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Inside the Earth
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Review of Density… Density is an expression of the relative heaviness of a substance
mass per unit volume
grams per cubic centimeter (g/cm3)
The density of pure water is 1g/cm3.
Granite rock is about 2.7 times denser at 2.7g/cm3.
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Formation of the Earth
• The most dense material (Iron and Nickel) settled to the core (center)
• Less dense matter (Silicates) formed the vast interior of the Earth (mantle).
• The least dense material (Granite and Basalt) formed the Earth’s solid stony crust.– Volcanic eruptions continued through the crust.
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Formation of the Earth Continued…
• With each eruption, gases, water vapor, ash and lava (molten material) were brought to the surface.
• The water vapor and gases formed the atmosphere.
• As the Earth cooled the water vapor turned to water and the rains started.
• The oceans formed from runoff. This also supplied the ocean with the mineral content it has today.
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IGNEOUS ROCKS
• Formed from molten material including volcanic lava, ash, or bombs as well as magma below Earth’s surface
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GRANITE BASALT
TYPES OF IGNEOUS ROCKS
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Composition (What it is made of)
• Crust
• Mantle
• Core
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Earth’s Layers
• How are the earth’s layers similar to an egg?
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The Crust
• Outer layer• 5-25 miles thick• Broken into pieces -
plates• 2 types of crust
– Oceanic • more dense – 2.9g/cm3
• made of basalt
– Continental • least dense – 2.8g/cm3
• made of granite
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Oceanic and Continental Crust
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The Mantle
• Middle layer• Very thick • Largest layer
Upper Mantle –
“Floats on plastic”
3.3 g/cm3
Plastic Mantle –
3.5 g/cm3
Lower Mantle –
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The Core
• Made mostly of iron• 1/3 of the earth’s mass• Very hot• The most dense• Divided into 2:
– The outer core • made up of liquid iron and nickel • density of 11.8g/cm3
– The inner core • made up of solid iron and nickel • density of 16.0g/cm3
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Physical Structure of the Earth• Crust (less than 1% of the total volume of the Earth)
– Continental Crust• 2.7 g/cm3
• granite– Oceanic Crust
• 2.9 g/cm3
• basalt
• Mantle (83% of the total volume of the Earth)– Lithosphere (lower crust and upper mantle)
• Plate in the “plate tectonic theory”• Floats on upper mantle like water• 3.1 g/cm3
– Asthenosphere • solid rock that flows slowly (like hot asphalt)• “Plastic” layer• 3.3 g/cm3
– Mesosphere• 4.5 g/cm3
• Core (16% of the total volume of the Earth)– Outer Core
• liquid iron and nickel• density of 11.8g/cm3
– Inner Core • Solid iron and nickel• density of 16.0g/cm3
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Continental Crust
Solid Mantle Solid Mantle
Plastic Mantle
Continental Crust
Ocean trench
Ocean
Oceanic crust
Subduction Zone
Plastic mantle = Asthenosphere
Solid mantle=Lithosphere
Label the following:
-Continental Crust-Ocean
-Oceanic Crust-Solid Mantle
-Plastic Mantle-Original Subduction
Zone-New Subduction
Zone
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Density Layering
• The overall density of the Earth is 5.5g/cm3
• The crust changes continually to balance the amount of lighter and denser material. – Erosion and glacial melting decreases
the density of the crust.– Volcanic eruption will increase the
density.
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Seismic waves• Evidence of distinct layers in the Earth with different
densities comes from the observations of seismic waves (the vibrations generated by earthquakes and explosions)
• As seismic waves move through the Earth, wave patterns may change indicating the waves were:– Reflected: bounced back due to extreme density– Refracted: directional change
• Measuring the changes in the velocity of these waves as they travel through the Earth provides information on the number of layers and the thickness and composition of the layers.
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