dating rock layers and human impact
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Dating Rock Layers
How to tell how old the layers of rock are.
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What is Age?
There are two kinds:
-Absolute Age – The number of years since the rock formed. (150 million years old, 10 thousand years old.)
– Much harder to figure out. Often impossible.
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What is Age?
– Relative Age – The age compared to the ages of other rocks. (older than this rock, younger than that rock.)
– Much easier to figure out. Can be deduced from clues on the Earth.
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What are the ways to tell RELATIVE AGERELATIVE AGE.
1. Law of Superposition
2. Extrusion & Intrusion
3. Faults
4. Unconformities
5. Uniformitarianism
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What is the Law of Superposition?
In horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.
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Age and Superposition
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What is Extrusion?
• When magma cools on the surface of the Earth it’s called an EXTRUSION.
• Extrusions are always YOUNGER than the rock it is sitting on.
• For extrusion think exit or outside.
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What is an Intrusion?
• When magma cools beneath the surface of the Earth it’s called an INTRUSION.
• Intrusions are always YOUNGER than the rocks around it.
• For intrusion think inside.
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Here’s an Intrusion
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Extrusions? Intrusions?
First of all, which rock layer is the oldest?What is this called?
INTRUSION
EXTRUSIONF
G
C
D
A
B
E
More rock layers are deposited on top of the extrusion.
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What is a Fault?
• A BREAK in the Earth’s crust.
• A fault is always YOUNGER than the rock it cuts through.
• Faults move over time, making determining the age of the layers confusing.
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Here’s a Fault
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FaultsThis crack in the rock layers is called a fault.
Faults move over time causing the rock layers to move.
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Faults
As more time goes by, more rock layers are added on top. Making aging the rock layers difficult.
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Faults
A
A
B
B
C
C
DE
Geologists must then label each of the rock layers. This can be tough because they weren’t around to see the whole process occur.
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What is an Unconformity?
• The surface where new rock layers meet a much older rock surface beneath them.
• An unconformity shows where some rock layers have been lost because of erosion.
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Unconformity
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Uniformitarianism
• Geologic process that happened in the past can be explained by current geologic processes.
• Processes such as volcanism and erosion that go on today happened in a similar way in the past.
• Because geologic process tend to happen at a slow rate, this means that Earth must be very old.
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Summary
• Relative vs. Absolute Age• Determining Relative Age:
1. Law of Superposition – on top is younger
2. Intrusions – magma inside Earth.
3. Extrusions – magma on top of Earth.
4. Faults – breaks in the crust
5. Unconformities – signs of erosion.
6. Uniformitarianism – processes repeat and happen slowly showing extreme age of Earth.
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Human Impact
How humans have changed their geological and biological
environment.
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Human Impact
• Humans impact their environment in a number of different ways including the following:
1. Urbanization
2. Deforestation
3. Desertification
4. Changing Water Flow
5. Pollution
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What is Urbanization?
• The growth of urban areas (cities) caused by people moving into cities.
• When cities increase in size, the population of rural areas near the city may decrease.
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What is Deforestation?
• The removal of trees and other vegetation from an area.
• Urbanization can cause deforestation when forests are replaced with buildings.
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What is Desertification?
• The process by which land becomes more desert like and unable to support life.
• Urbanization can also lead to desertification.
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What happens when Water Flow is Changed?
• Digging irrigation canals to get water to crops changes the flow of rivers.
• Irrigation arid areas (deserts) changes the ecology of those areas.
• Building dams disrupts water flow and affects the ecology of the land and water.
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What is Pollution?
• Contamination of air, water or land by pollutants from human and natural sources.
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Summary
• Human Impact:1. Urbanization – building cities
2. Deforestation – cutting down trees
3. Desertification – turning land into deserts
4. Changing Water Flow – changes environment with increase or decrease of water
5. Pollution – contaminating environment