# Chapter 1 Plate Tectonics

Chapter 1 focuses on Plate Tectonics, looking at the Earth's layers, Earth's evolution, and plate movement.

Lessons included in this chapter:

#1 The Earth's Layers

#2 Pangea to Present

#3 How Earth's Plates Move

Resources for Teachers can be found under the Chapter #1 Copymaster.

Select from the options on the right to proceed.

# The Earth's Layers Lesson #1

The Four Layers

The Earth is composed of four different layers. Many geologists believe that as the Earth cooled the heavier, denser materials sank to the center and the lighter materials rose to the top. Because of this, the crust is made of the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).

The crust is the layer that you live on, and it is the most widely studied and understood. The mantle is much hotter and has the ability to flow. The Outer and Inner Cores are hotter still with pressures so great that you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!!!!!!

The Crust

The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans(oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust). The temperatures of the crust vary from air temperature on top to about 1600 degrees Fahrenheit (870 degrees Celcius) in the deepest parts of the crust. You can bake a loaf of bread in your oven at 350 degrees Fahrenheit , at 1600 degrees F. rocks begin to melt.

The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, plastic mantle which is located below the crust. These plates usually move along smoothly but sometimes they stick and build up pressure. The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result!

Notice how thin the crust of the Earth is in comparison to the other layers. The seven continents and ocean plates basically float across the mantle which is composed of much hotter and denser material.

The crust is composed of two basic rock types granite and basalt. The continental crust is composed mostly of granite. The oceanic crust consists of a volcanic lava rock called basalt.

Basaltic rocks of the ocean plates are much denser and heavier than the granitic rock of the continental plates. Because of this the continents ride on the denser oceanic plates. The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere. The layer below the rigid lithosphere is a zone of asphalt-like consistancy called the Asthenosphere. The asthenosphere is the part of the mantle that flows and moves the plates of the Earth.

The Mantle

The mantle is the layer located directly under the sima. It is the largest layer of the Earth, 1800 miles thick. The mantle is composed of very hot, dense rock. This layer of rock even flows like asphalt under a heavy weight. This flow is due to great temperature differences from the bottom to the top of the mantle. The movement of the mantle is the reason that the plates of the Earth move! The temperature of the mantle varies from 1600 degrees Fahrenheit at the top to about 4000 degrees Fahrenheit near the bottom!

Convection Currents

The mantle is made of much denser, thicker material, because of this the plates "float" on it like oil floats on water.

Many geologists believe that the mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over. The next time you heat anything like soup or pudding in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the mantle they also move the crust. The crust gets a free ride with these currents. A conveyor belt in a factory moves boxes like the convection currents in the mantle moves the plates of the Earth.

Outer Core

The core of the Earth is like a ball of very hot metals. (4000 degrees F. to 9000 degrees F.) The outer core is so hot that the metals in it are all in the liquid state. The outer core is located about 1800 milesbeneath the crust and is about 1400 miles thick. The outer core is composed of the melted metals nickel and iron.

Inner Core

The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place as a solid. The inner core begins about 4000 miles beneath the crust and is about 800 miles thick. The temperatures may reach 9000 dgrees F. and the pressures are 45,000,000 pounds per square inch. This is 3,000,000 times the air pressure on you at sea level!!!

Answer the following questions on a sheet of paper with your partner. If you need to look back to find the answers use the page titles located directly under the questions to help you. When you finish the questions click on the Earth icon to return the program to the beginning.

1. Name the four layers of the Earth in order from the outside to the center of the Earth.

2. What causes the mantle to "flow"?

3. What are the two main metals that make up the outer and inner core?

4. Describe in your own words how the Earth's layers were formed. "The Four Layers" will help you.

# Pangaea to the Present Lesson #2

The Earth is a dynamic or constantly changing planet. The thin, fragile plates slide very slowly on the mantle's upper layer. This sliding of the plates is caused by the mantle's convection currents slowly turning over and over. This overturn is like a conveyor belt that moves the plates of the crust.

These plates are in constant motion causing earthquakes, mountain building, volcanism, the production of "new" crust and the destruction of "old" crust. The following cards will teach you more about the Earth's plates.

The Earth's crust is broken into many pieces. These pieces are called plates. There are twelve main plates on the Earth's surface. The red lines on this map of the world represent the largest plate boundaries. A plate boundary occurs where two plates come together. There are three kinds of plate boundaries:

1. Convergent boundary -where two plates collide to form mountains or a subduction zone.

2. Divergent boundary -where two plates are moving in opposite directions as in a mid-ocean ridge.

3. Transform boundary -where two plates are sliding past each other as in the San Andreas fault of California.

The Earth's plates are in constant, but very, very slow motion. They move at only 1/2 to 4 inches (1.3 to 10 centimeters) per year!! This does not seem like much, but over millions of years it adds up to great distances of movement.

The Continental Drift Theory states that the continents have moved and are still moving today. In 1912 Alfred Wegener introduced this theory, but he did not fully understand what caused the plates to move. A theory is an explanation of a scientific process that has been successfully tested by many different methods.

The motion of the Earth's plates help scientists to understand why earthquakes, volcanoes, and mountain building occur.

You will learn more about why the plates are moving in the next lesson, "How Plates Move".

Scientists believe these plates have been moving for millions of years. In fact, 250 millions years ago the Earth's seven continents were all grouped together into a supercontinent called Pangea.

Just before the days of the dinosaurs the Earth's continents were all connected into one huge landmass called Pangaea . This huge supercontinent was surrounded by one gigantic ocean called Panthalassa.

Notice the postion of the continents of Antarctica (Far north of its current position), Australia (flipped sideways and far west of its current position) and the subcontinent of India (Hundreds of miles from Asia).

Scientists believe that the North American continent was located much farther south and east of it's position today. In fact, much of North America was in or near the tropics!! How do scientists know this?? They have found fossils from this period of time. These fossils are of tropical plants and animals. The fossils have been found in cold regions like North Dakota and Greenland!!!

180 Million Years Ago

About 180 million years ago the supercontinent Pangea began to break up. Scientists believe that Pangea broke apart for the same reason that the plates are moving today. The movement is caused by the convection currents that roll over in the upper zone of the mantle. This movement in the mantle causes the plates to move slowly across the surface of the Earth. About 200 million years ago Pangaea broke into two new continents Laurasia and Gondwanaland. Laurasia was made of the present day continents of North America (Greenland), Europe, and Asia. Gondwanaland was made of the present day continents of Antarctica, Australia, South America. The subcontinent of India was also part of Gondwanaland. Notice that at this time India was not connected to Asia. The huge ocean of Panthalassa remained but the Atlantic Ocean was going to be born soon with the splitting of North America from the Eurasian Plate.

How do we know that South America was attached to Africa and not to North America 180 million years ago?

Scientists today can read the history of the rock record by studying the age and mineral content of the rocks in a certain area.

The Triple Junction was formed because of a three-way split in the crust allowing massive lava flows. The split was caused by an upwelling of magma that broke the crust in three directions and poured out lava over hundreds of square miles of Africa and South America.

The rocks of the triple junction, which today is the west central portion of Africa and the east central portion of South America, are identical matches for age and mineral make up. In other words the rocks in these areas of the two continents were produced at the same time and in the same place. This tells us that South America and Africa were connected at one time!

Today these two continents are separated by the Atlantic Ocean which is over 2000 miles wide!

135 Million Years Ago

About 135 million years ago Laurasia was still moving, and as it moved it broke up into the continents of North America, Europe and Asia (Eurasian plate). Gondwanaland also continued to spread apart and it broke up into the continents of Africa, Antarctica, Australia, South America, and the subcontinent of India. Arabia started to separate from Africa as the Red Sea opened up.

The red arrows indicate the direction of the continental movements. Notice how far the Indian subcontinent has to move to get to its present postion connected to Asia.

The Atlantic, Indian, Arctic, and Pacific Oceans are all beginning to take shape as the continents move toward their present positions.

The plates are still moving today making the Atlantic Ocean larger and the Pacific Ocean smaller. The yellow arrows on the world map indicate the direction of plates movements today.

Notice the position of the Indian Subcontinent today. It moved hundreds of miles in 135 million years at a great speed (4 inches per year!!!) The Indian plate crashed into the Eurasian plate with such speed and force that it created the tallest mountain range on Earth, the Himalayas! What do you predict the world will look like in 100 million or 200 million years? What new mountain ranges will form? Where will new volcanoes erupt?

The Atlantic Ocean will be much larger 50 million years from now and the Pacific Ocean will be much smaller. North and South America will have moved farther west (California moving north) while Greenland will be located farther west but also farther north. The western part of Africa will rotate clockwise and crash into Europe causing great mountain building, while the far eastern region of Africa will rotate eastward toward the Arabian peninsula. Australia will move farther north into the tropics, while New Zealand will move to the south of Australia.

All of these predictions are just that, predictions. These movements of the continents may happen if the plates continue to move in the same direction and with the same speed as they are moving today. Scientists are not certain of the movement today, let alone 50 million years into the future.

What do you think the world will look like in 50 million years???

Write the answers for the questions on a sheet of paper. When you finish the lesson click on the "Earth" icon so that the next pair of students will be at the start of the lesson.

1. What caused Pangea to break up?

2. What is the Continental Drift Theory?

3. What happened at the Triple Junction? Where is it located today?

# How Earth's Plates Move Lesson #3

Geologists came to the conclusion in the 1960's that the Earth's rigid outer layer (crust and outer, rigid layer of the mantle) was not a single piece, but was broken up into about 12 large pieces called plates. The red lines on the map of the world above indicate

1. Convergent boundaries - two plates collide to form mountains or a subduction zone.

2. Divergent boundary - two plates are moving in opposite directions as in a mid-ocean ridge.

3. Transform boundary - two plates are sliding past each other as in the San Andreas fault of California. A transform boundary is like a tear in the Earth's crust. These plates move very slowly across the surface of the Earth as though they were on a conveyor belt. The convection currents in the much hotter mantle continually move the plates about 1/2 to 4 inches per year.

When the plates move they collide or spread apart allowing the very hot molten material called lava to escape from the mantle. When collisions occur they produce mountains, deep underwater valleys called trenches, and volcanoes. As mountains and valleys are being formed natural disasters such as earthquakes and volcanic activity can occur which has affected humans for thousands of years.

The Earth is producing "new" crust where two plates are diverging or spreading apart. This occurs in the middle of our great oceans. The mid-ocean ridges are the longest continually running mountain range in the world. These ridges are connected and are about 40,000 miles long!!

One of these mid-ocean ridges, the Mid-Atlantic ridge , is spreading apart making the Atlantic Ocean wider. As the two plates move the mantle melts, making magma and lava fill the void with newly formed rock. The bottom of the Atlantic Ocean is filled with some of the "youngest" crust on Earth. The island of Iceland, located in the North Atlantic, is still being formed at this Mid-Atlantic ridge.

The Atlantic Ocean is getting larger as the Western Hemisphere moves away from Europe and Asia. The Pacific Ocean, on the other hand, is becoming smaller and smaller. This is occurring because the North American and South American plates are moving westward toward Asia and Australia.

The North and South American plates are crashing into the thinner and denser oceanic plates of the Pacific. This drives the oceanic plates deep into the mantle destroying the oceanic plates. This boundary in which an oceanic plate is driven down and destroyed by a continental plate is called a subduction zone.

This Pacific Ocean region has more earthquakes and volcanic activity than any other area of the world. Because of all the volcanoes this region has been given the nickname of "The Ring of Fire" .

When the less dense, lighter continental plate overrides the oceanic plate a subduction zone forms. Because the oceanic plate is bent and driven down, a deep trench forms at this collison point. These trenches are the lowest points on the Earth's crust. One trench is a mile deeper than Mount Everest is tall!

As the oceanic plate descends into the mantle some of it melts. This material moves into the mantle above the plate and causes the mantle to melt. This liquid rock, called magma, rises to the surface because it is less dense then the surrounding rock. If the magma reaches the surface of the Earth, a volcano forms.

As the mantle rocks melt they form magma. The magma collects in a magma pool. Because the magma is less dense than the surrounding mantle material it will rise. Pressure in the magma cracks the overlying rocks. Then the magma injects into the crack. This process repeats thousands of times, bring the magma towards the surface.

A volcano will form if the magma reaches the surface. When magma does reach the surface it is then called lava.

As the volcano erupts it may build a mountain. The lava along with ash and other pyroclastic material will continue to build the mountain higher with each eruption.

The Cascade mountain range in the Western United States and the Andes Mountains in South America were formed in this way!!

This is a cross section of the Earth in the Southern Hemisphere. The map shows a subduction zone that has created the Peru-Chile Trench at the western edge of South America. This subduction zone has produced the Andes Mountains which run along the entire west coast of South America. It also shows you the Mid-Atlantic Ridge which is spreading the Atlantic Ocean making it wider and wider. The cross section shows two processes at work;

1. "Old Crust" being destroyed at a subduction zone and

2. "New Crust" being produced at the Mid-Atlantic Ridge.

The pink lines on this map of the Pacific Ocean represent deep ocean trenches. These trenches are some of the lowest points on the crust of the Earth. Marianas Trench north of New Guinea is the deepest point on the Earth's surface at 36,201 feet below sea level. Marianas Trench is 7,173 feet deeper than Mount Everest is high!!!!

Trenches surround almost all of the Pacific Ocean. Some of the other trenches of the Pacific are the Aleutian, Peru-Chile, Kuril, and the Japan trench.

There are trenches wherever continental plates and oceanic plates collide. The Java Trench in the Indian Ocean is the deepest point of that ocean at 24,442 feet below sea level.

Write the answers to the following questions in complete sentences on a piece of paper. Use the page titles located directly under the questions to move your way through the lesson to locate the answers. When you finish the questions click on the Earth icon to return the program to the beginning.

1. In your own words explain what happens at a subduction zone.

2. In your own words explain what happens at a mid-ocean ridge.

3. At a subduction zone what causes magma to rise?

# Chapter 1 Copymaster: Test, Reviews, Answer Keys, Chapter Schedule

Chapter #1 Copymaster includes tests and answers for students and teachers on material covered in Chapter 1.

Select options on the right hand side to proceed.

# Chapter 1 Lesson Plan

## Chapter 1 Lesson Plan

Explain to your class that they will be working in three centers for science over the next few weeks. They need a science notebook, a pencil, and colored pencils daily. Some days they will need more lab equipment.

Day one-
Materials:

1. Reading and Thinking Sheets for each student- See Content Lesson #1

2. Hands-On materials- See Hands-On Lesson #1
• 1 apple for every four students

• 1 knife for teacher use only!!

Split your class into 3 groups. Each group will start at a different center. The three centers are the Hands-On Center, the Content Center, and the Computer Center. Have books dealing with Earth Science at each center for those who finish their work early.
Each center will last approximately 15 minutes. When everyone in the class has finished their work in the center rotate the groups. When all the groups have been at each center review with the whole class by correcting the questions from the Computer Center and the Content Center.
If your class is very large you may want to set up a fourth center. This could be called the Vocabulary Center. There is a Student Vocabulary Sheet and a Teacher Vocabulary Sheet provided in the Copy Masters file.

Day Two
Materials:

• One copy of Lesson #2 Content Sheets for each student

• Hands-On Materials:
• Two maps (Pangaea, World today) for the students to study.
• Two "World Cut Up" maps for each student pair to cut into the seven moving continental plates.
• Two pieces of blue construction paper (9 X 12) that will represent the oceans of the world.
• Glue
• Scissors
• Colored Markers

Follow the same lesson plan for day one. Start the groups at a different center each day.

Day Three-

Materials:

• One copy of Content Lesson # 3 for each student

• Four strips of foam rubber 4 inches by 30 inches and about 1 inch thick. The foam rubber should be made of different colors. These strips will represent layers (strata) in the crust of the earth. (See Hands-On lesson #3)

Follow the same lesson plan design as in Day One and Two. Start the groups at a different center from the previous day

Day Four-
Review Vocabulary Sheets by playing a game called Baseball.
Materials:

• One die
• One baseball diamond transparency
• Four markers for the runners

Break your class into two teams.
Ask a student a question. If they answer correctly award them the base that they rolled with the die. (See rules below) If they answer incorrectly their team is out. One out per inning.

## Rules for the game

1. Shake the die
1. single
2. double
3. triple
4. home run
5. single
6. single

2. Ask the question-If they answer correctly award them the base that they rolled with the die. Place a marker on the base that they earned. If there is a runner on base ahead of them move the runner the same amount of bases as the batter. If they answer incorrectly their team is out. One out per inning.

3. Keep rolling and asking questions until a player answers incorrectly. When they answer incorrectly switch batting teams.

Day Five-
Have the students work on the Review provided in the Copy Masters.

Day Six-
Correct the Review and play Baseball or another review game. After the students have learned Baseball they can play it in their groups with copies of the diamond.

Day Seven-
Test the students using the Test provided in the Copy Masters.

# Baseball Game

## Materials:

• One die
• One baseball diamond transparency
• Four markers for the runners

## Instructions

Break your class into two teams.
Ask a student a question. If they answer correctly award them the base that they rolled with the die. (See rules below) If they answer incorrectly their team is out. One out per inning.

## Rules for the game

1. Shake the die
1. single
2. double
3. triple
4. home run
5. single
6. single

2. Ask the question-If they answer correctly award them the base that they rolled with the die. Place a marker on the base that they earned. If there is a runner on base ahead of them move the runner the same amount of bases as the batter. If they answer incorrectly their team is out. One out per inning.

3. Keep rolling and asking questions until a player answers incorrectly. When they answer incorrectly switch batting teams.

# Chapter 1 Review

Review Chapter 1
The Earth: A Dynamic Planet

Name____________________

1. Draw two diagrams showing the folding and fault-block mountain building process.

2. In your own words explain how convection currents in the mantle move the plates of the Earth.

Use the following terms to answer the questions 3-14 below.

 Collision plate boundary Transverse plate boundary Separation plate boundary Continental Drift Theory Pangea Plates Magma Trenches Lava Fault Laurasia Gondwanaland

3. The southern continent after Pangea split apart. It became the continents of Africa, Antarctica, South America and the subcontinent of India.

4. The plate boundary where two plates are moving apart creating new crust and making the oceans spread.

5. This is molten rock on the surface of the Earth.

6. This is the name of the supercontinent 250 million years ago.

7. These are pieces of the crust that "float" and move because of the mantle's convection currents.

# Chapter 1 Test

The Earth: A Dynamic Planet

Name______________________

1-4. Label the four layers of the Earth.

5. Explain how the mantle's convection currents move the Earth's plates?

6. What is happening at a transverse plate boundary?

7. Name two pieces of evidence that scientists have used to base the Continental Drift Theory on.

8. The collision of the Indian plate and the Eurasian plate produced the _______________________ Mountains, the highest mountain range in the world.

9. What type of mountain formation is shown in the diagram below?

10. What type of mountain formation is shown in the diagram below?

What is happening at the following plate boundaries?

11. Collision boundary-

12. Separation boundary-

13. Transverse boundary-

Matching Vocabulary I

 14. _____ subduction zone A Pieces of the crust that "float" on the mantle. 15. _____ convection currents B The only ocean on Earth 250 million years ago. 16. _____ Pangea C Movements in a material caused by hotter material rising and cooler material sinking. 17. _____ Plates D Supercontinent 250 million years ago 18. _____Panthalassa E Area where two plates are colliding. One plate is pushed down under the other plate.

Matching Vocabulary II

 19. _____Magma A The northern half of Pangea after it split apart. 20. ___Continental Drift Theory B The deepest places on the surface of the Earth. They are located at subduction zones. 21. ______Mid-ocean ridge C Molten rock below the surface of the Earth 22. _____ Laurasia D Place where two plates are separating. These plates are moving in opposite directions making the oceans larger. 23. _____Trenches E The idea that the Earth's plates are "floating" on the mantle and have been for millions of years.

Review Chapter 1
The Earth: A Dynamic Planet

1. Draw two diagrams showing the folding and fault-block mountain building process.

Fault-block mountain building process

Folding Process

2. In your own words explain how convection currents in the mantle move the plates of the Earth.

The deepest portion of the mantle is much hotter than the upper mantle. Hot material rises to the top of the mantle and then cools and sinks. This rising and sinking happens in a circular motion which turns over and over. As it turns it moves the upper region of the mantle and the crust with it.

Use the following terms to answer the questions 3-14 below.

 Collision plate boundary Transverse plate boundary Separation plate boundary Pangea Plates Magma Continental Drift Theory Trenches Lava Fault Laurasia Gondwanaland
3. The southern continent after Pangea split apart. It became the continents of Africa, Antarctica, South America and the subcontinent of India.
Gondwanaland
4. The plate boundary where two plates are moving apart creating new crust and making the oceans spread.
Separation Plate Boundary

5. This is molten rock on the surface of the Earth.
Lava

6. This is the name of the supercontinent 250 million years ago.
Pangea
7. These are pieces of the crust that "float" and move because of the mantle's convection currents.
Plates
8. Molten rock under the surface of the Earth is called.
Magma
9. The northern continent after Pangea split.
Laurasia
10. A long crack in the crust is called a  Fault .

11. A plate boundary in which the two plates crash into each other causing mountain building, earthquakes, and volcanic activity.
Collision Plate Boundary

12. The idea that the Earth's plates are moving across the surface of the Earth.
Continental Drift Theory

13. A plate boundary in which the two plates are sliding in opposite directions.
Transverse Plate Boundary
14. The deepest area of the oceans. They are formed at a subduction zone.
Trenches
15. What is the main material that the crust is made of?
Rock
16. What two metals are the main components of the inner and outer core?
Iron and Nickel

17. Name three pieces of evidence that scientists have used to base their ideas for the Continental Drift theory on.

### Scientists have used magnetic bands in rocks to prove that the continents have drifted apart, fossils of tropical plants and animals that have been found in places like Antarctica and Greenland, and fossils of fish found in high mountain regions.

18-21 Label the four layers of the Earth and explain what the main materials are that make up each layer.

1.Crust 2.Mantle 3.Outer Core 4. Inner Core

# Chapter 1 Test Answer Key

he Earth: A Dynamic Planet

1-4 Label the four layers of the Earth.

1.Crust 2.Mantle 3.Outer Core 4. Inner Core

5. Explain how the mantle's convection currents move the Earth's plates?
The deepest zone of the mantle is much hotter than the upper zone. Hot material rises to the top of the mantle and then cools and sinks. This rising and sinking happens in a circular motion. When the mantle flows it moves the plates.

6. What is happening at a transverse plate boundary?
A transverse plate boundary has two plates sliding by each other. Both plates are moving in opposite directions. A transverse boundary is like a tear in the Earth's crust.

7. Name two pieces of evidence that scientists have used to base the Continental Drift Theory on.
Scientists have used 1)magnetic bands in rocks and 2)fossils of tropical plants and animals that have been found in places like Antarctica and Greenland. They have also used fossils of fish found in high mountain regions in the center of continents.

8. The collision of the Indian plate and the Asian plate produced the Himalaya Mountains, the highest mountain range in the world.

9. What type of mountain formation is shown in the diagram below?

Folded Mountains

10. What type of mountain formation is shown in the diagram below?

Fault-block Mountains

What is happening at the following plate boundaries?
11. Collision boundary-
Two plates are crashing into each other causing mountain building, volcanic activity, and earthquakes.
12. Separation boundary-
Two plates are moving in opposite directions causing magma to fill the void and producing "NEW" crust. This is also spreading the oceans making them wider.
13. Transverse boundary-
Two plates are sliding past each other moving in opposite directions.

Matching Vocabulary I
 14. __E__ subduction zone A Pieces of the crust that "float" on the mantle. 15. __C__ convection currents B The only ocean on Earth 250 million years ago. 16. __D__ Pangea C Movements in a fluid caused by hotter material rising, then cooling and sinking in a circular motion. 17. __A__ Plates D Supercontinent 250 million years ago 18. __B__Panthalassa E Area where two plates are colliding. One plate is pushed down under the other plate.

Matching Vocabulary II
 19. __C__Magma A The northern half of Pangea after it split apart. 20. __E__Continental Drift Theory B The deepest places on the surface of the Earth. They are located at subduction zones. 21. __D__Mid-ocean ridge C Molten rock below the surface of the Earth 22. __A__Laurasia D Place where two plates are separating. These plates are moving in opposite directions making the oceans larger. 23. __B__Trenches E The idea that the Earth's plates are "floating" on the mantle and have been for millions of years.

# Chapter 1 Student Vocabulary

Vocabulary
Chapter 1
The Earth; A Dyanamic Planet

Name____________________

Lesson 1 The Earth's Layers

1. Crust-

2. Oceanic Crust-

3. Continental Crust-

4. Mantle-

5. Convection Currents-

6. Outer Core-

7. Inner Core-

Lesson Two- Pangea to the present

1. Dynamic Planet-

2. Plates-

3. Plate Tectonics/Continental Drift Theory-

• Pangaea-

• Panthalassa-

• Laurasia-

• Gondwanaland-

4. Plate Boundaries
• Convergent-

• Divergent-

• Transform-
5. Myths and Legends
• Japan-Namazu and Kashima

• Hawaii- Pele

• Roman-Vulcan

Lesson 3- How Plates Move

1. Subduction Zone-

2. Mid-ocean ridge-

3. Magma/Magma Pool-

4. Pyroclastic Rock-

5. Trenches-

6. Formation of Mountains-

# Chapter 1 Teacher Vocabulary

Vocabulary
Chapter 1
The Earth; A Dynamic Planet

Name____________________

### Lesson 1 "The Earth's Layers"

1. Crust -The outer layer of the Earth. The crust consists of ocean plates and continental plates. The crust is composed of light material called rock. The crust and the outer layer of the mantle together are called the lithosphere. The lithosphere is very brittle and light and moves because of convection currents in the lower layer of the mantle called the asthenosphere.

2. Oceanic Crust -Made of dense basaltic rock. Oceanic plates carry the continental plates across the surface of the Earth.

3. Continental Crust -Made of light granitic rock. Continental crust rides on the oceanic crust.

• Lithosphere - The crust and the upper rigid layer of the mantle seem to move together and form the plates of the Earth.

4. Mantle -Largest layer of the Earth located directly under the crust. The mantle is composed of very hot, dense, flowing rock. The material in the mantle flows because of convection currents.

• Asthenosphere - Lower layer of the mantle. This is the layer that flows and moves the plates of the Earth. Flows very slowly with the consistency of hot asphalt under pressure.

5. Convection Currents - are a circular current caused by the difference in temperatures from the bottom to the top of the mantle. It is because of these currents that the plates of the Earth have moved in the past and are moving today. These plate movements cause earthquakes, mountain building, and volcanism.

6. Outer Core -The layer located directly under the mantle. The outer core is composed of liquid nickel and iron. Scientists believe that the outer core is liquid because S waves from an earthquake bounce of the layer instead of passing through it.

7. Inner Core -The inner core is composed of nickel and iron under such great temperatures and pressures that the metals are in a solid state of motion.

### Lesson Two- "Pangaea to the present"

1. Dynamic Planet -The Earth's surface is very slowly but constantly changing. The plates are moving causing earthquakes that reshape the land, mountain building, and volcanism that also dramatically reshapes the surface.

2. Plates -The thin, fragile, and rigid lithosphere is broken up into 12 main plates. These plates move very slowly at about 1 inch to 4 inches per year.

3. Plate Tectonics/Continental Drift Theory -Alfred Wegener, a German scientist proposed this theory that states that the Earth's surface is broken into pieces that move and have moved for millions of years. Wegener did not know the mechanism that moved the plates, and his theory was rejected until the 1960's when scientists studied the ocean floor and found the mid-ocean ridges (sea floor spreading zones).
• Pangaea -Super continent 250 million years ago. The seven continents were all connected together into one huge land mass.
• Panthalassa -The gigantic ocean 250 million years ago. It was the predecessor to the Pacific Ocean.
• Laurasia -About 200 million years ago Pangaea began to break up. The northern part which consisted of North America, Asia, and Europe was then called Laurasia.
• Gondwanaland -The southern part after the split up of Pangaea was called Gondwanaland. Gondwanaland consisted of South America, Africa, Antarctica, Australia and the subcontinent of India.

4. Plate Boundaries
• Convergent -A boundary in which two plates collide causing
1) immense mountain building (Ex: Indian plate and the Eurasian plate forming the Himalayan Mountains) and
2) one plate riding above the other driving the thinner denser plate down into the mantle creating a subduction zone
• Divergent -A boundary in which two plates are separating. The two plates are moving in opposite directions and as they spread apart magma fills the void causing the formation of new crust. Divergent boundaries cause the oceans to spread apart while convergent boundaries cause the oceans to shrink.
• Transform -A boundary in which two plates scrape and slide past each other. Transform boundaries are like tears in the Earth's crust. An example is the San Andreas Fault in California.

### Lesson 3- How Plates Move

1. Subduction Zone -Formed at a convergent plate boundary. One plate is lighter and thicker than the other causing the thinner denser plate to be driven down into the mantle. Subduction zones are areas of the world in which high amounts of earthquakes and volcanism is present. Subduction zones are ocean shrinking zones.

2. Mid-ocean ridge -Formed at a divergent plate boundary. The worlds longest continuous mountain range over 40,000 miles long. Where the two plates separate lava fills the void causing new crust to be produced. Mid-ocean ridges are ocean spreading zones.

3. Magma/Magma Chamber -Magma is molten rock under the Earth's surface. Magma is full of gas and under extreme pressures. Magma will collect in areas of weak rock far under the surface of the Earth in zones called magma chambers.

4. Pyroclastic Rock -Pyroclastic is a Greek word that means "broken by fire". Pyroclasts are fragmented rock that is ejected from a volcano. Pyroclasts are classified by the size of the particle; ash is very small pieces of shattered rock. lapilli are pieces of shattered rock 1/10 of an inch to 2 inches in diameter. Blocks and bombs are larger pyroclasts ranging in size from 2 inches to several feet in diameter. Blocks are angular chunks of rock and bombs are rounded rock that takes its shape as it is hurled through the air.

5. Trenches -Form at subduction zones. They are the deepest part of the oceans and the lowest points on the crust of the Earth.

6. Formation of Mountains -
• Folded Mountains -Rollercoaster like formation. The plates of the Earth are pushed together and the impact forms the tallest mountains on Earth.

• Fault-block Mountains -The plates are pushed together and snap from the collision. These mountains have very rough linear peaks. Ex: The Grand Teton Mountains in Wyoming.

• Dome Mountains -These mountains form when plate collisions push an area of the crust up into a dome shape. The crust doesn't snap and break as in fault-block mountains. Ex: The Black Hills of South Dakota.

# Lesson #1 Goals, Objectives, and Materials

Goals, Objectives and Materials
For Lesson #1
The Earth's Layers

### Goal:

To provide students with the understanding that the Earth is comprised of four layers.

### Objectives:

The students will be able to

1. Name and label the four layers of the Earth;
2. Identify the main minerals that make up each layer;
3. Explain how scientists formulated the idea that the Earth is comprised of four layers.

### Materials:

1. One "Earth's Layers" disk for each computer
2. Reading and Thinking Sheets for each student- See Content Lesson #1

3. Hands-On materials- See Hands-On Lesson #1
• 1 apple for every four students
• 1 knife

# Lesson #2 Goals, Objectives, and Materials

Goals, Objectives and Materials
For Lesson #2
"Pangaea to the Present"

### Goals:

To acquaint students with the concept that the Earth is a dynamic ever changing planet. To help students to understand that the Earth's plates have been moving for millions of years and are still moving today.

### Objectives:

The students will be able to:

1. Demonstrate how the Earth's plates have moved.
2. Describe the processes that cause plate movement.

### Materials:

1. One copy of Lesson #2 Content Sheets for each student

Hands-On Materials:

1. Two maps (Pangaea, World today) for the students to study.
2. Two "World Cut Up" maps for each student pair to cut into the seven moving continental plates.
3. Two pieces of blue construction paper (9 X 12) that will represent the oceans of the world.
4. Glue
5. Scissors
6. Colored Markers

# Lesson #3 Goals, Objectives, and Materials

Goals, Objectives and Materials
For Lesson #3
"How the Earth's Plates Move"

### Goals:

To help students understand the concept of plate tectonics.

### Objectives:

Students will:

1. Become familiar with and be able to demonstrate the process of folding;

2. Become familiar with the process of convection current movement in the asthenosphere;

3. Become familiar with processes that produce convergent, divergent, and transform plate boundaries.

### Materials:

1. One copy of Content Lesson # 3 for each student

2. Four strips of foam rubber 4 inches by 30 inches and about 1 inch thick. The foam rubber should be made of different colors. These strips will represent layers (strata) in the crust of the earth. (See Hands-On lesson #3)

# Lesson #1 Content Center

### Content Center (Lesson #1)The Earth's layers

Geologists have known for about 100 years that the Earth is composed of four layers; the Crust, Mantle, Outer Core, and the Inner Core . Scientists still argue about the makeup of these layers and exactly how each layer interact.
A geologist, by the name of Andrija Mohorovicic, discovered in 1909 that earthquake waves near the surface moved slower than earthquake waves that passed through the interior of the Earth. He also noticed that the P (primary, first and strongest) waves that passed through the interior of the Earth did not do so in a straight line. These waves were bent or deflected by something!!! (see diagram A page 3)
He decided that the outside layer or Crust was made of less dense material (Rock) and the next layer, the Mantle was much denser. This would explain why the earthquake waves moved slower through the crust. Waves of all kinds move faster and straighter through denser, more solid objects.
Today scientists believe that the crust and the rigid, outer zone of the mantle makes up a layer that is called the Lithosphere . The lithosphere is broken into 12 large pieces that are called plates. The zone directly under the lithosphere is made of a flowing, denser layer called the Asthenosphere. Scientists believe that the plates ride on the asthenosphere, which flows due to convection currents. See diagram on page 2.

### Beno Gutenberg

a German geologist, believed that the Outer Core must be made of a liquid because the slower S (secondary waves) could not pass through this layer and in fact "bounced off" and were deflected many degrees off course. Study diagram A on page 3.

The fourth layer, the Inner Core, is composed of very, very hot metals (iron and nickel) with pressures so great that the metals do not flow as a liquid, but are forced to vibrate in place like a solid. Earthquake waves that reach this layer move at the greatest speeds because waves move through solids faster than through gases and liquids.
To honor Mohorovicic, scientists have named the boundary between the crust and the mantle the Mohorovicic discontinuity or the "MOHO" for short. Beno Gutenberg discovered the boundary or discontinuity between the mantle and the outer core. This boundary was named after him, the Gutenberg discontinuity. See diagram B.

# Discussion Questions

1. How did Andrija Mohorovicic discover that the Earth's crust was made of less dense rock than the mantle.
2. Write in your own words the definition of a discontinuity.

# Lesson #2 Content Center

### CONTENT CENTER (PANGAEA TO THE PRESENT )Lesson # 2Plate Tectonics(The Continental Drift Theory)

Earthquakes, volcanoes, and mountains are all produced by the same natural processes. We know this to be true today, but even as little as one hundred years ago scientists were unsure as to how these geologic processes occurred.
The ancient Japanese legend of Namazu  explained why earthquakes occur this way. Namazu was a giant catfish that lived under the surface of the Earth. It would shake violently and cause great destruction from time to time.  Kashima, who is a Japanese god, was the only god that was strong enough to control Namazu. Kashima would hold Namazu down and pin the catfish under a rock. When Kashima's mind would wonder, Namazu would escape and cause another earthquake.
Many cultures have tried to explain why earthquakes and volcanoes occur through stories about their gods and goddesses. The Hawaiian Islanders thought that volcanoes were the home of the fire goddess Pele. The Romans believed that the blacksmith god, Vulcan, used volcanoes as his forge to produce weapons.
For hundreds of years people throughout the world explained earthquakes and volcanoes through myth and legend. In 1620 however Sir Francis Bacon of England declared that it was not gods and goddesses that caused natural disasters. He noticed how the coasts of Africa and South America were very much alike. In fact they could almost fit together like pieces of a jigsaw puzzle. The map on the next page shows how the two continents could fit together.

As humans traveled the world they noticed seashells high in mountains many miles from the nearest ocean. Why is there a similarity between the coasts of Africa and South America? How did those seashells end up high in the mountains? These questions along with new discoveries lead scientists to believe that the Earth is a dynamic, or constantly changing planet. It was not until the 1960's though, that scientists started to agree to the concept that the continents could move across the surface of the Earth.
A German meteorologist by the name of Alfred Wegener showed that rock bands in South America and rock bands in Africa matched mineral content and by age exactly. He also showed that the magnetic bands in these same rocks did not point to the magnetic north pole as they should. If the continents could be moved back into the position that they were created, then they do point to the magnetic north pole. Wegener concluded that the continents must have drifted apart hundreds of miles. He did not however have an explanation as to how these massive continents could move such a great distance.
It was not until the 1960's that geologists gained the technology to fully understand the processes that could move the Earth's plates. They concluded that the Earth's surface was composed of not one large sheet but was composed of more than twelve major pieces of crust. Geologists call these pieces plates . These plates float across the surface of the Earth like an iceberg floats on the ocean. The driving force behind these plate movements are the convection currents in the mantle. The convection currents turn very slowly dragging the plates along with these movements. The convection currents move the plates very slowly. These plates move at only 1 to 4 inches per year!!
The lines on the map of the world on page 4 indicate the position of the plate boundaries. Boundaries are places where the plates meet.
Now geologists can finally explain the reasons that mountains are built, volcanoes erupt, and earthquakes occur. The Plate Tectonics Theory of continental movement can explain scientifically why all of these geologic processes can occur. Humans no longer have to try to explain these natural occurrences through myth and legend.

## Review Questions

1. In your own words explain what the Continental Drift Theory states.
2. How did Alfred Wegener try to prove that the continents of Africa and South America were once connected.
3. How did the ancient people of Japan explain earthquakes?
4. How did the ancient Romans explain the presence volcanoes.

# Lesson #3 Content Center

### Content CenterPlate Movements(Lesson #3)(Mountain Building)

The great mountain ranges of the world were created because of the constant but very slow movement of the Earth's plates. When the plates of the Earth collide the crust folds into high mountain ranges. The roots of the world's great mountain ranges contain some of the oldest rocks on the surface of the Earth. Some of these rocks are over 3.5 billion years old!! These rocks were once buried deep inside the Earth and have been raised into mountains by the collisions of the plates.
These plates travel at a very slow rate about 1 to 4 inches per year. The Indian Subcontinent was a very fast mover, clipping along at over 4 inches per year. When it slammed into the Eurasian plate over 24 million years ago the collision built the highest mountain range in the world, the Himalayas. In fact, the Himalayas are still climbing higher and higher today.
Math Connection
How many miles would a plate travel in 100 million years at a rate of 1 inch per year? (Hint: Divide 100,000,000 inches by 12 inches per foot and then divide that answer by 5280 feet in a mile). Answer- In 100 million years the plate would travel about 1578 miles.

There are five ways that mountains are formed
1. Volcanic activity
2. Folding
3. Faulting
4. Dome building
5. Erosion

In this lesson we are going to concentrate on the processes of 1)Folding, 2)Faulting, and 3)Dome building.
All rock that is put under extreme pressure for long periods of time (thousands or millions of years) will fold like clay.  Folding is a process in which the Earth's plates are pushed together in a roller coaster like series of high points and low points. Folding bends many layers of rocks without breaking them. The Appalachian Mountains and Rocky Mountains of the United States, and the Alps of Europe are examples of mountain ranges that were formed by folding.
Folded Strata (Layers)

Many of the greatest mountain ranges of the world have formed because of enormous collisions between continents. The Appalachian Mountains in the Eastern United States were formed about 400 million years ago when North America and Africa collided.

400 million years ago

The areas (next page) represented in yellow (white) are major mountain ranges that were formed by collisions of the continents millions of years ago!!!

Mountains sometimes form when many layers of the Earth's crust are moved vertically upward at fault lines by pressures caused by plates colliding. Fault lines are great cracks in the crust. The mountains that are formed in this way are called fault-block mountains.  The Sierra Nevada mountains in California and Nevada, and the Grand Teton range of Wyoming are examples of fault-block mountains.

The Black Hills of South Dakota and Wyoming, and the Adirondack Mountains of New York are low mountains that were formed when the crust was heaved upward without folding or faulting into a rounded dome. These are called Dome Mountains.  Dome mountains are much higher in elevation than the surrounding land and because of this erosion occurs at a very fast rate.

Thought and Discussion Questions
1. What are the 5 causes for mountain building?
2. What is the difference between how folded mountains and block-fault mountains are formed.
3. How do dome mountains form?

# Lesson #1 Hands-on Center

## Eating the Earth

Materials:

1. One-fourth of an apple for each student
2. 1 knife

The teacher will cut each apple into four pieces, cutting from the top (stem side) down through the core. Each student should receive 1/4 of an apple. The teacher will point out the similarities between the apple and the Earth's layers (see notes below).

The skin of the apple will represent the crust of the Earth. The teacher will point out how thin the skin is in comparison to the "meat" and the core. Explain to the students that the crust compared to the rest of the Earth is much thinner than the skin is to the rest of the apple.
The "meat" of the apple will represent the mantle of the Earth. Explain to the students that the mantle is the largest layer of the Earth. The mantle is composed of molten rock that is in a semi-plastic state. The mantle's composition is similar to very hot asphalt.
The core of the apple will represent the outer and inner cores of the Earth. Make sure that the students understand the Earth's core is composed of two layers. Point out that the core is like a little round ball in the middle of the Earth. The outer core is actually composed of very hot liquid metals, nickel and iron. The inner core is composed of the same nickel and iron but in a solid state because of intense pressure.
The students should have a science experiment notebook. Instruct them to draw and label a diagram of this and every hands-on experiment. Direct the students to write notes of what they learn as the experiment is being conducted.
The students should draw a model of the layers of the Earth in their science notebooks labeling the crust, mantle, and the core.
The students may eat the model of the Earth after the demonstration!

# Lesson #2 Hands-on Center

## Jigsaw World

Materials:

1. Two maps (Pangaea, World today)
2. Two "World Cut Up" maps
3. Two pieces of blue construction paper (9 X 12)
4. Glue
5. Scissors
6. Markers

1. The students will study the "World Today Map" (The black arrows indicate the direction of plate movement) and the "Pangaea/Panthassla Map".
2. Instruct the students to cut the two "World Cut Up" maps on the red lines.
3. The students will then place and paste the continents at the position that they were located 250 million years ago in the great ocean called Panthassla.
4. The students will then make a prediction of what the world will look like in 100 million years. The students should use the "World Map Today" in making their predictions.
5. Instruct the students to place the remaining continent cutouts and paste them onto the other piece of blue construction paper.
6. The students should also predict where new mountains will form and where new volcanoes will erupt by marking them on their prediction maps using markers.
7. Have the students write in their science notebooks what their reasons were for placing the continents where they did.

# Lesson #3 Hands-on Center

### Hands-on Center(How Plates Move)Lesson #3

Building Mountains
Modified and adapted from John Farndon's book
How the Earth Works
Materials:

1. Four strips of foam rubber 4 inches by 30 inches and about 1 inch thick. The foam rubber should be made of different colors. These strips will represent layers (strata) in the crust of the earth.

The students will set the strips in alternating layers as shown above. They will push the four layers from each end causing the layers to fold into an upside down U shape. This will represent the folding process. The upside U will represent a geologic feature called an anticline (mountain peak).
The students will also push the layers from each end causing the four layers to fold into a U shape. This U shape will represent a geological feature called a syncline (valley).
The teacher will explain that this is a simplified version of how folded mountains are formed and that the anticlines are the peaks and the synclines are the valleys of the mountain range.

Building Mountains II
Modified and adapted from John Farndon's book "How the Earth Works"

Materials:
1. Two colors of modeling clay
2. Two wooden blocks 4 in. x 6 in. x 4 in. or larger

The students will lay the modeling clay flat in alternating layers. These layers of clay will represent layers (strata) in crust of the Earth. The wooden blocks will be placed one at each end of the clay layers. the students will push the blocks toward each other very, very slowly. This pushing of the blocks will represent the movement of the continental plates. The students will see the folding process in action as they build their own mountain (Anticline).

After the students have built their mountains they could cut the clay mountains in the middle, this represents plates moving apart at a fault zone. This is what happened to South America and Africa. The students should put them back together looking for the similarities between the layers. The teacher will tell the students that this is exactly how geologists tried to prove the plate tectonics theory of plate movement.

# Discussion Questions

### Lesson 1 "The Earth's Layers"

Discussion Questions

1. How did Andrija Mohorovicic discover that the Earth's crust is made of less dense rock than the mantle.

2. Write in your own words the definition of a discontinuity.

3. Name the four layers of the Earth in order from the outside to the
center of the Earth.

4. What causes the mantle to "flow"?

5. What are the two main metals that make up the outer and inner core?

6. Describe in your own words how the Earth's layers were formed. Card 2 "The Four Layers" will help you

Lesson 2 "Pangea to the Present"

### Discussion Questions

1. In your own words explain what the Continental Drift Theory states.

2. How did Alfred Wegener try to prove that the continents of Africa and South America were once connected.

3. How did the ancient people of Japan explain earthquakes?

4. How did the ancient Romans explain the presence volcanoes.

## Lesson 3 "How Plates Move"

Discussion Questions

1. What causes mountain building?

2. What is the difference between how folded mountains and block-fault mountains are formed.

3. How do dome mountains form?

4. In your own words explain what happens at a subduction zone.

5. In your own words explain what happens at a mid-ocean ridge.

6. At a subduction zone what causes magma to rise?

# Discussion Questions

### Lesson 1 "The Earth's Layers"

Discussion Questions

1. How did Andrija Mohorovicic discover that the Earth's crust is made of less dense rock than the mantle.
By studying earthquake waves. The waves moved at diferent speed and at different angles through the different layers .

2. Write in your own words the definition of a discontinuity.
A discontinuity is the boundary between the layers of the Earth.
3. Name the four layers of the Earth in order from the outside to the
center of the Earth.
1.Crust 2. Mantle 3. Outer Core 4. Inner Core

4. What causes the mantle to "flow"?
The mantle flows because of convection currents that are caused by very hot material in the mantle rising, cooling, and then sinking. This circular pattern causes the mantle to flow.

5. What are the two main metals that make up the outer and inner core?
Nickel and Iron

6. Describe in your own words how the Earth's layers were formed. Card 2 "The Four Layers" will help you.
As the Earth cooled the densest, heaviest materials sank to the middle of the Earth. The lightest materials rose to the top. This material was made mostly of rock. Rock makes up the crust of the Earth. Denser rock makes up the mantle. The most dense materials, iron and nickel, make up the inner and outer core.

## Lesson 2 "Pangea to the Present"

### Discussion Questions

1. In your own words explain what the Continental Drift Theory states.
The Earth's plates are moved very slowly, 1-4 inches per year, by convection currents emenating from the mantle. These plates have been moving for millions of years and continue to move today.

2. How did Alfred Wegener try to prove that the continents of Africa and South America were once connected.
Alfred Wegener discovered that the magnetic bands in rocks from South America did not point ot the north pole as they should. If these rocks were moved to the position that Wegener though they were created then they did point ot the northpole. He also matched rocks from Africa and South America for mineral content and age.

3. How did the ancient people of Japan explain earthquakes?
The Japanese explained that earthquakes were produced by a giant catfish called Namazu. This catfish lived under the Earth's surface and shook very violently when it was not kept under control by the god Kashima.

4. How did the ancient Romans explain the presence volcanoes.
Vulcan, the god of weapons, used the volcanoes off the coast of the Roman Empire as his forge.

## Lesson 3 "How Plates Move"

Discussion Questions

1. What causes mountain building?
Mountains are formed from the Earth's plates movements. As plates crash into each other they push the crust up high into mountains.

2. What is the difference between how folded mountains and block-fault mountains are formed.
Folded mountains form into rollercoaster like formations. The layers are bent but not broken. When block-fault mountains are formed the layers are pushed up and broken into high sharp peaks and valleys.

3. How do dome mountains form?
Dome mountains form when the layers of the Earth don't break or fold but are pushed up into a rounded dome shape.

4. In your own words explain what happens at a subduction zone.
Two plates come together, one overriding the other at a subduction zone. The oceanic plate, which is thinner and denser, is driven under the continetal plate and into the mantle. A deep ocean trench is produced at the subduction zone.

5. In your own words explain what happens at a mid-ocean ridge.
Two plates are separating with magma welling up and filling the void with newly produced crust. These spreading plates are making the oceans wider and wider while the subduction zones are making the oceans smaller and destroying old crust.
6. At a subduction zone what causes magma to rise?
The oceanic crust and the upper layer of the mantle melts as it is driven into the mantleThe oceanic crust is not as dense as the mantle is. Because this material is less dense it will rise.