Plate Tectonics Section 1: Earth’s Interior Section 2: Convection and the Mantle Section 3: Drifting Continents Section 4: Sea-Floor Spreading Section.

Plate TectonicsPlate TectonicsSection 1: Earth’s InteriorSection 1: Earth’s Interior

Section 2: Convection and the MantleSection 2: Convection and the MantleSection 3: Drifting ContinentsSection 3: Drifting Continents

Section 4: Sea-Floor SpreadingSection 4: Sea-Floor SpreadingSection 5: The Theory of Plate TectonicsSection 5: The Theory of Plate Tectonics

Earth’s InteriorEarth’s Interior

How have geologists learned about How have geologists learned about Earth’s inner structure?Earth’s inner structure?• Geologists have used two main types of Geologists have used two main types of

evidence to learn about Earth’s interior:evidence to learn about Earth’s interior: Direct evidenceDirect evidence

• from from rock samplesrock samples Indirect evidenceIndirect evidence

• from from seismic wavesseismic waves


Geologists cannot Geologists cannot look inside Earthlook inside Earth• Use an indirect Use an indirect

method.method. Seismic Waves Seismic Waves

(Earthquake waves)(Earthquake waves)• Study how they Study how they

travel through travel through Earth.Earth.

Data reveals Data reveals several layersseveral layers



CrustCrust MantleMantle Outer CoreOuter Core Inner CoreInner Core


CrustCrust• Solid layer of rock that includes both dry land Solid layer of rock that includes both dry land

and the ocean floorand the ocean floor• Between 5 and 40 km thickBetween 5 and 40 km thick

Dry land Dry land • GraniteGranite

light in colorlight in color less denseless dense

Ocean floorOcean floor• BasaltBasalt

dark in colordark in color more densemore dense


MantleMantle• very hot, but solid rockvery hot, but solid rock• about 3,000 km thickabout 3,000 km thick

LithosphereLithosphere• Crust and Upper Mantle regionCrust and Upper Mantle region• ““Lithos”, Greek for StoneLithos”, Greek for Stone

AsthenosphereAsthenosphere• Remainder of MantleRemainder of Mantle• Very soft and hotter than LithosphereVery soft and hotter than Lithosphere• ““Asthenes”, Greek for WeakAsthenes”, Greek for Weak

*Lower Mantle*Lower Mantle• Solid and extends to the Core regionSolid and extends to the Core region



CoreCore• Mostly Iron and NickelMostly Iron and Nickel

Outer CoreOuter Core• molten metal (Fe and Ni) that surrounds the Inner molten metal (Fe and Ni) that surrounds the Inner

Core.Core.• Liquid Liquid

creates the magnetic field of the Earthcreates the magnetic field of the Earth Bar-magnet with North and South PolesBar-magnet with North and South Poles

Inner CoreInner Core• dense ball of metal (Fe and Ni)dense ball of metal (Fe and Ni)

Intense pressure prevents it from changing Intense pressure prevents it from changing from solid to liquid.from solid to liquid.


PressurePressure and and TemperatureTemperature increase increase as you move towards the center of as you move towards the center of the Earththe Earth


CoreCore

Earth’s Interior Earth’s Interior Assessment QuestionsAssessment Questions

Why is it difficult to determine Earth’s Why is it difficult to determine Earth’s inner structure?inner structure?

How are seismic waves used to provide How are seismic waves used to provide evidence about Earth’s interior?evidence about Earth’s interior?

List Earth’s three main layersList Earth’s three main layers What is the difference between the What is the difference between the

lithosphere and the asthenosphere? lithosphere and the asthenosphere? In which layer is each located?In which layer is each located?

Section 1.2 Section 1.2 Convection in the MantleConvection in the Mantle

How is heat transferred?How is heat transferred?• There are three types of heat transfer:There are three types of heat transfer:

RadiationRadiation ConductionConduction ConvectionConvection

RadiationRadiation

The transfer of energy through space.The transfer of energy through space.• No direct contact between a heat source and No direct contact between a heat source and

an object.an object. Sunlight warms the EarthSunlight warms the Earth

ConductionConduction

Heat transfer within a material or Heat transfer within a material or between materials that are touching.between materials that are touching.• Holding a hot spoon.Holding a hot spoon.

Conduction is responsible for some of the Conduction is responsible for some of the heat transfer inside Earth.heat transfer inside Earth.

ConvectionConvection

Heat transferred by the movements Heat transferred by the movements of liquids and gases.of liquids and gases.• Caused by:Caused by:

Density differencesDensity differences GravityGravity

• DensityDensity mass in a given volumemass in a given volume More heat = expansion = less denseMore heat = expansion = less dense Less heat = contraction = more denseLess heat = contraction = more dense


What causes convection currents?What causes convection currents?• GravityGravity• Difference in Density of liquids or gases.Difference in Density of liquids or gases.

Gravity pulls denser materials downwardGravity pulls denser materials downward

• More heat = expansion = less dense = moves More heat = expansion = less dense = moves upwardupward

• Less heat = contraction = more dense = moves Less heat = contraction = more dense = moves downwarddownward


Convection CurrentsConvection Currents

What causes convection currents in What causes convection currents in Earth’s mantle?Earth’s mantle?• Heat from the core and mantle causes Heat from the core and mantle causes

convection currents in the mantle.convection currents in the mantle.

Visual Summary of the Three Visual Summary of the Three Types of Heat TransferTypes of Heat Transfer

1.2 Assessment Questions1.2 Assessment Questions

1. How is heat transferred?1. How is heat transferred?

2. What causes convection currents?2. What causes convection currents?

3. What causes convection currents in 3. What causes convection currents in Earths mantle?Earths mantle?

4. What is conduction?4. What is conduction?


5. What is the role of gravity in 5. What is the role of gravity in creating convection currents?creating convection currents?

6. What part of Earth’s interior is like 6. What part of Earth’s interior is like the soup in the pot? What part is the soup in the pot? What part is like the burner on the stove? (Fig 9)like the burner on the stove? (Fig 9)

7. How is heat transferred through 7. How is heat transferred through space?space?

8. What is a convection current?8. What is a convection current?


9. In general, what happens to the density of 9. In general, what happens to the density of a fluid as it becomes hotter?a fluid as it becomes hotter?

10. Describe how convection currents form.10. Describe how convection currents form.11. Name two layers of Earth in which 11. Name two layers of Earth in which

convection currents take place.convection currents take place.12. What causes convection currents in the 12. What causes convection currents in the

mantle?mantle?13. What will happen to the convection 13. What will happen to the convection

currents in the mantle if Earth’s interior currents in the mantle if Earth’s interior eventually cools down? Explain.eventually cools down? Explain.

Section 1.3Section 1.3Drifting ContinentsDrifting Continents

What was Alfred Wegener’s What was Alfred Wegener’s hypothesis about the continents?hypothesis about the continents?

What evidence supported Wegener’s What evidence supported Wegener’s hypothesis?hypothesis?

Why was Wegener’s hypothesis Why was Wegener’s hypothesis rejected by most scientists of his rejected by most scientists of his day?day?

Continental DriftContinental Drift

Why do the coasts of several Why do the coasts of several continents match so neatly?continents match so neatly?• West Africa and Eastern South America West Africa and Eastern South America

seem to fit together like puzzle pieces.seem to fit together like puzzle pieces.

Continental DriftContinental Drift

Alfred Wegener Alfred Wegener • Hypothesized that Hypothesized that

Earth’s continents Earth’s continents has moved over has moved over time.time.

All part of one large, All part of one large, ancient landmass ancient landmass

Drifted apart over Drifted apart over timetime

• His idea was called His idea was called “Continental Drift”“Continental Drift”

PangaeaPangaea

Ancient landmassAncient landmass• ““All Lands”All Lands”• All continents connected togetherAll continents connected together

300 million years ago300 million years ago

PangaeaPangaea

Slowly broke apart Slowly broke apart to where to where continents are continents are located today.located today.• Supported by Supported by

studying:studying: land featuresland features fossilsfossils evidence of climate evidence of climate

changechange

PangaeaPangaea

Supporting EvidenceSupporting Evidence• Land FeaturesLand Features

mountain ranges on Africa and South mountain ranges on Africa and South America lined-up.America lined-up.

coal fields in Europe and North America coal fields in Europe and North America match-upmatch-up

Supporting Pangaea: Supporting Pangaea: Land FeaturesLand Features

PangaeaPangaea

Supporting EvidenceSupporting Evidence• FossilsFossils

GlossopterisGlossopteris• fernlike plantfernlike plant

Mesosaurus and LystrosaurusMesosaurus and Lystrosaurus• land-dwelling dinosaursland-dwelling dinosaurs

Fossils of these organisms are found on many Fossils of these organisms are found on many different continents separated by great different continents separated by great oceans!!oceans!!

How could that be possible?How could that be possible?

Supporting Pangaea: FossilsSupporting Pangaea: Fossils

PangaeaPangaea ClimateClimate

• SpitsbergenSpitsbergen Present location: Arctic Ocean (Cold!!)Present location: Arctic Ocean (Cold!!)

• TropicalTropical plant fossils are found there! plant fossils are found there!

• South AfricaSouth Africa Present climate: Mild/WarmPresent climate: Mild/Warm

• Deep scratches, caused by glaciers are found in Deep scratches, caused by glaciers are found in the crust.the crust.

• Glaciers exist in very cold environments!!Glaciers exist in very cold environments!!

*Climates changed because landmasses *Climates changed because landmasses moved.moved.

Hypothesis Rejected!!Hypothesis Rejected!!

Wegener was not able to provide a Wegener was not able to provide a satisfactory explanation for the force satisfactory explanation for the force that pushes or pulls the continents.that pushes or pulls the continents.• More evidence would be needed.More evidence would be needed.

Mountain FormationMountain Formation

Wegener hypothesized that when Wegener hypothesized that when continents collide, their edges continents collide, their edges crumple and fold.crumple and fold.• Huge mountains form.Huge mountains form.


1. What was Alfred Wegener’s hypothesis 1. What was Alfred Wegener’s hypothesis about the continents?about the continents?

2. What evidence supported Wegener’s 2. What evidence supported Wegener’s hypothesis?hypothesis?

3. Why was Wegener’s hypothesis 3. Why was Wegener’s hypothesis rejected by most scientists of his day?rejected by most scientists of his day?


4. What do the matching mountain ranges 4. What do the matching mountain ranges in Africa and South America show, in Africa and South America show, according to Wegener’s hypothesis?according to Wegener’s hypothesis?

5. How would continental drift affect the 5. How would continental drift affect the continent’s climate?continent’s climate?

6. According to Wegener, how do 6. According to Wegener, how do mountains form?mountains form?

1.3 Assessment Questions1.3 Assessment Questions 7. Who proposed the concept of 7. Who proposed the concept of

continental drift?continental drift? 8. According to the hypothesis of 8. According to the hypothesis of

continental drift, how would a world map continental drift, how would a world map have changed over the last 250 million have changed over the last 250 million years?years?

9. What evidence supported the 9. What evidence supported the hypothesis of continental drift?hypothesis of continental drift?

10. How did fossils provide evidence for 10. How did fossils provide evidence for continental drift?continental drift?


11. Deposits of coal have been found 11. Deposits of coal have been found beneath the ice of Antarctica. But coal beneath the ice of Antarctica. But coal only forms in warm swamps. Use only forms in warm swamps. Use Wegener’s hypothesis to explain how coal Wegener’s hypothesis to explain how coal could be found so near to the South Pole.could be found so near to the South Pole.

12. Why did most scientists reject 12. Why did most scientists reject Wegener’s hypothesis of continental drift?Wegener’s hypothesis of continental drift?

13. Do you think the scientists of 13. Do you think the scientists of Wegener’s time should have accepted his Wegener’s time should have accepted his hypothesis? Why or why not?hypothesis? Why or why not?

Chapter 1.4 Chapter 1.4 Sea-Floor SpreadingSea-Floor Spreading

Mid-Ocean RidgesMid-Ocean Ridges• an undersea maintain chain where new an undersea maintain chain where new

ocean floor is produced.ocean floor is produced. divergent (moving apart) plate boundarydivergent (moving apart) plate boundary


What device is used to map the What device is used to map the ocean floor?ocean floor?

• Mapped in the mid-1900’s by using Mapped in the mid-1900’s by using SONARSONAR..

Underwater soundwavesUnderwater soundwaves• How long does the echo take to travel? = distance How long does the echo take to travel? = distance

to the bottom.to the bottom.

Mid-Ocean RidgeMid-Ocean Ridge


What is the process of Sea-Floor What is the process of Sea-Floor Spreading?Spreading?

• Sea floor spreads apart along both sides Sea floor spreads apart along both sides of a mid-ocean ridge as new crust is of a mid-ocean ridge as new crust is added from below.added from below.

Evidence of Sea-Floor SpreadingEvidence of Sea-Floor Spreading

What is the evidence of Sea-Floor What is the evidence of Sea-Floor Spreading?Spreading?• 1. 1. Molten MaterialMolten Material

Bubble-shaped rocks found on the ocean Bubble-shaped rocks found on the ocean floor.floor.

• caused only by cooling magmacaused only by cooling magma


• 2. 2. Magnetic StripesMagnetic Stripes Iron in molten rock aligns to magnetic polesIron in molten rock aligns to magnetic poles Poles “Flip” over many thousands of yearsPoles “Flip” over many thousands of years

• Repeated pattern of north and south orientation.Repeated pattern of north and south orientation. pattern is the same on both sides of the Mid-pattern is the same on both sides of the Mid-

Ocean Ridge.Ocean Ridge.

Magnetic Reversal StripesMagnetic Reversal Stripes


• 3. Drilling Samples3. Drilling Samples Oldest rocks Oldest rocks

• farther from Mid-Ocean farther from Mid-Ocean RidgeRidge

Youngest rocksYoungest rocks• closer to Mid-Ocean Ridgecloser to Mid-Ocean Ridge

Subduction at TrenchesSubduction at Trenches

What happens at Deep-Ocean What happens at Deep-Ocean Trenches?Trenches?

• TrenchesTrenches Opposite of Sea-Floor SpreadingOpposite of Sea-Floor Spreading

• Oceanic rock is forced downward, or subducts, Oceanic rock is forced downward, or subducts, and eventually melts into magma.and eventually melts into magma.

Deep Ocean TrenchesDeep Ocean Trenches

Subduction at TrenchesSubduction at Trenches

• Together, Subduction and Sea-Floor Together, Subduction and Sea-Floor Spreading act as a conveyor beltSpreading act as a conveyor belt

cooling magma into new rock (Mid-Ocean cooling magma into new rock (Mid-Ocean Ridges).Ridges).

melting old rock into magma (Trenches)melting old rock into magma (Trenches)


1.Along what feature of the ocean floor1.Along what feature of the ocean floordoes sea-floor spreading begin?does sea-floor spreading begin?

2.What are the steps in the process of sea-floor 2.What are the steps in the process of sea-floor spreading?spreading?

3.What three types of evidence provided support for 3.What three types of evidence provided support for the theory of sea-floor spreading?the theory of sea-floor spreading?

4.How do rocks along the central valley of the mid-4.How do rocks along the central valley of the mid-ocean ridge provide evidence of sea-floor ocean ridge provide evidence of sea-floor spreading?spreading?


5.Where would you expect to find the oldest rock on 5.Where would you expect to find the oldest rock on the ocean floor?the ocean floor?

6.What is a deep-ocean trench?6.What is a deep-ocean trench?

7.What happens to oceanic crust at a deep–ocean 7.What happens to oceanic crust at a deep–ocean trench?trench?

Plate Tectonics Section 1: Earth’s Interior Section 2: Convection and the Mantle Section 3: Drifting Continents Section 4: Sea-Floor Spreading Section.

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