relative time:
DESCRIPTION
Relative Time:. Ages of events are placed in order of occurrence. No exact date is identified. Ex. WWI and WWII I am the second child in my family. Absolute Time:. identifies the exact date of an event. Ex. 65 Million Years Ago 1990. Finding age with relative time:. - PowerPoint PPT PresentationTRANSCRIPT
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Relative Time:
Ages of events are placed in order of occurrence.
No exact date is identified. Ex. WWI and WWII I am the second child in my family.
![Page 2: Relative Time:](https://reader035.vdocuments.mx/reader035/viewer/2022062719/56813066550346895d964024/html5/thumbnails/2.jpg)
Absolute Time:
identifies the exact date of an event. Ex. 65 Million Years Ago 1990
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Finding age with relative time:1. The Law of Superposition - in a
sequence of undisturbed sedimentary rocks, the oldest rocks will be at the bottom.
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2. The law of cross-cutting relationships – anything that cuts across layers of rock is younger than the rocks that it has intruded into. This applies to faults and igneous intrusions.
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3. The law of included fragments - the fragments that make up a rock are older than the entire sample.
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4. The Law of Folds or Tilts: tilts in rocks are younger than the rocks themselves.
5. Original Horizontality- Rocks are usually deposited flat and level.
6. Cole’s Law-
Thinly sliced cabbage.
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Other Guidelines for figuring out a sequence:
Sedimentary rocks are usually formed under water.
Weathering and erosion usually happen above water (on dry land).
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Contact metamorphism shows that the rock that was changed was there first when the intrusion happened.
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Time for a worksheet
Sequence 1 & 2
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Sequence 1: Uplift & Erosion
1. Limestone deposited
2. Sandstone deposited
3. Shale Deposited
4. Uplift
5. Erosion
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Sequence 2: Faulting
1. Limestone deposited
2. Sandstone deposited
3. Shale deposited
4. Faulting
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Time for another worksheet
Sequence 3 & 4
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Sequence 3: Folding
1. Limestone deposited
2. Sandstone deposited
3. Shale deposited
4. Folding
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By the way…
How can you tell if folding has gone so far as to flip the layers over?
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Sequence 4: Igneous Intrusion
1. Limestone deposited
2. Sandstone deposited
3. Shale deposited4. Igneous Intrusion
Note: contact metamorphism is the same event as the intrusion.
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Formation of an unconformity
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Layers are formed according to superposition.
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Something happens to uplift the areafoldingfaulting, etc.
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Erosion wears away the uppermost layers
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Area submerges and deposition begins again.
Here’s the unconformity