I-4 Dynamic I-4 Dynamic Planet NotesPlanet Notes

The Earth’s LithosphereThe Earth’s Lithosphere

The boundary between the The boundary between the lithosphere and the asthenosphere is lithosphere and the asthenosphere is a temperature boundarya temperature boundary

Below the boundary the rocks are Below the boundary the rocks are hot enough to flowhot enough to flow

Above the boundary they are cooler Above the boundary they are cooler and rigidand rigid

Two types of lithospheric Two types of lithospheric platesplates

Oceanic crustOceanic crust Continental crustContinental crust

Oceanic CrustOceanic Crust

Thickens as it moves away from the Thickens as it moves away from the hot mid-ocean ridgehot mid-ocean ridge

ThinnerThinner More denseMore dense Newer crustNewer crust

Continental CrustContinental Crust

Less denseLess dense ThickerThicker Older crustOlder crust

Lithospheric platesLithospheric plates

The lithosphere is not one The lithosphere is not one continuous piececontinuous piece

Made of very large pieces as well as Made of very large pieces as well as a lot of smaller piecesa lot of smaller pieces

These pieces are called lithospheric These pieces are called lithospheric platesplates

Plate BoundaryPlate Boundary

Where two plates are in contact with Where two plates are in contact with each othereach other

Plate MovementPlate Movement

3 Types3 Types Plates are in motion relative to one Plates are in motion relative to one

anotheranother

Divergent BoundaryDivergent Boundary

Plates are moving away from each Plates are moving away from each otherother

Mid-ocean ridgesMid-ocean ridges New plate material produced on New plate material produced on

either side of ridgeeither side of ridge

Convergent BoundariesConvergent Boundaries

Plates are moving towards one Plates are moving towards one anotheranother

Transform BoundaryTransform Boundary

Plates slide past one anotherPlates slide past one another Example – the San Andreas FaultExample – the San Andreas Fault The Pacific Plate is moving northwest The Pacific Plate is moving northwest

relative to the North American Platerelative to the North American Plate Transform boundaries are sometimes Transform boundaries are sometimes

called conservative (lithosphere is called conservative (lithosphere is neither created nor destroyed)neither created nor destroyed)

SubductionSubduction

Surface area of the Earth is not Surface area of the Earth is not changingchanging

Must be a place where plates are Must be a place where plates are consumed and createdconsumed and created

Subduction ZoneSubduction Zone

Plate boundaries where one plate dives Plate boundaries where one plate dives underneath another plateunderneath another plate

The down going plate is an oceanic plateThe down going plate is an oceanic plate The plate that stays at the surface can be The plate that stays at the surface can be

an oceanic plate or a continental platean oceanic plate or a continental plate The place where the down going plate The place where the down going plate

bends downward is marked by a deep bends downward is marked by a deep trench on the ocean floortrench on the ocean floor

Earthquakes and volcanoes are very Earthquakes and volcanoes are very commoncommon

Copy DiagramCopy Diagram

Continent-Continent Continent-Continent CollisionCollision

Subduction zones can make an Subduction zones can make an ocean basin close upocean basin close up

Two continents may meet at a Two continents may meet at a subduction zonesubduction zone

Continents are less dense than the Continents are less dense than the mantle, so they do not go down a mantle, so they do not go down a subduction zonesubduction zone

When two continents meet, one of the When two continents meet, one of the continents is pushed horizontally continents is pushed horizontally beneath the other continentbeneath the other continent

The movement eventually stops, when The movement eventually stops, when the force of friction between the the force of friction between the continents becomes large enoughcontinents becomes large enough

Continent-continent collision zones are Continent-continent collision zones are where the continent is the thickestwhere the continent is the thickest

ExampleExample

India is slowly being pushed under India is slowly being pushed under southern Asiasouthern Asia

Produces the Himalayas – the Produces the Himalayas – the highest mountain chainhighest mountain chain

Also produces the Tibetan PlateauAlso produces the Tibetan Plateau

AYR QuestionsAYR Questions

1. What is the difference between crust 1. What is the difference between crust and lithosphere?and lithosphere?

What is the difference between oceanic What is the difference between oceanic crust and the continental crust?crust and the continental crust?

What is the difference between a What is the difference between a subduction zone and a continent-subduction zone and a continent-continent collision zone?continent collision zone?

Why do continents not go down Why do continents not go down subduction zones?subduction zones?

Review and Reflect Review and Reflect QuestionsQuestions

What type of plate boundaries are What type of plate boundaries are found in or along the continental found in or along the continental United States?United States?

Why does the surface of a thicker Why does the surface of a thicker continent stand higher above sea continent stand higher above sea level than the surface of a thinner level than the surface of a thinner continent?continent?

Answers to I-4 AYR Answers to I-4 AYR QuestionsQuestions

1.1. The curst is the outermost shell of the Earth. The curst is the outermost shell of the Earth. The lithosphere consists of the crust and the The lithosphere consists of the crust and the upper, rigid part of the mantle (the part that upper, rigid part of the mantle (the part that does not take part in the mantle convection).does not take part in the mantle convection).

2.2. Continental crust is thicker, less dense, and Continental crust is thicker, less dense, and generally much older than oceanic crust.generally much older than oceanic crust.

3.3. A subduction zone occurs where oceanic A subduction zone occurs where oceanic lithosphere is subducted under another lithosphere is subducted under another oceanic lithospheric plate). A trench forms on oceanic lithospheric plate). A trench forms on the sea floor as one lithospheric plate the sea floor as one lithospheric plate descends below the other.descends below the other.

In a continent-continent collision, In a continent-continent collision, one of the two continental plates one of the two continental plates slides horizontally under the other slides horizontally under the other for some distance. That thickens the for some distance. That thickens the continental crust and forms high continental crust and forms high mountain ranges.mountain ranges.

4. Continents cannot go down 4. Continents cannot go down subduction zones because subduction zones because continental lithosphere is less dense continental lithosphere is less dense than the mantle.than the mantle.