Download - Relative Dating
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Relative Dating• Relative Age: the age of something compared to
something else.
• Absolute Age: the actual age of a rock or an event
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The Principal of Superposition• In undisturbed sedimentary rock layers (strata),
the oldest rock is at the bottom.
YOUNGEST rock layer
OLDEST rock layer
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Dating Intrusions, Extrusions, & Inclusions
• Intrusion: when magma squeezes into preexisting rocks and cools.– YOUNGER than any rock it cuts through
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Dating Intrusions, Extrusions, & Inclusions
• Extrusion: when lava flows on the SURFACE and cools.– YOUNGER than rocks beneath it– OLDER than rocks above it.
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Dating Intrusions, Extrusions, & Inclusions
• Inclusion: a piece of older rock within igneous rock.
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Cross-Cutting Relationships• Types of Cross-cutting relationships: Intrusions,
faults, veins, etc. – These features are YOUNGER than the rocks they cut
across.
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Cross-Cutting Relationships A fault is younger than
the rock layers it cuts across
An igneous intrusion is younger than the rockit penetrates
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The folding and tilting of rock layers are events that are younger than the rock layers
they effect.
Dating Rock Features
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Unconformity – A surface of erosion between rock layers that represents a missing gap in Earth’s history.
Deposition Uplifting and folding
Erosion SubsidenceUnconformity
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Correlation• The process of showing that rock layers, or
geologic events, from different places are the same, or similar in age.
• Types of Correlation:1. Exposed bedrock2. Similarities in Rocks3. Use of Index Fossils4. Volcanic Ash or Meteorite Deposits
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1. Correlation by Exposed Bedrock• Bedrock is usually
covered with soil, but can occasionally be exposed.– Correlation can be
accomplished by directly following the rock layers.
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2. Correlation by Similarities in Rocks• Rocks can be correlated by having similar
appearance, color, mineral composition, and rock sequence.
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3. Correlation by Index Fossils• Index Fossil: a fossil that is used to date the rock
layers in which it is found.1. An organism that lived during a relatively short,
well-defined time span.2. Have a wide distribution geographically.
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Which of these is an INDEX FOSSIL?
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4. Correlation by Volcanic Ash and Meteorite Deposits• Volcanic Ash: ash from each volcanic eruption has
unique composition– Ash deposits are widely distributed, and represent a
small period of time.
• Meteorite Deposits: rock particles and debris produced by an asteroid, comet, or meteorite impact can cover large areas of Earth.
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“SEQUENCE OF EVENTS”PRACTICE WORKSHEETS
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Sequence 1: Uplift & Erosion
1. Limestone deposited2. Sandstone deposited3. Shale Deposited4. Uplift5. Erosion
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1. Limestone deposited
2. Sandstone deposited
3. Shale deposited4. Faulting
Sequence 2: Faulting
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Sequence 3: Folding
1. Limestone deposited2. Sandstone deposited3. Shale deposited4. Folding
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Oldest- Limestone
Youngest- Igneous Intrusion
Oldest- Shale
Youngest- Siltstone
Oldest- Sandstone
Youngest- Shale
Oldest- Sandstone
Youngest- Igneous Intrusion
Oldest- Shale
Youngest- Folding
Oldest- Shale
Youngest- Fault
12
3
456
Folding
12
34
6(erosion)7
1
23
4
1
2
34
5 1
2
34
5
6 12
3
4
5
6
5(tilting)
12
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Oldest- Siltstone
Youngest- Igneous Intrusion
13link
1
2
3
5
64
7
unconformity formation