September 23, 2010. Warm up: Read the short article entitled “What evidence is there that the continents were once all connected?”, write the main ideas.

CHAPTER 9: PLATE TECTONICS

September 23, 2010

Warm up: Read the short article entitled “What evidence is there that the continents were once all connected?”, write the main ideas next to the paragraphs.

(this will not be a warm-up you turn in with your others)

What are some of the main ideas of the reading?

Objective:

• I will be able to describe the evidence supporting the theory of Continental Drift.

Key Points

Continental Drift was Alfred Wegner’s hypothesis to explain how Earth’s continents were once joined into a large landmass.The supercontinent was called “Pangaea”Pangaea began to break apart around 200 million years agoEvidence for this theory includes:

Continental Puzzle Matching Fossils

Matching rock types and formationsAncient Climates

Wegner’s Theory

Questions he (and many others had)…• Why do earthquakes occur?• How do volcanoes form?• Why do mountains form where they form?• What causes tsunamis?• Why is the Atlantic Ocean widening?

Wegner’s Theory (how he EXPLAINED these occurrences)

• The present-day continents drifted to their current positions.

• They were once joined together in one giant, supercontinent called Pangaea

Pangaea began to break apart about 200 million years ago

Evidence for Wegner’s Theory

1.The continental puzzle2.Matching fossils3.Rock types and structures4.Ancient climates

Evidence for Wegner’s Theory

1. The continental puzzleFOR: Similarities are found along the

coastlines of the continents, especially South America and Africa

AGAINST: Erosion could change the coastlines’ shapes over time

Evidence for Wegner’s Theory

2. Matching fossilsFOR: Several fossil organisms are found far

apart on different continentsAGAINST: Ancient land bridges may have

existed to allow the animals and organisms to spread (BUT! There is no fossil evidence of these organisms under the ocean)

Continental Puzzle and Fossil Evidence

• What about the shapes of the continents suggests that they were once joined together into 1 large landmass?

• Discuss the fossil patterns you discovered… how do these patterns provide evidence that the continents were all once joined?

Discuss the following questions with your partner

Key Points of Today

• Continental Drift is the theory that

Evidence for Wegner’s Theory

3. Rock Types and StructuresFOR: Mountain belts that end on one

continent reappear on another

Evidence for Wegner’s Theory4. Ancient ClimatesFOR: There is evidence that glaciers once covered Australia,

South America, India, and AfricaAGAINST: Global climate changes could have allowed glaciers to

form at lower latitudes than expected

One little problem…

• How do the continents move?• Wegner tried to explain the movements as

the result of tidal forces• Physicists quickly dismissed this- the force

necessary would have stopped the Earth’s rotation!!!

Check-in before you check-out

1. What is the name of the hypothesis that states the continents were once joined to form a supercontinent?

2. The 4 pieces of evidence that support Wegner’s hypothesis are

3. Why was Wegner’s hypothesis rejected?

Make a comic strip about Continental Drift

• You have 6 “frames” to fill with the story of continental drift.

• Your first frame should depict and describe Wegner’s idea

• Your second, third, fourth, and fifth frames should depict and describe each of the pieces of evidence for the theory

• Your last frame should depict and describe the main problem with the theory.

Brownie Ticket 9/241. Evidence about ancient climates indicates that:

a. continents in the Southern Hemisphere today were once centered over the North Pole

b. continents in the Northern Hemisphere today were once centered over the South Pole

c. glacial ice once covered much of what is now India and Australiad. no continents occupied the Southern Hemisphere

2. What hypothesis states that the continents were once joined to form a single supercontinent? ________________________

3. What was the main reason Wegener’s continental drift hypothesis was rejected?

a. He was not well liked by other scientists.b. He could not provide a mechanism for the movement of the continents.c. His evidence was incorrect.d. He could provide only illogical explanations for the movement of the

continents.

Warm-Up 9/24/101. What hypothesis states that the continents were

once joined to form a single supercontinent?2. Name the four evidences that support Wegener’s

hypothesis.3. Evidence about ancient climates indicates that

_______ once covered these four continents:4. What was the main reason Wegener’s

continental drift hypothesis was rejected?

Announcements

• MINERALS PROJECT IS DUE TODAY!

• Please email it to me or make sure it is on my flash drive before leaving school today!

• Remember, Article Reports are due on Monday!

Objectives – TODAY:

• I will be able to describe the different types of plate boundaries.

• I will be able to compare and contrast the theory of plate tectonics with the theory of continental drift.

Key Points • According to the theory of plate tectonics the

lithosphere is divided into plates.• In the plate tectonics theory, the lithosphere is divided

into 7 major plates and many smaller plates• A transform-fault boundary is the kind of plate boundary

that occurs where two plates grind past each other without destroying or producing lithosphere.

• A convergent boundary occurs where two plates move together, causing one plate to descend into the mantle beneath the other plate.

• A divergent boundary occurs when two plates move apart creating new seafloor.

Questions that remained after Wegner

• Why do earthquakes occur?• How do volcanoes form?• Why do mountains form where they form?• What causes tsunamis?• Why is the Atlantic Ocean widening?• Why does the earth seem to be moving?

The lithosphere is the uppermost part of the mantle. It is made of solid rock.

• According to the theory of plate tectonics, the lithosphere is divided into plates.

• The plates move around on the asthenosphere.

• The asthenosphere is a part of the mantle that is partially melted. (magma!)

• In the plate tectonics theory, the lithosphere is divided into 7 major plates and many smaller plates.

• These plates are constantly moving. • They can run into each other head-on, move apart, or slide past

one another.

Divergent Boundaries• A divergent boundary occurs when two plates

move apart creating new seafloor.• A new divergent boundary is located in Africa

and is called the East African Rift valley.

Spreading Center

East African Rift Valley

Convergent Boundaries• A convergent boundary occurs where two plates move

together, forcing one plate underneath the other.

• This can cause mountains to form and creates volcanoes.

Transform-Fault Boundaries• A transform-fault boundary occurs where two

plates grind past each other without destroying or producing lithosphere.

• The San Andreas fault in CA is an example.

The San Andreas Fault

Three Types of Plate Boundaries

Solving the Problem• Unlike the theory of Continental Drift, using

the theory of plate tectonics, scientists have explained WHY the plates move.

• The movement of the plates is driven by the unequal distribution of heat within the earth.

Solving the Problem• Hot material found deep in the mantle moves

slowly upward.

• At the same time, cooler, denser slabs of oceanic lithosphere sink into the mantle.

• This movement causes earth’s crust to move.

Check-In Questions

• In the theory of plate tectonics, what is divided into plates?

• Name the three types of plate boundaries.

• What causes the plates to move?

Compare and Contrast

• Compare the theory of Plate tectonics with the theory of Continental Drift.

• Create a Venn Diagram either on paper or using your computer.

• Make sure to include: – At least 2 things they have in common– At least 2 things that just apply to plate tectonics– At least 2 things that just apply to continental drift

Three Types of Plate Boundaries

Spreading Center

Brownie Ticket 9/24/101. According to the theory of plate tectonics,

a. the asthenosphere is divided into platesb. the lithosphere is divided into platesc. the asthenosphere moves over the lithosphered. the asthenosphere is strong and rigid

2. What kind of plate boundary occurs where two plates grind past each other without destroying or producing lithosphere?

3. What type of boundary occurs where two plates move together, causing one plate to descend into the mantle beneath the other plate?

The Birth of a Theory

• Answer the questions on the worksheet while you watch a video about Continental Drift and Plate Tectonics.

• Earth Revealed

Warm Up, Week 6, 9/27turn in your warm-ups from last week

1. List the 4 evidences used by Wegner to support Continental Drift theory.

2. In Plate tectonics, what is divided into plates?

3. List the three types of plate boundaries.

Objectives

• I will be able to compare and contrast the actions at the three different plate boundaries.

• I will be able to give geographic examples of the different plate boundaries.

Key Points – Day 3• A divergent boundary at two oceanic plates can result in a rift

boundary.• New ocean crust is formed at divergent boundaries• An example of a divergent plate boundary on continental lithosphere

would be the East African Rift Valley.• A geographic example of a transform fault boundary is the San

Andreas Fault in CA.• Volcanic island arcs are associated with a convergent oceanic-oceanic

boundary.• An Oceanic-Continental convergent boundary forms a subduction

zone.• A subduction zone is when the oceanic lithosphere is forced

underneath the continental lithosphere when they collide.

Actions at Plate Boundaries

• Remember, there are three types of plate boundaries…

• Explain what each of these mean in your own words.

Actions at Plate Boundaries

• At every type of plate boundary, actions are happening that shape our planet.

• Let’s take a closer look and explore what happens at each of the plate boundaries.

Divergent boundaries

• A divergent boundary at two oceanic plates can result in a rift boundary.

• New ocean crust is formed at divergent boundaries.

• The action of two plates moving apart on the ocean floor is called seafloor spreading.

• Seafloor spreading is the process by which plate tectonics produces new oceanic lithosphere.

Spreading Center of Divergent Boundaries

Divergent boundaries

• When plates move apart on a continent, the landmass can split into two or more smaller segments.

• These are called Continental Rifts.• An example of a divergent plate boundary on

continental lithosphere would be the East African Rift Valley.

East African Rift Valley

Convergent boundaries

• There are two types of plates:1. Continental Plate – a plate of the lithosphere

located on land.– A continental plate is usually less dense and

warmer than an oceanic plate.

2. Oceanic Plate – a plate of the lithosphere located on the ocean floor.– An oceanic plate is generally cooler and more

dense than a continental plate.

Convergent Boundaries

9.3 Actions at Plate Boundaries

A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.

• Denser oceanic slab sinks into the asthenosphere. Oceanic-Continental

• Pockets of magma develop and rise.• Continental volcanic arcs form in part by

volcanic activity caused by the subduction of oceanic lithosphere beneath a continent.

• Examples include the Andes, Cascades, and the Sierra Nevadas.

Oceanic-Continental Convergent Boundary

Convergent Boundaries

9.3 Actions at Plate Boundaries

• Two oceanic slabs converge and one descends beneath the other.

Oceanic-Oceanic

• This kind of boundary often forms volcanoes on the ocean floor.

• Volcanic island arcs form as volcanoes emerge from the sea.

• Examples include the Aleutian, Mariana, and Tonga islands.

Volcanic Arc Island

Oceanic-Oceanic Convergent Boundary

How is the Oceanic-Oceanic boundary different from the Oceanic-Continental boundary?

Convergent Boundaries

9.3 Actions at Plate Boundaries

• When converging plates are on land, two continents collide.

Continental-Continental

• This kind of boundary can produce new mountain ranges, such as the Himalayas.

Continental-Continental Convergent Boundary

Collision of India and Asia

The Himalayas

Transform Fault Boundaries

9.3 Actions at Plate Boundaries

At a transform fault boundary, plates grind past each other without destroying the lithosphere.

Transform faults • Most join two segments of a mid-ocean ridge.

• At the time of formation, they roughly parallel the direction of plate movement.

• They aid the movement of oceanic crustal material.

Transform Fault Boundary

Transform-Fault Boundary• A geographic example of a transform fault

boundary is the San Andreas Fault in CA.

Check in

• What is a geographic example of a transform-fault boundary?

• What is an example of a divergent boundary on continental lithosphere?

• What kind of boundary creates volcanic island arcs?

• Which boundary causes seafloor spreading?

Draw and Describe

1. Draw an oceanic-continental converging boundary. Label the drawing with the following terms: (pg. 261)

Oceanic Crust Trench Continental volcanic arc Continental Crust Lithosphere Asthenosphere Melting Subduction

2. Describe what happens as the continental plate converges with the oceanic plate in paragraph form. The paragraph must be at least 5 sentences in length.

Vocabulary

You may use the rest of the time to work on your vocabulary for chapters 9 and 11.

The vocabulary list is on the Earth Science Website. Download it and save it so you can access it even when you don’t have internet access.

This vocabulary list is due on FRIDAY!

Brownie Ticket 9/27

1. A divergent boundary at two oceanic plates can result in a ____.a. Rift valleyb. volcanic island arcc. Continental volcanic island arcd. Subduction zone

2. New ocean crust is formed at what boundary?3. Which of the following is a geographic example of a

transform fault boundary?A. the East African Rift valleyB. The San Andreas faultC. the Mid-Atlantic RidgeD. The Andes Mountains

Warm-up 9/28/10

1. A divergent boundary at two oceanic plates can result in a ____________________________.

2. New ocean crust is formed at ____________ boundaries.

3. A geographic example of a transform fault boundary is the ________________________________.

4. Volcanic island arcs are associated with a convergent ______________-______________boundary.

5. An Oceanic-Continental convergent boundary forms a ___________________zone.

Objectives

• I will be able to defend the theory of plate tectonics through paleomagnetism, earthquake patterns, ocean drilling, and hot spots

• I will be able to defend the theory of plate tectonics by describing why plates move

Key Points

• According to the property of paleomagnetism iron-rich rocks show the location of the magnetic poles at the time of their formation.

• Strips of alternating magnetic polarities found in rocks in the ocean basins provide evidence for seafloor spreading.

• The Hawaiian Islands were formed when the Pacific Plate moved over a hot spot.

• The age of seafloor sediments increase with increasing distance from the ocean ridge.

• The thermal convection that drives plate motion is caused by subduction.

Evidences for plate tectonics

• When scientists came up with the theory of plate tectonics they needed to find EVIDENCE to prove what was really happening.

• Today we will learn about 4 specific pieces of evidence that support the theory of plate motion.

• We will then learn more details about WHY the plates are moving, the most exciting evidence of all.

9.4 Evidence for Plate Tectonics

1. Paleomagnetism •If you have ever used a compass, you have used the earth’s magnetism to find your way.

•Invisible lines of force pass through earth and extend from one pole to the other.

•Certain rocks have iron-rich minerals, and when they form as igneous rock, the magnetic rock forms parallel to earth’s magnetic field. So these magnetized rocks have layers that point towards the poles, just like a compass arrow.

9.4 Evidence for Plate Tectonics

1. Paleomagnetism •According to the property of paleomagnetism iron-rich rocks show the location of the magnetic poles at the time of their formation.

•Rocks formed a long time ago will be pointing to where the poles were at the time of their formation. If the rock is moved, the rock’s layers stay where they were pointing at the time of formation.

9.4 Evidence for Plate Tectonics

1. Paleomagnetism •Strips of alternating magnetic polarities found in rocks in the ocean basins provide evidence for seafloor spreading.

•Geophysicists know that earth’s magnetic field will periodically reverse polarity. The north magnetic pole becomes the south and vice versa.

•The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading and plate tectonics.

Polarity of the Ocean Crust

Paleomagnetism Preserved in Lava Flows

This picture shows how earth’s magnetic field will ____________________ polarity.

How long ago was the last time it was reversed?

______________________

How does this help prove the theory of plate tectonics?______________ ______________________ ______________________

9.4 Evidence for Plate Tectonics

2. Earthquake Patterns

• Scientists found a close link between earthquakes and ocean trenches.

• Earthquakes occur in a pattern near plate boundaries (caused by plates rubbing together)

• Deep focus earthquakes (originate deep underground) are not found near ocean trenches• The lithosphere MELTS so there are no

earthquakes from the plates rubbing together.

9.4 Evidence for Plate Tectonics

3. Ocean Drilling• The data on the ages of seafloor sediment

confirmed what the seafloor spreading hypothesis predicted.

• The age of seafloor sediments increase with increasing distance from the ocean ridge.

• The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.

9.4 Evidence for Plate Tectonics

4. Hot Spots• A hot spot is a concentration of heat in the

mantle capable of producing magma, which rises to Earth’s surface;

• The Hawaiian Islands were formed when the Pacific Plate moved over a hot spot.

• Hot spot evidence supports that the plates move over the Earth’s surface.

Hot Spot

Causes of Plate Motion

9.5 Mechanisms of Plate Motion

Convection occurring in the mantle is the basic driving force for plate movement.

• The thermal convection that drives plate motion is caused by subduction.

Defending a Theory…How would you defend the theory of plate

tectonics?

Pretend you are a scientist in the 1960s. You have been asked to talk at a convention about the new theory of plate tectonics. You have some strong evidence to support your case. You also believe that the theory of plate tectonics is better than the theory of continental drift because you can explain WHY the plates move.

Defending a theoryYou and a partner will prepare a presentation to be given in 15 minutes. Your presentation must include the following:

1. List the 3 pieces of evidence and DESCRIBE at least 3 of them to support the theory of Plate Tectonics. Use your own words.

2. Explain WHY the plates move in your own words.

Presentations must be written out to be handed to the teacher after you give the presentation. Both partners in the group must say at least 2 important points during the presentation.

Exit Slip 9/28/10

1. According to the property of ______________ iron-rich rocks show the location of the magnetic poles at the time of their formation.

2. Strips of alternating magnetic polarities found in rocks in the ocean basins provide evidence for _____________ _______________.

3. The Hawaiian Islands were formed when ___________________________________________.

4. The age of seafloor sediments _______________ with increasing distance from the ocean ridge.

5. The thermal convection that drives plate motion is caused by __________________.

Plate Tectonics Lab

PURPOSE: to understand plate tectonics as the mechanism for the formation of earth’s geologic features.

Plate Tectonics Lab

1. Cut out and assemble the puzzle of earth’s tectonic plates.

2. Label the 7 major plates and 5 smaller plates. Use page 256 as a guide.

3. Color each major plate a different color. 4. Put a star over Haiti and Chile to indicate

sites of recent earthquake activity.

Plate Tectonics Lab5. Indicate convergent boundaries. Label them with a

“C”.6. Indicate divergent boundaries. Label them with a

“D”.7. Indicate transform-fault boundaries. Label them

with a “T”.8. Answer the following question on the back of your

paper:a. What geologic events are associated with convergent

boundaries? Divergent? Transform-fault?b. Write a 5 sentence paragraph explaining how plate

motion impacts the earth.