• What is the theory of plate tectonics?

• What are the three types of plate boundaries?

• Why do tectonic plates move?

The Theory of Plate Tectonics

• Lesson 3 Reading Guide - Vocab

• plate tectonics

• lithosphere

• divergent plate boundary

• transform plate boundary

• convergent plate boundary

The Theory of Plate Tectonics

• subduction

• convection

• ridge push

• slab pull

The Plate Tectonics Theory (cont.)

What is plate tectonics?

• The theory of plate tectonics, proposed in the late 1960s, states that Earth’s surface is made of rigid slabs of rock, or plates, that move with respect to each other.

• Plate tectonics suggests that Earth’s surface is divided into large plates of rigid rock and each plate moves over Earth’s hot and semiplastic mantle.

The Plate Tectonics Theory

• Geologists use the word tectonic to describe the forces that shape Earth’s surface and the rock structures that form as a result.

• The cold and rigid outermost rock layer of the Earth is called the lithosphere.

• The lithosphere is made up of the crust and the solid, uppermost mantle.

The Plate Tectonics Theory (cont.)

• The lithosphere is thin below mid-ocean ridges and thick below continents.

• Earth’s tectonic plates are large pieces of the lithosphere that fit together like the pieces of a giant jigsaw puzzle.

• The layer of Earth below the lithosphere, called the asthenosphere, is so hot that it behaves like a plastic material and enables Earth’s plates to move.

The Plate Tectonics Theory (cont.)

Earth’s Tectonic Plates

• Continental Drift Movie Activity

• Read HANDOUT

Plate Boundaries (cont.)

What are the three types of plate boundaries?

• A divergent plate boundary forms where two plates separate.

• When the seafloor spreads at a mid-ocean ridge, lava erupts, cools, and forms new oceanic crust.

• Divergent plate boundaries can also exist in the middle of a continent, where they pull continents apart and form rift valleys.

Plate Boundaries

• Lesson 3-3

• A transform plate boundary forms where two plates slide past each other.

• As they move past one another, the plates can get stuck and stop moving.

• Stress builds up where the plates are stuck until they eventually break and suddenly move apart, resulting in a rapid release of energy as earthquakes.

Plate Boundaries (cont.)

• Lesson 3-3

• Convergent plate boundaries form where two plates collide.

• The denser plate sinks below the more buoyant plate in a process called subduction.

• The area where a denser plate descends into Earth along a convergent plate boundary is called a subduction zone.

Plate Boundaries (cont.)

Plate Boundaries (cont.)

subductionfrom Latin subductus, means “to lead under, removal”

• When an oceanic plate and a continental plate collide, the denser oceanic plate subducts under the edge of the continent, creating a deep ocean trench and a line of volcanoes above the subducting plate on the edge of the continent.

Plate Boundaries (cont.)

• Lesson 3-3

• When two continental plates collide, neither plate is subducted, and mountains form from uplifted rock.

Plate Boundaries (cont.)

• Lesson 3-3

• Creating the 3 plate boundaries

• Foldables Activity

• Scientists can measure how fast continents move using a network of satellites called the Global Positioning System.

• Because plates are rigid, tectonic activity occurs where plates meet.

Evidence for Plate Tectonics

Evidence for Plate Tectonics (cont.)

How are earthquakes and volcanoes related to the theory of plate tectonics?

• Volcanoes form where plates separate along a mid-ocean ridge or continental rift or collide along a subduction zone.

• Mountains can form where two continents collide.

Evidence for Plate Tectonics (cont.)

Notice the relationship between earthquake epicenters, volcanoes, and plate boundaries.

Plate Motion (cont.)

What causes convection?

• Earth’s plates move because the asthenosphere moves underneath the lithosphere.

• Convection is the circulation of material caused by differences in density.

• Hot mantle material rises upward and comes in contact with Earth’s crust.

Plate Motion

• As the mantle cools, it becomes denser and then sinks, forming a convection current.

• Convection currents in the asthenosphere act like a conveyor belt moving the lithosphere above it.

• There are three forces that interact to cause plate motion: basal drag, ridge push, and slab pull.

Plate Motion (cont.)

• Basal drag refers to how convection currents in the asthenosphere circulate and drag the lithosphere like a conveyor belt.

• Rising mantle material at mid-ocean ridges creates the potential for plates to move away from the ridge with a force called ridge push.

Plate Motion (cont.)

• Lesson 3-4As a slab, or dense plate, sinks, it pulls on the rest of the plate with a force called slab pull.

• Plate tectonics has become the unifying theory of geology, but several unanswered questions remain.

• Why is Earth the only planet in the solar system that has plate tectonic activity?

• Why do some earthquakes and volcanoes occur far away from plate boundaries?

A Theory in Progress

• What forces dominate plate motion?

• What will scientists study next? This is a 3-D image of seismic wave velocities from a new technique called anisotropy.

• Lesson 3 - VS

• Tectonic plates are made of cold and rigid slabs of rock.

• Mantle convection—the circulation of mantle material due to density differences—drives plate motion.

• Lesson 3 - VS

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

• Lesson 3 – LR1

A. semiplastic

B. lithosphere

C. tectonic

D. mantle

What word do geologists use to describe the forces that shape Earth’s surface?

• Lesson 3 – LR2

A. seafloor

B. lithosphere

C. biosphere

D. hydrosphere

Which of these is made up of the crust and the solid, uppermost mantle?

• Lesson 3 – LR3

A. convergent plate boundary

B. transform plate boundary

C. new plate boundary

D. divergent plate boundary

What type of boundary forms where two plates separate?

• Lesson 3 - Now

5. Continents drift across a molten mantle.

6. Mountain ranges can form when continents collide.

Do you agree or disagree?

• Chapter Review Menu

Key Concept Summary

Interactive Concept Map

Chapter Review

Standardized Test Practice

• The BIG Idea

The theory of plate tectonics states that Earth’s lithosphere is broken up into rigid plates that move over Earth’s surface.

• Key Concepts 1

• The puzzle piece fit of continents, fossil evidence, climate, rocks, and mountain ranges supports the hypothesis of continental drift.

• Scientists were skeptical of continental drift because Wegener could not explain the mechanism for movement.

Lesson 1: The Continental Drift Hypothesis

• Key Concepts 2Lesson 2: Development of a Theory

• Seafloor spreading provides a mechanism for continental drift.

• Seafloor spreading occurs at mid-ocean ridges.• Evidence of magnetic reversal in rock, thermal energy trends, and the discovery of seafloor spreading all contributed to the development of the theory of plate tectonics.

• Key Concepts 3

• Types of plate boundaries, the location of earthquakes, volcanoes, and mountain ranges, and satellite measurement of plate motion support the theory of plate tectonics.

• Mantle convection, ridge push, and slab pull are the forces that cause plate motion. Radioactivity in the mantle and thermal energy from the core produce the energy for convection.

Lesson 3: The Theory of Plate Tectonics

• Chapter Review – MC1

A. animalsB. ice sheetsC. plant fossils D. plate boundaries

Which of these have been found on several continents separated by oceans, suggesting that they were once geographically closer together?

• Chapter Review – MC2

A. continental driftB. plate tectonicsC. seafloor spreadingD. magnetic reversal

Which of these refers to the process by which new oceanic crust forms along a mid-ocean ridge as older oceanic crust moves away from the ridge?

• Chapter Review – MC3

A. mantleB. lithosphereC. plateD. transform plate boundary

What is the rigid outermost layer of Earth called?

• Chapter Review – MC4

A. transform plate boundaryB. divergent plate boundaryC. convergent plate boundaryD. semiplastic mantle

What forms where two plates slide past each other?

• Chapter Review – MC5

A. seafloor spreadingB. convergenceC. convectionD. subduction

What is the process in which a denser plate sinks below a more buoyant plate?

• Chapter Review – STP1

A. WegenerB. PangaeaC. mantleD. seafloor

What is the name of the supercontinent that all continents were once part of?

• Chapter Review – STP2

A. AntarcticaB. plate boundariesC. mountain rangesD. Africa

Where did scientists find glacial features that are usually associated with cooler climates?

• Chapter Review – STP3

A. volcanoesB. oceanic crustC. pillow lavaD. mid-ocean ridges

Which term refers to vast mountain ranges on the seafloor?

• Chapter Review – STP4

A. the theory of plate tectonicsB. the theory of mid-ocean ridgesC. the theory of divergent plate

boundariesD. the theory of transform plate

boundaries

Which of these states that Earth’s surface is made of rigid slabs of rock that move with respect to one another?

• Chapter Review – STP5

A. ridge pushB. basal dragC. slab pullD. plate tectonics

What is the name for the force that pulls on the rest of a plate as part of a dense plate sinks?