Plate Tectonics Ch 4

Earth’s Interior Section 1

Layers of the Earth Section 2

Drifting Continents Section 3 Plate Boundaries Section 4

The Theory of Plate Tectonics Section 5

Section 1: Earth’s Interior• We know about the earth’s interior from

indirect evidence– Example of indirect evidence: How would you

know where to hang a picture so that it stays hung solidly? You can’t see inside the wall.

• Temperature and pressure change as you go deeper towards the core – Temperature increases towards the center of the

earth– Pressure also increases towards the center

Cross-section of earth’s interior showing crust, mantle and the two parts of the core

Four Main Layers of the Earth’s Interior

• The crust – the layer of rock that forms the earth’s outer skin, includes rocks, mountains, soil and water

• The mantle – 5-40 km down. Rock is of hotter temperatures. About 3,000 km thick

• The outer core – liquid molten iron metal• inner core – solid iron metal due to high

pressure

This slide shows how temperature increases towards the center of the earth, as well as some

of the elements found in each layer.

Seismic waves are a window to the interior of the earth. S-wavesdo not travel through liquids. A shadow zone occurs on the opposite side of the earth from where the earth-quake occurred.All seismicstations in the shadow zone would record P-wavesbut not S-waves.

Earth’s Magnetic Field

Currents in the liquid outer core force the solid inner core to spin at a slightly faster rate than the rest of the planet.

These currents in the outer core create the magnetic field causing the earth to act like a giant bar magnet.

The magnetic field protects living things from dangerous solar radiation.

Section 2: Convection Currents and the Mantle

• In the upper-most part of the Mantle is a rigid layer called the lithosphere. Litho means rocky or stone.

• Below the lithosphere is the asthenosphere, which means weak, but it is actually semi-molten and the semi-melted rock is moving in

slow currents!• The lithosphere rides on top of the slow moving

asthensphere.

ConvectionConvection is heat transfer by movement of

heated fluid (gas or liquid). Heat transfer by convection is caused by

differences of temperature and density within that fluid (for example, how this room is heated)

The heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity all combine to set convection going in the earth’s mantle.

This slide shows the convection currents found in the asthenosphere.

(Note the drawing is not drawn to scale)

These convection cells move sections of the crust. Hot, less dense molten lava rises to the

surface creating new crustal sections. Old crust is “subducted” or forced down in the

earth, melting and recycling!

Section 3: Drifting Continents

• 1910 Alfred Wegener hypothesized that all the continents had once been joined together in a single landmass and have since drifted apart.

• Evidence includes mountain ranges that line up, fossils that were similar, mineral deposits that also lined up, as well as climate evidence and traces

• Most scientists at the time did not believe in this theory of drifting continents, as Wegener could not explain what force was actually moving the continents.

Section 4: Sea-Floor Spreading

• Mapping the Mid-Ocean Ridge – the longest chain of mountains in the world! (and they are underwater)

• Sonar mapping(begun in 1959) revealed the location of these Mountains

Evidence of Sea-Floor Spreading• Ocean floors move

like conveyor belt, carrying the continents along with them.

• At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge.

This little animation shows molten lava coming to the surface at the mid-oceanic ridge. As it reaches the surface, the lava cools, hardens and is pushed aside by new magma coming to the surface.

• Molten material found erupting along mid-ocean ridge

• Iron within basaltic crust magnetized.

• Strips on either side of the mid-ocean ridge that match up

Sea-Floor SpreadingReview of Evidence

Subduction at Deep-Ocean Trenches

Trenches – forms where the oceanic crust is thrust back down into the mantle and begins cracking and melting

Crust and Lithosphere being thrust down at subduction zones.

Notice the melting of the plate, forming the pockets of hot magma

Section 5: The Theory of Plate Tectonics

• The Theory of Plate Tectonics explains the formation, movement, and subduction of Earth’s plates.

• There are three types of plate boundaries: convergent, divergent, and transform.

• Plate converge in three different way: Two ocean crusts colliding, two continental crusts colliding, and a continental crust colliding with an ocean crust.

Location of earthquakes and volcanoes found along convergent and divergent plate boundaries

(and over hot spots such as Hawaii and Yellowstone)

Ring of Fire

Plates of the Earth

Plate Boundaries Transform, Divergent, Convergent

Convergent Plate Boundaries

Ocean crust | Ocean crust (Japan, Taiwan)

Ocean crust | Continent crust (Andes Mts.)

Continent crust | Continent crust (Himalaya Mts.)

Two plates “coming together”

Folded Mountain Belts occur when continents are involved

(similar to “rug” analogy)

Divergent Plate Boundaries

Plates are created and move apart at the mid-oceanic mountain range in the Atlantic Ocean

Two plates “moving apart”

Transform Faults

Two plates “slide” past each other.

San Andreas Fault in Southern California

San Andreas Fault in California (transform fault)

Locate: Trench, folded mountain belts, mid-oceanic ridge, volcanoes, hot spots, crust, subduction zones, transform fault, lithosphere, convergent plate boundary, divergent plate boundary, asthenosphere

Review of Terms

Motion of

India’s plate

The formation of a rift valley

Convergent Boundary

Can you identify and describe each type of convergent plate

boundary?

How islands are formed: Hot spots in the crust allow melted magma to form little cones on the ocean floor

that build higher and higher to create islands.

Earthquakes

What is happening to the Red Sea?

Will we need to someday rename Lake Victoria to Victoria Ocean?

Folded Mountain Belts