Plate Tectonics

Earth’s Interior

Convection and the Mantle

Drifting Continents

Sea-Floor Spreading

The Theory of Plate Tectonics

Table of Contents

Plate Tectonics - Earth’s Interior

Exploring Inside the Earth

Geologists have used two main types of evidence to learn about Earth’s interior: direct evidence from rock samples and indirect evidence from seismic waves.

Plate Tectonics

The Crust

The crust is a layer of solid rock that includes both dry land and the ocean floor.

- Earth’s Interior

Plate Tectonics

Plate Tectonics

The Mantle

Earth’s mantle is made up of rock that is very hot, but solid. Scientists divide the mantle into layers based on the physical characteristics of those layers.

- Earth’s Interior

Plate Tectonics

Temperature Inside the Earth

The graph shows how temperatures change between Earth’s surface and the bottom of the mantle. On this graph the temperature at the Earth’s surface is 0oC. Study the graph carefully and then answer the questions.

- Earth’s Interior

Plate Tectonics

Temperature Inside the Earth

The depth increases.

Reading Graphs:

As you move from left to right on the x-axis, how does depth inside the Earth change?

- Earth’s Interior

Plate Tectonics

Temperature Inside the Earth

About 1,600oC

Estimating:

What is the temperature at the boundary between the lithosphere and the asthenosphere?

- Earth’s Interior

Plate Tectonics

Temperature Inside the Earth

About 3,200oC

Estimating:

What is the temperature at the boundary between the lower mantle and the core?

- Earth’s Interior

Plate Tectonics

Temperature Inside the Earth

It generally increases with depth.

Interpreting Data:

How does temperature change with depth in Earth’s interior?

- Earth’s Interior

Plate Tectonics

The Core

The core is made mostly of the metals iron and nickel. It consists of two parts–a liquid outer core and a solid inner core.

- Earth’s Interior

Plate Tectonics

What You Know

What You Learned

Using Prior KnowledgeBefore you read, look at the section headings and visuals to see what this section is about. Then write what you know about Earth’s interior in a graphic organizer like the one below. As you read, write what you learn.

1. Earth’s crust is made of rock.2. Earth is very hot near the center.3. Dry land is part of the crust.4. The mantle is very hot.5. The core contains iron.

1. Geologists use seismic waves to study Earth’s interior.2. Radioactive substances heat the interior of Earth.3. The crust is thickest under high mountains.4. The mantle is solid.5. Movements in the outer core create Earth’s magnetic field.

- Earth’s Interior

Plate Tectonics

Links on the Structure of Earth

Click the SciLinks button for links on the structure of Earth.

- Earth’s Interior

Plate Tectonics

End of Section:

Earth’s Interior

Plate Tectonics

Types of Heat Transfer

There are three types of heat transfer: radiation, conduction, and convection.

- Convection and the Mantle

Plate Tectonics

Convection Currents

Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion.

- Convection and the Mantle

Plate Tectonics

Convection Currents in Earth

Heat from the core and the mantle itself causes convection currents in the mantle.

- Convection and the Mantle

Plate Tectonics

OutliningAn outline shows the relationship between major ideas and supporting ideas. As you read, make an outline about heat transfer. Use the red headings for the main topics and the blue headings for the subtopics.

Convection and the Mantle

I. Types of Heat TransferA. RadiationB. ConductionC. Convection

II. Convection CurrentsIII. Convection in Earth’s Mantle

- Convection and the Mantle

Plate Tectonics

More on Convection Currents in the Mantle

Click the PHSchool.com button for an activity about convection currents in the mantle.

- Convection and the Mantle

Plate Tectonics

Mantle Convection

Click the Video button to watch a movieabout mantle convections.

- Convection and the Mantle

Plate Tectonics

End of Section:

Convection and the Mantle

Plate Tectonics

Continental Drift

Wegener’s hypothesis was that all the continents were once joined together in a single landmass.

- Drifting Continents

Plate Tectonics

Evidence for Continental Drift

Fossils and rocks found on different continents provide evidence that Earth’s landmasses once were joined together in the supercontinent Pangaea.

- Drifting Continents

Plate Tectonics

Evidence for Continental Drift

Fossils and rocks found on different continents provide evidence that Earth’s landmasses once were joined together in the supercontinent Pangaea.

- Drifting Continents

Plate Tectonics

Identifying Supporting EvidenceAs you read, identify the evidence that supports the hypothesis of continental drift. Write the evidence in a graphic organizer like the one below.

Fossils

Climate change

Earth’s continents have moved.

Shape of continents

Evidence

Hypothesis

- Drifting Continents

Plate Tectonics

Links on Continental Drift

Click the SciLinks button for links on continental drift.

- Drifting Continents

Plate Tectonics

End of Section:Drifting

Continents

Plate Tectonics

Mid-Ocean Ridges

The East Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans.

- Sea-Floor Spreading

Plate Tectonics

What Is Sea-Floor Spreading?

In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

- Sea-Floor Spreading

Plate Tectonics

Evidence for Sea-Floor Spreading

Several types of evidence supported Hess’s theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

- Sea-Floor Spreading

Plate Tectonics

Subduction at Trenches

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle through deep-ocean trenches.

- Sea-Floor Spreading

Plate Tectonics

Growing an Ocean

Because of sea-floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.

- Sea-Floor Spreading

Plate Tectonics

SequencingMake a flowchart to show the process of sea-floor spreading.

Magma erupts along mid-ocean ridge.

Magma cools to form new sea floor.

Sea floor spreads away from ridge.

- Sea-Floor Spreading

Plate Tectonics

More on Sea-Floor Spreading

Click the PHSchool.com button for an activity aboutsea-floor spreading.

- Sea-Floor Spreading

Plate Tectonics

Sea-Floor Spreading

Click the Video button to watch a movieabout sea-floor spreading.

- Sea-Floor Spreading

Plate Tectonics

End of Section:Sea-Floor Spreading

Plate Tectonics

How Plates Move

The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates.

- The Theory of Plate Tectonics

Plate Tectonics

Plate Boundaries

- The Theory of Plate Tectonics

There are three kinds of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries. A different type of plate movement occurs along each type of boundary.

Plate Tectonics

Calculating a Rate

60,000,000 cm ÷ 10,000,000 years = 6 cm/yr

- The Theory of Plate Tectonics

To calculate the rate of plate motion, divide the distance the plate moves by the time it takes to move that distance.Rate = distance/timeFor example, a plate takes two million years to move 156 km. Calculate its rate of motion.156 km/2,000,000 years = 7.8 cm per yearPractice ProblemThe Pacific plate is sliding past the North American plate. It has take ten million years for the plate to move 600 km. What is the Pacific plate’s rate of motion?

Plate Tectonics

Continental Drift

It has taken the continents about 225 million years since the breakup of Pangaea to move to their present locations.

- The Theory of Plate Tectonics

Plate Tectonics

Continental Drift Activity

Click the Active Art button to open a browser window and access Active Art about continental drift.

- The Theory of Plate Tectonics

Plate Tectonics

Building VocabularyA definition states the meaning of a word or phrase by telling about its most important feature or function. After you read the section, reread the paragraphs that contain definitions of Key Terms. Use all the information you have learned to write a definition of each Key Term in your own words.

Key Terms: Examples:

- The Theory of Plate Tectonics

plate The lithosphere is broken into separate sections called plates.

scientific theory A scientific theory is a well-tested concept that explains a wide range of observations.

plate tectonics The theory of plate tectonics states that pieces of Earth’s lithosphere are in slow, constant motion, driven by convection currents in the mantle.

fault Faults are breaks in Earth’s crust where rocks have slipped past each other.

Key Terms: Examples:divergent boundary

rift valley

convergent boundary

transform boundary

The place where two plates move apart, or diverge, is called a divergent boundary.

A deep valley called a rift valley forms along the divergent boundary.

The place where two plates come together, or converge, is called a convergent boundary.

A transform boundary is a place where two plates slip past each other, moving in opposite directions.

Plate Tectonics

End of Section:The Theory of

Plate Tectonics

Plate Tectonics

Type of Plate Boundary

Type of Motion

Effect on Crust

Feature(s) Formed

Plates slide past each other.

Subduction or mountain building

Mid-ocean ridge, ocean floor

Graphic Organizer

Transform boundary

Crust is sheared. Strike-slip fault

Convergent boundary

Plates move together.

Mountains, volcanoes

Divergent boundary

Plates move apart.

Crust pulled apart by tension forces.

Plate Tectonics

End of Section:Graphic Organizer