Chapter 4Chapter 4

Layers of the EarthLayers of the EarthContinental DriftContinental DriftPlate TectonicsPlate Tectonics

Deformation of Earth’s CrustDeformation of Earth’s Crust

Layers of the EarthLayers of the Earth

CrustCrust Thin, outermost layer of EarthThin, outermost layer of Earth uppermost part of lithosphereuppermost part of lithosphere

MantleMantle Layer of Earth between crust and coreLayer of Earth between crust and core

CoreCore Central, spherical part of Earth below the mantleCentral, spherical part of Earth below the mantle

CrustCrust 5 to 100 km thick5 to 100 km thick thinnest layer of Earththinnest layer of Earth

continental crustcontinental crust similar to granitesimilar to granite

oceanic crust oceanic crust similar to basaltsimilar to basalt

MantleMantle

between crust and corebetween crust and core contains most of Earth’s masscontains most of Earth’s mass

similar to olivinesimilar to olivine large amounts of iron and large amounts of iron and

magnesiummagnesium

Layers of the MantleLayers of the Mantle

LithosphereLithosphere Outermost, rigid layer of Earth Outermost, rigid layer of Earth consists of crust and rigid upper part of mantleconsists of crust and rigid upper part of mantle

AsthenosphereAsthenosphere Soft layer of mantle on which pieces of the lithosphere Soft layer of mantle on which pieces of the lithosphere

movemove

MesosphereMesosphere ““middle sphere”middle sphere” strong, lower part of mantle between asthenosphere and strong, lower part of mantle between asthenosphere and

outer coreouter core

CoreCore

extends from bottom of mantle to extends from bottom of mantle to center of Earthcenter of Earth

slightly larger than Marsslightly larger than Mars

mostly ironmostly iron small amounts of nickelsmall amounts of nickel possibly some sulfur and oxygenpossibly some sulfur and oxygen

Outer CoreOuter Core Inner CoreInner Core

liquid layer of liquid layer of Earth’s core Earth’s core

lies beneath lies beneath mantlemantle

surrounds inner surrounds inner corecore

solid, dense center solid, dense center of Earthof Earth

Tectonic PlateTectonic Plate

a piece of a piece of lithosphere lithosphere

moves around on moves around on top of thetop of the

asthenosphereasthenosphere

How do Scientists know How do Scientists know about the structure of the about the structure of the

inside of the Earth?inside of the Earth?

EarthquakesEarthquakes When an earthquake occurs, When an earthquake occurs,

seismographs measure the difference in seismographs measure the difference in arrival times of seismic waves and record arrival times of seismic waves and record them them

Seismologists use these measurements Seismologists use these measurements to calculate the density and thickness of to calculate the density and thickness of each layereach layer

Continental DriftContinental Drift

The theory that continents can drift The theory that continents can drift apart from one another and have apart from one another and have done so in the pastdone so in the past

PangeaPangea

““all earth”all earth” land mass that existed 245 million years land mass that existed 245 million years

ago made up of all of the continents put ago made up of all of the continents put togethertogether

LaurasiaLaurasia northern half of Pangea; formed 180 million years northern half of Pangea; formed 180 million years

ago when Pangea broke in halfago when Pangea broke in half GondwanaGondwana

southern half of Pangea; formed 180 million years southern half of Pangea; formed 180 million years ago when Pangea broke in halfago when Pangea broke in half

PangeaPangea

On the Sea Floor…On the Sea Floor…

Sea Floor SpreadingSea Floor Spreading The process by which The process by which

new oceanic lithosphere new oceanic lithosphere is created at mid-ocean is created at mid-ocean ridgesridges

older materials are older materials are pulled away from the pulled away from the ridgeridge

Mid-Ocean RidgeMid-Ocean Ridge a long mountain a long mountain

chain that forms on chain that forms on the ocean floor the ocean floor where tectonic where tectonic plates pull apartplates pull apart

usually extends usually extends along the center of along the center of ocean basinsocean basins

Magnetic ReversalsMagnetic Reversals

the process by the process by which the Earth’s which the Earth’s north and south north and south magnetic poles magnetic poles periodically change periodically change placesplaces

Wegener’s TheoryWegener’s Theory

What was Wegener’s theory of continental What was Wegener’s theory of continental drift?drift? The theory that continents can drift apart from The theory that continents can drift apart from

one another and have done so in the pastone another and have done so in the past

Why was Wegener’s theory not accepted Why was Wegener’s theory not accepted at first?at first? Scientists at that time did not understand what Scientists at that time did not understand what

force of nature could move continentsforce of nature could move continents

Sea Floor SpreadingSea Floor SpreadingMid-Ocean RidgesMid-Ocean Ridges

How does sea floor spreading provide a How does sea floor spreading provide a way for continents to move?way for continents to move? It forms new crust in between the places where It forms new crust in between the places where

the spreading takes placethe spreading takes place

How does new oceanic crust form at mid-How does new oceanic crust form at mid-ocean ridges?ocean ridges? As tectonic plates move away from each other, As tectonic plates move away from each other,

the sea floor spreads apart and magma rises to the sea floor spreads apart and magma rises to fill in the gap fill in the gap

This magma cools to form new crustThis magma cools to form new crust

How do magnetic reversals How do magnetic reversals provide evidence for sea-provide evidence for sea-

floor spreading?floor spreading?

The molten rock contains tiny grains of magnetic The molten rock contains tiny grains of magnetic materials which align themselves with Earth’s materials which align themselves with Earth’s current magnetic fieldcurrent magnetic field

They are “set in stone” as the molten rock cools They are “set in stone” as the molten rock cools and solidifiesand solidifies

As the sea-floor continues to spread, these rocks As the sea-floor continues to spread, these rocks are carried away from the spreading centerare carried away from the spreading center

The magnetic fields are found in bands along the The magnetic fields are found in bands along the oceanic crustoceanic crust

Plate TectonicsPlate Tectonics

The theory that states that Earth’s The theory that states that Earth’s lithosphere is divided into tectonic lithosphere is divided into tectonic plates that move around on top of plates that move around on top of the asthenospherethe asthenosphere

Convergent BoundariesConvergent Boundaries

Convergent Convergent BoundaryBoundary The boundary The boundary

between two between two colliding tectonic colliding tectonic platesplates

Subduction ZoneSubduction Zone The region where The region where

an oceanic plate an oceanic plate sinks down into the sinks down into the asthenosphere at a asthenosphere at a convergent convergent boundaryboundary

usually between usually between continental and continental and oceanic platesoceanic plates

Three Types of Three Types of Convergent BoundariesConvergent Boundaries

Continental/Continental CollisionsContinental/Continental Collisions

Continental/Oceanic CollisionsContinental/Oceanic Collisions

Oceanic/Oceanic CollisionsOceanic/Oceanic Collisions

Divergent BoundariesDivergent Boundaries

The boundary between two tectonic The boundary between two tectonic plates that are plates that are moving away moving away from from each othereach other

Transform BoundariesTransform Boundaries

The boundary between two tectonic The boundary between two tectonic plates that are plates that are sliding pastsliding past each each other other horizontallyhorizontally

What are the 3 forces What are the 3 forces thought to move tectonic thought to move tectonic

plates?plates? ConvectionConvection

Slab PullSlab Pull

Ridge PushRidge Push

ConvectionConvection

Hot material from deep with in Earth Hot material from deep with in Earth rises while cooler material near the rises while cooler material near the surface sinkssurface sinks

As warmer material cools, it becomes As warmer material cools, it becomes more dense and sinksmore dense and sinks

The motion drags tectonic plates The motion drags tectonic plates sidewayssideways

ConvectionConvection

Slab PullSlab Pull

oceanic lithosphere is denser than oceanic lithosphere is denser than the asthenospherethe asthenosphere

the edge of the oceanic plate sinks the edge of the oceanic plate sinks pulls the rest of the tectonic plate pulls the rest of the tectonic plate

with itwith it

Ridge PushRidge Push

An oceanic plate sides down the An oceanic plate sides down the lithosphere-asthenosphere boundarylithosphere-asthenosphere boundary

occurs where oceanic lithosphere is occurs where oceanic lithosphere is higherhigher than continental lithosphere than continental lithosphere

Measuring Plate Measuring Plate MovementMovement

using a network of satellites called using a network of satellites called the Global Positioning Systemthe Global Positioning System allows scientists to record the time it allows scientists to record the time it

takes for radio signals from a position on takes for radio signals from a position on Earth to reach the satelliteEarth to reach the satellite

by monitoring changes in this, scientists by monitoring changes in this, scientists can tell how much the plates have can tell how much the plates have movedmoved

StressStress

The amount of force per unit area The amount of force per unit area that is put on a given material that is put on a given material

DeformationDeformation the change in the shape of rock in response the change in the shape of rock in response

to stress appliedto stress applied

CompressionCompression TensionTension The type of stress The type of stress

that occurs when that occurs when an object is an object is squeezedsqueezed

The type of stress The type of stress that occurs when that occurs when forces act to forces act to stretchstretch an object an object

FaultFault

A break in the Earth’s crust along A break in the Earth’s crust along which blocks of the crust slide which blocks of the crust slide relative to one another due to relative to one another due to tectonic forcestectonic forces

Types of FaultsTypes of Faults

Normal FaultNormal Fault a fault in which the hanging wall moves down relative to a fault in which the hanging wall moves down relative to

the footwallthe footwall Reverse FaultReverse Fault

a fault in which the hanging wall moves up relative to a fault in which the hanging wall moves up relative to the footwallthe footwall

Strike-slip FaultStrike-slip Fault a fault in which the two fault blocks move past each a fault in which the two fault blocks move past each

other horizontallyother horizontally

Fault BlockFault Block The blocks of crust on each side of the faultThe blocks of crust on each side of the fault

FoldingFolding

The bending of rock layers due to The bending of rock layers due to stress in the Earth’s cruststress in the Earth’s crust

Types of MountainsTypes of Mountains

Folded Folded

Fault-BlockFault-Block

Volcanic MountainsVolcanic Mountains

Folded MountainsFolded Mountains

form when rock layers are squeezed form when rock layers are squeezed together and pushed upwardtogether and pushed upward

example: example: Appalachian MountainsAppalachian Mountains

Fault Block MountainsFault Block Mountains

where tectonic forces put enough tension where tectonic forces put enough tension on the Earth’s crust, a large number of on the Earth’s crust, a large number of normal faults can resultnormal faults can result

this faulting causes large blocks of Earth’s this faulting causes large blocks of Earth’s crust to drop down relative to other blockcrust to drop down relative to other block

example:example: The Tetons (in western Wyoming)The Tetons (in western Wyoming)

Volcanic MountainsVolcanic Mountains

when molten rock erupts onto the when molten rock erupts onto the Earth’s surfaceEarth’s surface

examples: examples: Ring of FireRing of Fire Mount St. Helen’sMount St. Helen’s