust the fault is always younger than the usually caused by geologic forces within youngest layer of rock Earth
cut by the fault
an intrusion is always younger than the layers of rock it pierces
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1­11 Relative Age.notebook
January 11, 2012
g. A fault cuts through an extrusion. Which layer is the older? ___________________________
6. What is an unconformity? the area where the processes of weathering, erosion, deposition, and lithification have caused a gap in the geologic record
8. index
9. Circle the letter of each sentence that is true about index fossils. a. index fossils must be found in many different areas.
b. index fossils must represent an organism that lived for a very long time. c. index fossils tell the absolute ages of the rock layers in which they occur.
d. a type of ammonite that is different from other ammonites is a useful index fossil.
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1­11 Relative Age.notebook
January 11, 2012
1. What is the youngest rock layer? Explain.
Layer C is the youngest rock layer. It is found towards the top of the layers making it the youngest. 2. Is the extrusion older or younger than rock layer B. Explain
The extrusion is younger than rock layer B because extrusions are always younger than the rock layers below them. 3. Is the fault older or younger than rock layer A? Explain.
Younger because a fault is always younger than the youngest layer of rock cut by the fault. 4. How could a geologist use the fossil in rock layer B to date a rock layer in another location?
The geologist could find out how old the fossil is in layer B. He could then compare that to another rock layer to see how old it is.
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1­11 Relative Age.notebook
January 11, 2012
_________ 5. fault
_________ 6. extrusion
_________ 7. unconformity
_________ 8. relative age
_________ 9. law of superposition
_________ 10. intrusion
_________ 11. absolute age
_________ 12. index fossil
Which came first?
2. Use the letters in the diagram to list the order in which the layers formed.
D,J,C,B,A,F,G,H,I,E
3. What might explain layer E?
an intrusion cut through the layers
4. How do you know layer C formed before layer B?
before the layers were tilted, C would have been below B
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1­11 Relative Age.notebook
January 11, 2012
5. List the letters of the layers that show a break in the rock record.
E, D, J, C, B, A, F
6. Describe what happened in this geologic column.
the rock layers were tilted (D, J, C, B, A) and an intrusion cut across all the layers. 6