RELATIVE-AGE DATING Chapter 16 Lesson 2
Pages 574-580
NEW VOCABULARY
Relative Age – the age of rocks and geologic features compared with
other rocks and features nearby.
Superp...
FIND RELATIVE AGE
A.
B. C. D.
FIND THE RELATIVE AGE
FIND RELATIVE AGE
RELATIVE AGES OF ROCKS
Geologists, or scientists that study Earth and rocks, have developed a
set of principles to compare...
RELATIVE AGE AND
SUPERPOSITION
Monday
Tuesday
Wednesday
Thursday
Friday
PRINCIPLES OF RELATIVE
AGE DATING
1. Superposition
2. Original Horizontality
3. Lateral Continuity
4. Inclusion
5. Cross-c...
SUPERPOSITION
Superposition is the principle that in
undisturbed rock layers, the oldest rocks
are on the bottom.
Unless s...
ORIGINAL HORIZONTALITY
The second principle of relative-age
dating is original horizontality.
According to this principle,...
LATERAL CONTINUITY
Another principle of relative-age dating
is that sediments are deposited in large
continuous sheets in ...
CROSS-CUTTING
RELATIONSHIPS
Sometimes, forces within Earth
cause rock formations to break, or
fracture.
When rocks move al...
INCLUSION
Occasionally when rocks form they
contain pieces of other rocks.
This can happen when part of an
existing rock b...
UNCONFORMITIES
After rocks form, they are sometimes uplifted and exposed at Earth’s
surface
 When rocks are exposed, wind...
UNCONFORMITIES
There are three types of
unconformities.
Disconformity
Angular Unconformity
Nonconformity
DISCONFORMITY
Younger sedimentary layers are deposited on top of older, horizontal
sedimentary layers that have been eroded
NONCONFORMITY
Younger sedimentary layers are deposited on older igneous or
metamorphic rock layers that have been eroded.
ANGULAR UNCONFORMITY
Sedimentary layers are deposited on top of titled or folded
sedimentary layers that have been eroded.
CORRELATION
When geologists are faced with
unconformities, gaps in the rock record,
they fill in the gaps by matching rock...
MATCHING ROCK LAYERS
Another word for correlation is
connection.
Sometimes it is possible to connect rock
layers simply by...
INDEX FOSSILS
If scientists want to learn the relative
ages of rock formations that are very
far apart or on different con...
INDEX FOSSILS
Scientists use fossil that existed
for only a short time in many
different areas on Earth, like
trilobites
...
Chapter 16.2: Relative-Age Dating
Chapter 16.2: Relative-Age Dating
Chapter 16.2: Relative-Age Dating
Chapter 16.2: Relative-Age Dating
Chapter 16.2: Relative-Age Dating
Chapter 16.2: Relative-Age Dating
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Chapter 16.2: Relative-Age Dating

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Grade 8 Integrated Science Chapter 12 Lesson 1 on relative-age dating of fossils and rock layers. This lesson explains how scientists use rock layers to determine a age of a rock or fossil compared to others. The goal of this lesson is for students to be able to correctly order rock layers by age and to know the different disconformities and nonconformities.

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Transcript of "Chapter 16.2: Relative-Age Dating"

  1. 1. RELATIVE-AGE DATING Chapter 16 Lesson 2 Pages 574-580
  2. 2. NEW VOCABULARY Relative Age – the age of rocks and geologic features compared with other rocks and features nearby. Superposition – the principle that in undisturbed rock layers, the oldest rocks are on the bottom. Inclusion – a piece of an older rock that becomes part of a new rock. Unconformity – a surface where rock has eroded away, producing a break, or gap, in the rock record. Correlation – matching rocks and fossils from separate locations. Index Fossil – Fossils that represent species that existed on Earth for a short length of time, were abundant, and inhabited many locations.
  3. 3. FIND RELATIVE AGE A. B. C. D.
  4. 4. FIND THE RELATIVE AGE
  5. 5. FIND RELATIVE AGE
  6. 6. RELATIVE AGES OF ROCKS Geologists, or scientists that study Earth and rocks, have developed a set of principles to compare the ages of rock layers. They use these principles to organize the layers of rock according to their relative age. Relative age is the age of rocks and geologic features compared with other rocks and features nearby. *How might you define your relative age?
  7. 7. RELATIVE AGE AND SUPERPOSITION Monday Tuesday Wednesday Thursday Friday
  8. 8. PRINCIPLES OF RELATIVE AGE DATING 1. Superposition 2. Original Horizontality 3. Lateral Continuity 4. Inclusion 5. Cross-cutting Relationships
  9. 9. SUPERPOSITION Superposition is the principle that in undisturbed rock layers, the oldest rocks are on the bottom. Unless some force disturbs the layers after they were deposited, each layer of rocks is younger than the layer below it.
  10. 10. ORIGINAL HORIZONTALITY The second principle of relative-age dating is original horizontality. According to this principle, most rock-forming materials are deposited in horizontal layers. Sometimes rock layers are deformed or disturbed after they form. For example, the layers might be tilted or folded. Even though they might be tilted, all the layers were originally deposited horizontally.
  11. 11. LATERAL CONTINUITY Another principle of relative-age dating is that sediments are deposited in large continuous sheets in all lateral directions The sheets, or layers, continue until they thin out or meet a barrier. A river might erode the layers. But their placements do not change
  12. 12. CROSS-CUTTING RELATIONSHIPS Sometimes, forces within Earth cause rock formations to break, or fracture. When rocks move along a fracture line, the fracture is called a fault Faults and dikes cut across existing rock According to the principle of cross- cutting relationships, if one geologic feature cuts across another, the feature that is cuts across is older. A dike is a sheet of rock that formed in a crack in a pre-existing rock.
  13. 13. INCLUSION Occasionally when rocks form they contain pieces of other rocks. This can happen when part of an existing rock breaks off and falls into soft sediment or flowing magma When the sediment or magma becomes rock, the broken pieces become a part of it. A pieces of an older rock that becomes part of a new rock is called an inclusion. According to the principle of inclusions, if one rock contains pieces of another rock, the rock containing the pieces is younger than
  14. 14. UNCONFORMITIES After rocks form, they are sometimes uplifted and exposed at Earth’s surface  When rocks are exposed, wind and rain start to weather and erode them.  These eroded areas represent a gap in the rock record  Often, new rock layers are deposited on top of old, eroded layers.  When this happens, an unconformity occurs.  An unconformity is a surface where rock has eroded away, producing a break, or gap, in the rock record. An unconformity is not a hollow gap in the rock. It is a surface on a layer of eroded rocks where younger rocks have been deposited. However, an unconformity does represent a gap in time.
  15. 15. UNCONFORMITIES There are three types of unconformities. Disconformity Angular Unconformity Nonconformity
  16. 16. DISCONFORMITY Younger sedimentary layers are deposited on top of older, horizontal sedimentary layers that have been eroded
  17. 17. NONCONFORMITY Younger sedimentary layers are deposited on older igneous or metamorphic rock layers that have been eroded.
  18. 18. ANGULAR UNCONFORMITY Sedimentary layers are deposited on top of titled or folded sedimentary layers that have been eroded.
  19. 19. CORRELATION When geologists are faced with unconformities, gaps in the rock record, they fill in the gaps by matching rock layers or fossils from separate locations. Matching rocks and fossils from separate locations is called correlation.
  20. 20. MATCHING ROCK LAYERS Another word for correlation is connection. Sometimes it is possible to connect rock layers simply by walking along rock formations and looking for similarities. At other times, soil might cover the rocks, or rocks might be eroded away In these cases, geologists correlate rocks by matching exposed rock layers in different locations Through correlation, geologists have established a historical record for part of the southwestern United States.
  21. 21. INDEX FOSSILS If scientists want to learn the relative ages of rock formations that are very far apart or on different continents, they often use fossils. If two or more rock formations contain fossils of about the same age, scientists can infer that the formations are also about the same age. Not all fossils are useful in determining the relative ages of rock layers  Fossils of species that lived on Earth for hundreds of millions of years are not helpful for identifying when a rock was formed
  22. 22. INDEX FOSSILS Scientists use fossil that existed for only a short time in many different areas on Earth, like trilobites  These are called index fossils When an index fossil is found in rock layers at different locations, geologists can infer that the layers are of similar age
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