The Changing Earth Cognitive Learning Systems, Inc © 2008.

The Changing Earth

Cognitive Learning Systems, Inc © 2008

The Changing EarthSurface and Interior of the Earth


Surface of the EarthIm

ag

e co

urte

sy: http

://ge

olo

gy.w

r.usg

s.go

v/do

cs/usg

snp

s/ind

ex.h

tml


Theory: Continental Drift

In 1912, Alfred Wegener proposed the theory of Continental Drift

The continents as they exist today were not always in the same position.

Used fossil and geologic evidence for his theory

Proposed that 225 million years ago, there was a super-continent called Pangaea that split to form the continents of today

As Pangaea split, the continents drifted to their current position

Ima

ge

cou

rtesy: h

ttp://p

ub

s.usg

s.go

v/gip

/dyn

am

ic/dyn

am

ic.htm

l


Layers of the EarthEarth is composed of several different layers:

CoreMantleCrust

Core Mantle

Crust


Three Main Layers of the EarthCrustouter layer• very thin and rigid• 5 km thick below the surface of the

ocean• 30 km thick beneath the continents• 100 km beneath mountain ranges. • Brittle and can break

Mantle• more dense than the crust• semi-solid rock• 2900 km thick• more iron, magnesium, and calcium

than the crust. • Hotter than the crust because

temperature and pressure increase as the depth inside the earth increases.

Mantle

Crust


Three Main Layers of the Earth

Core• Two times as dense as the mantle• Composed of more iron and nickel than the other layers.• Made of two parts• Outer core which is a 2200 km liquid• 1250 km solid inner core• As Earth rotates the liquid outer core rotates creating the Earth’s

magnetic field.

Inner core

Outer core


Mechanical Layers of Earth

Lithosphere (solid surface)• Top part of mantle is more rigid than lower parts. • In many ways it is similar to the crust• Together the top or upper part of the mantle and the crust can be thought

of as a layer called lithosphere.• About 80 km thick

Imag

e co

urte

sy: h

ttp://

pubs

.usg

s.go

v/gi

p/dy

nam

ic/d

ynam

ic.h

tml


Mechanical Layers of Earth

Asthenosphere (liquid layer)• Thin layer of mantle directly under lithosphere• Made of hot, semi-solid material• Can soften and flow• It acts like a fluid and circulates in currents under the lithosphere• Source of lava, magma and the heating source for hot springs and geysers

Imag

e co

urte

sy: h

ttp://

pubs

.usg

s.go

v/gi

p/dy

nam

ic/d

ynam

ic.h

tml


Check Understanding

1. What was Pangaea?

2. How would you describe the theory of Continental Drift?

3. What is the relationship between the crust, lithosphere, and mantle?


The Changing EarthPlate Tectonics Theory


What Can You Recall?

1. The surface of the Earth has changed over the course of millions of years. Were there always 7 continents and 4 major oceans?

2. What was Pangaea?

3. How would you describe the theory of Continental Drift?

4. What is the relationship between the lithosphere and the asthenosphere?

5. What is the relationship between the crust, lithosphere, and mantle?


Theory: Plate Tectonics (1960’s)

•The lithosphere is composed of plates or sections of lithosphere that float on top of the asthenosphere

•The plates can move because they float on top of the asthenosphere.

•The convection currents or movements of molten rock in the asthenosphere may be the force that starts the movement of the plates.

•The plates can move closer together or farther apart.

Image courtesy: http://pubs.usgs.gov/gip/dynam

ic/dynamic.htm

l


•As plates moved over the history of the Earth, different continents were joined, mountains and trenches were formed, and continents divided.

•The surface of the Earth looked different over the time because of plate tectonics (movements of plates)

Theory: Plate Tectonics (1960’s)Im

age courtesy: http://pubs.usgs.gov/gip/dynamic/dynam

ic.html


Tectonic Plate Boundaries

•Divergent: plates are moving away from each other

•Convergent: plates are moving towards each other.

•Transform: plates are sliding past one another.


ic/dynamic.htm

l


Making and Applying Connections

1. What is shown in the diagram above?A. a tectonic plateB. a gem stoneC interior of the EarthD. layers of the ocean

inner core

outer core

mantle


2. How is the inner core of the Earth like the crust?

A. They are both the same temperature.B. They are both liquids.C. They are both solids.D. They are both the same thickness.

3. The theories of Plate Tectonics and Continental Drift both described

A. layers of the EarthB. how oceans formedC. why the surface of the Earth changesD. types of rocks



4. In the picture above the dotted lines show some boundaries that exist on the surface of the Earth. Which of the following best describes what the boundaries represent.

A. The edges of the continentsB. The widths of the oceansC. The edges of tectonic platesD. The layers of the Earth



ic/dynamic.htm

l


Year Juan de Fuca Plate North American Plate

1 Moved 2 cm toward North American Plate

Moved 2 cm toward Juan de Fuca Plate





5. The table above shows the movement of two plates near the coast of California over 3 years.

What type of boundary exists between the two plates?

A. Divergent boundary

B. Convergent boundary

C. Transform boundary

Juan de Fuca plate

North American Plate




The Changing EarthThe Lithosphere, Asthenosphere and Tectonic Plates

What Can You Recall?

1. The surface of the Earth has changed over the course of millions of years.

a. What were the names of the two major theories that described why the surface of the Earth has

changed over millions of years?

b. What are some similarities and differences between these two theories.

2. What is the relationship between the lithosphere and the asthenosphere and tectonic plates?

3. What type of boundaries exist between tectonic plates?


Understanding how tectonic plates move• Let’s pick a starting point. A section of

lithosphere on one tectonic plate.

• The tectonic plate has continental lithosphere and oceanic lithosphere.

Asthenosphere (pink)

Continental lithosphere(red)

Floating just at or above sea level.

Oceanic lithosphere(orange)

Floating lower, beneath sea level.

Sea level


Continental and Oceanic Lithosphere• Continental lithosphere is composed mostly granite. Granite is type of

igneous rock. It’s density allows it to “float” a few hundred meters above sea level.

• Lithosphere of the ocean basins or floors are composed of different types of igneous rocks. One of which is basalt. They are MORE dense than granite. They still “float” on top of the asthenosphere, but they float about 10 km BELOW sea level.


Composed of granite (igneous rock)


Composed of basalt (igneous rock)

Sea level

Asthenosphere(pink)


Convection Currents

•Heat from the Earth’s core is transferred to the asthenosphere, heating it.

•Warmer molten rock rises to the top layer where is cooled by contact with the lithosphere.

•This cooler, still liquid rock, sinks back down into deeper sections of the asthenosphere and the cycle begins again.

•This creates which is known as convection currents in the asthenosphere.


ic/dynamic.htm

l


The Changing EarthDivergent Boundaries


Rifting: Creating a Divergent Boundary

•Molten rock (magma) moved upward by convection currents can heat the bottom of the lithosphere, melting it.

•Some of the magma cools inside and on the surface of the crust, creating different types of igneous rock.

•As magma pushes upward it put pressure on the crust, cracking it.

Magma rising

Magma rising

Crack in crustCrack in crust



• Magma that squeezes through the crack of the rift produce volcanoes.

• As more cracks develop, the area between the two sides of the crust sinks into the mantle creating a valley. This valley is called a rift.

• This magma creates new crust on the surface of the Earth.

volcano

rift

Magma rising

Magma rising



A rift is an example of a divergent boundary.

Rifts can occur under continental lithosphere and oceanic lithosphere. In both cases volcanoes form and earthquakes can occur.

When rifts occur, the tectonic plate can remain intact with a crack in the middle or it can split in two creating two new tectonic plates.

volcano

rift

Magma rising

Magma rising


Mid-Oceanic Ridges• Rifts that form under the ocean

are call mid-oceanic ridges.

• Mid-oceanic ridges are places in which the upward movement of magma has created a string of rifts.

• Mid-oceanic ridges are divergent boundaries between two tectonic plates.

• Mid-oceanic ridges can extend for hundreds of kilometers.

• The example here is the Mid-Atlantic Ridge. Two different tectonic plates exist on either side of the ridge.


ic/dynamic.htm

l


Mid-Oceanic Ridges

• As more and more magma comes up and cools new basalt igneous rock is formed and ocean floor is created.

• The process of magma rising and spreading continues. After several million years, the two tectonic plates can be separated by thousands of kilometers and the ocean between the tectonic plates expands.


ic/dynamic.htm

l

new ocean floor

Previously created ocean floor

Previously created ocean floor

new ocean floor


Mid-Oceanic RidgesIm

age courtesy: http://pubs.usgs.gov/gip/dynamic/dynam

ic.html

• Iceland is a country that is slowly being divided into two by the Mid-Atlantic Ridge.

• The Mid-Atlantic Ridge runs through Iceland.

• As a result, Iceland is an area of high volcanic and earthquake activity.

• As more and more magma moves up through the Mid-Atlantic ridge, new crust is created and the Eurasian and North American Plates move farther apart.

= volcanoCognitive Learning Systems, Inc © 2008

• Rifts can also occur in continental lithosphere.

• These areas are areas of volcanic and earthquake activity.

• Because these rifts tend to involve isolated spots, the separation of the continent into two tectonic plates may take millions of year.

• One example of a continental rift is the East African Rift.

Continental RiftsIm

age

cour

tesy

: http

://pu

bs.u

sgs.

gov/

gip/

dyna

mic

/dyn

amic

.htm

l


If the pressure on thecrust and thespreading of crustcontinue, scientistspredict that theeastern coast ofAfrica willseparate from the

restof the continent andthe Indian oceanwill move in between the two plates.

The result wouldresult inmaking the east coastof Africa an island.

Continental Rifts

Image courtesy: http://pubs.usgs.gov/gip

/dynamic/dynamic.html

East African Rift


Check Understanding

Mid-oceanic ridges are shown as the pink dashed lines.

1. How many mid-oceanic ridges can you find?

2. What type of boundaries are mid-oceanic ridges?

3.How can mid-oceanic ridges explain how continents move across the Earth?


ic/dynamic.htm

l


The Changing EarthMaking and Applying Connections


Making and Applying Connections1. Earthquakes, formation of volcanoes and rifts are evidence for

which of the following theories:

A. Continental DriftB. Fossil successionC. Rock cycleD. Plate tectonics

2. Which of the layers of the Earth change when tectonic plates move?

A. Inner CoreB. LithosphereC. AsthenosphereD. Outer Core

3. The driving force for movement of tectonic plates is

A. rotation of the outer core of the EarthB. convection currents in the mantleC. generation of waves in the oceanD. cooling of the inner core Cognitive Learning Systems, Inc © 2008

Making and Applying Connections4. A team of scientists has been creating model to show the distance

between two continents on either side of a mid-oceanic ridge over the period of several thousand years. The table below shows the distances. In reviewing the data you realize one of the data points is missing.

Which is the most likely distance the two tectonic plates will move between 3008 and 4008?

A. 20 kmB. 30 kmC. 10 kmD. 60 km

Year Distance between tectonic plates

2008 6000 km

3008 6010 km

4008

5008 6030 km

6008 6040 km



5. Compare the two maps above. The black spots on Map A are areas of frequent earthquakes. Map B shows tectonic plates. Which conclusion could you make from the information on both maps?

A. There is no relationship between tectonic plate boundaries and earthquakes.B. Earthquakes occur only in Africa.C. Earthquakes occur only at divergent boundaries.D. Earthquakes occur at the boundaries of tectonic plates.

Images courtesy: http://pubs.usgs.gov/gip/dynamic/dynamic.html


Making and Applying Connections6. How is continental lithosphere different from oceanic lithosphere?

Asthenosphere (pink)


Floating just at or above sea level.


Floating lower, beneath sea level.

Sea level

A. Continental lithosphere floats on the asthenosphere, oceanic lithosphere does not.B. Continental lithosphere is more dense than oceanic lithosphere.C. Oceanic lithosphere floats on the asthenosphere, continental lithosphere does not.D. Oceanic lithosphere is more dense than continental lithosphere. Cognitive Learning Systems, Inc © 2008

Making and Applying Connections7. Which of the following would be the most likely reason

that tectonic plates float on the asthenosphere?

A. pH of the lithosphere B. Volume of the lithosphereC. Mass of the lithosphereD. Density of the lithosphere

8. Which of the following would best explain why a rift formed in the lithosphere?

A. Magma from the mantle pushed up through the Earth’s crust.B. Magma from the mantle moved downward into the Earth’s core.C. Cracks in the Earth’s crust cause volcanoes.D. Earthquakes produce cracks in the Earth’s crust.


Making and Applying Connections9. Catherine thinks that magma forms different types of rock on land

and under water. To test her idea she should obtain a sample of magma and

A. Expose half of the magma to salt water and half of the magma to fresh water.B. Expose half of the magma to polluted air and half of the magma to clean air.C. Expose half of the magma to salt water and save the other sample of magmaD. Expose half the magma to water and half of the magma to air.


10. There is a divergent boundary between the Indian and African plates. Which of the following will likely happen over the next million

years?

A. Africa and India will move closer togetherB. Africa and India will move farther apartC. The position of Africa and India will be the same.D. Africa will move northward and India will move southward.

divergent boundary



The Changing EarthConvergent and Transform Boundaries


Subduction-Creating a Convergent Boundary

Creation of new ocean crust at mid-oceanic ridges can continue for tens to hundreds of millions of years.

At some point, however, new oceanic crust breaks and begins to move beneath the mantle. This is called subduction.

In the example above, when subduction occurs, the two continents on either side of the mid-oceanic ridge stop moving apart and begin moving back toward one another.

Oceanic crust(lithosphere)

Subducting into mantleunder continental crust

Continental crust(lithosphere)

remains on top of mantle


Convergent Boundaries

One side of the ocean crust is dragged down below the other side.A trench is formed. It can extend 1-2 km below the ocean floor. As the ocean crust slides into the mantle, it begins to melt formingmagma.

Magma rises towards the ocean floor as lava and creates a volcano.Eventually enough lava rises up that an island is formed.

The island is now considered the beginning of the convergentboundary of two different tectonic plates. The example above isoceanic plate /oceanic plate convergence.


ic/dynamic.htm

l



Similar processes occur when the subduction zone is near the edgeof a continent. Volcanoes appear under crust that is above sea level creating higher mountains than seen with island building. This is called oceanic/continentconvergence.

Like divergent boundaries, volcanoes and earthquakes can occur atconvergent boundaries.


ic/dynamic.htm

l



•Imagine an example in which subduction continues until an island and continent meet or two continents on sides of an ocean meet.

•One must slide over the other. Great heat and pressure occur at this area.

•Area that was the trench and contains crust that was underwater is thrust up over the other plate.

•The two plates are now “sutured” together. Subduction and volcanic activity stop.

•The island or one continent has now overridden the other continent forming high mountains.


ic/dynamic.htm

l


Transform Boundaries

Tectonic plates slide past one another

Not usually associated with volcanic activity

Associated with earthquakes.

Shifting of plates can causes openings or fractures in the surface of the Earth.

One of most famous examples: San Andreas Fault in California

Images courtesy: http://pubs.usgs.gov/gip/dynam

ic/dynamic.htm

l Cognitive Learning Systems, Inc © 2008

Check Understanding

1. Look at the diagram above and think about what you learned about the processes of subduction. How can you explain the following findings?

The oldest ocean crust is 200 million years old, but the oldest continental crust is 3 to 4 billion years old.

Image courtesy: http://pubs.usgs.gov/gip/dynamic/dynamic.html


Check Understanding2. Why would sedimentary rock containing ocean fossils

be found in the mountains now existing on land?

3. Which of the following would you not expect to find at a transform boundary?

A. Two tectonic plates B. A volcano C. Earthquakes D. Fractures in the surface of the Earth

4. How are divergent and convergent boundaries different? How are they similar?



The Changing EarthMaking and Applying Connections:

Convergent and Transform Boundaries:


1. Magma comes from which layer of the Earth?

A. CrustB. Inner coreC. Outer coreD. Mantle

2. The theory of plate tectonics involves two layers of the Earth. What are they?

A. Core and mantleB. lithosphere and asthenosphereC. lithosphere and coreD. asthenosphere and core



3. Which of these statements explains what is happening to the tectonic

plates in the diagram above?

A. Magma is rising from the mantle to move the tectonic plates farther apart.

B. Oceanic floor of Tectonic Plate B is being subducted into the mantle below Tectonic Plate A.

C. Magma rising from the mantle is forming new ocean floor next to Tectonic Plate A

D. Oceanic floor of Tectonic Plate A is being subducted into the mantle below Tectonic Plate B.

Tectonic plate A

Tectonic plate B

mantle


4. There is a convergent boundary between the Eurasian and African plates. Which of the following will likely happen over the next

million years?

A. Africa and Europe will move closer togetherB. Africa and Europe will move farther apartC. The position of Africa and India will be the same.D. Africa will move northward and Europe will move southward.


Eurasian Plate

African Plate


Making and Applying Connections5. A team of scientists have been creating a model to show changes in the

distance between a continent and island on either side of subducting plate over the period of several thousand years. The table below shows the distances. In reviewing the data you realize one of the data points is missing.

Which is the most likely distance the two tectonic plates will move between 3008 and 4008?

A. 20 kmB. 30 kmC. 10 kmD. 60 km

Year Distance between island and continent

2008 6000 km

3008 5090 km

4008

5008 5070 km

6008 5060km


Making and Applying Connections6. What happens to the size of an ocean between two continents if

the ocean is part of a convergent boundary?

A. The ocean will remain the same size

B. The ocean will become larger

C. The ocean will become smaller

D. The ocean will become saltier

7. The source of magma at convergent boundaries comes from

A. convection currents in the mantle

B. melting oceanic crust

C. the Earth’s core

D. Volcanoes


Making and Applying Connections 8. The table below shows the density of different types of lithosphere, and

which plate was subducted at different tectonic boundaries. What conclusions can you draw from the information in the table?

A. The more dense lithosphere is always subducted below the less dense lithosphere.

B. Density is not related to plate subduction

C. The density of oceanic and continental lithosphere is the same.

D. Continental lithosphere is more dense than oceanic lithosphere.

Plate Lithosphere type Density

(kg/m-3)

Subduction

A Oceanic 40 Plate A subducted below Plate BB Continental 30

C Continental 25 Plate C subducted below Plate DD oceanic 45



9. The diagram above shows an area called “The Ring of Fire”. The volcanic islands that formed in this area are highlighted. They were most likely created at

A. The edge of a divergent boundary

B. The edge of a transform boundary

C. The edge of a convergent boundary

D. The edge of a biological boundary


ic/dynamic.htm

l


Making and Applying Connections10. Many mountain ranges result from

A. Convergence of two tectonic plates

B. Rifting at divergent boundaries

C. Movement of Earth’s core

D. Earthquakes


The Changing Earth Cognitive Learning Systems, Inc © 2008.

Documents

Transcript of The Changing Earth Cognitive Learning Systems, Inc © 2008.