Inside the Earth

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.

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.

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.

IGNEOUS ROCKS

• Formed from molten material including volcanic lava, ash, or bombs as well as magma below Earth’s surface

GRANITE BASALT

TYPES OF IGNEOUS ROCKS

Composition (What it is made of)

• Crust

• Mantle

• Core

Earth’s Layers

• How are the earth’s layers similar to an egg?

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

Oceanic and Continental Crust

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 –

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

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

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

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.

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.