Questions and Answers
What is relative dating?
Relative dating is determining whether an object or event is older or younger than other objects or events.
What is the principle of superposition?
A principle that states that younger rocks lie above older rocks in undisturbed sequences.
In a rock-layer sequence that hasn't been disturbed, older layers are found on top of younger layers.
False
What is a geologic column?
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How do geologists demonstrate an understanding of the geologic column?
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What do geologists assume about the way sediment is deposited to form rock layers?
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List and describe five events or features that can disturb rock-layer sequences.
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What is a fault in geology?
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What is an intrusion in geology?
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What is folding in geological terms?
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What is tilting in geology?
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What is an unconformity in geology?
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What are examples of features that can cut across rock layers?
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What creates a gap in geological columns?
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What two things can cause unconformity?
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What are the three categories of unconformities?
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How does a geologist recognize a disconformity?
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How are physical features used to determine relative ages?
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Study Notes
Relative Dating Overview
- Relative dating determines the chronological order of objects or events, identifying which is older or younger without specific numerical dates.
Superposition Principle
- Superposition states that in undeformed rock layers, younger rocks are positioned above older rocks, creating a vertical order.
Understanding Rock Layer Sequences
- Younger rock layers are always deposited on top of older ones, following the principle of superposition.
Geologic Column Definition
- A geologic column is an ideal representation of rock layers and fossils from oldest to youngest, providing a framework for understanding Earth's geological history.
Geologic Column Construction
- Geologists construct a geologic column using various rock sequences worldwide, identifying common layers to create a comprehensive view of Earth's stratigraphy.
Younger Features and Disturbances
- Features like faults that cut through rock layers are younger than the layers themselves, as the disturbance indicates prior layer formation.
Events Disturbing Rock Sequences
- Faults break the crust blocks sliding against each other.
- Intrusions occur when molten rock penetrates existing layers and cools.
- Folding bends rock layers due to internal Earth forces.
- Tilting slants rock layers without folding.
- Unconformity signifies missing geological time in a rock sequence.
Types of Geological Features
- Faults: breaks where crustal blocks move.
- Intrusion: molten rock that cools within pre-existing rock.
- Folding: rock layers bend under pressure.
- Tilting: slanting of rock layers due to internal forces.
- Unconformity: gaps indicating missing geological record.
Unconformities
- Disconformity: Missing section between parallel rock layers, often hard to detect as layers appear horizontal.
- Non-conformity: Sedimentary layers resting on eroded igneous or metamorphic rock.
- Angular Unconformity: Formed when tilted or folded layers are eroded before new horizontal layers are deposited on top.
Causes of Unconformities
- Non-Deposition occurs when sediment supply halts, leading to gaps when sedimentation resumes.
- Erosion happens when tectonic uplift exposes layers to weathering, resulting in gaps until deposition restarts.
Determining Relative Ages
- Geologists use physical features such as faults and intrusions to establish relative ages among rock layers, assessing the sequence and nature of disturbances.
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Description
This quiz covers the principles of relative dating in geology, including the superposition principle and the construction of the geologic column. Test your knowledge on how rock layers are categorized by age and the importance of understanding Earth's geological history.