Warm Up1. What is a property of magnetism?

2. What does a magnet produce?

3. What does magnetic forces attract?

4. What causes Earth’s magnetic field?

5. What is reversed polarity?

6. What is special about the minerals in basaltic magma?

7. Are alternating bands of normal and reversed polarity identical on both sides of a mid ocean ridge?

8. Describe how spreading pulls oceanic crust and creates the alternating bands of normal and reversed polarity:

9. What mechanism drives plate tectonics?

Paleomagnetism

• What generates heat in Earth’s core?

– heat from when the planet formed

– pressure

– heat from the decay of radioactive elements.

• How does a compass work?

Plate Tectonics

Plate Tectonics

• Evidence supporting continental drift and sea-floor spreading lead to the development of a new theory: Plate Tectonics

• The theory of plate tectonics explains:

– Why and how large pieces of the lithosphere, called plates, move and change shape

– Studies the formation of features in the earth’s crust

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Plate Tectonics• Layers involved in Plate Tectonics

– Lithosphere• Thin outer shell of the earth• Consists of crust (oceanic and continental) and rigid

upper mantle• Broken into plates that ‘ride’ on the ‘plastic’ (aka

squishy) asthenosphere

Plate Tectonics

• Asthenosphere

– Ductile rock

• Solid rock that is under great pressure and flows

Plate Tectonics• There are 15 major plates

• Plates carry oceans and continents

• The boundaries of the plates don’t always match the outline of the continents

Plate Tectonics• How do scientists know where plate

boundaries are?

– Earthquakes:

• When plates suddenly shift it generates and earthquake

• Frequent earthquakes in a zone help identify a plate boundary

Plate Tectonics

• Volcanoes

- Volcanic zones also help identify a plate boundary

• Pacific ring of fire• Zone of active

volcanoes and earthquakes around the Pacific

• Form when a denser plate dives beneath a less dense plate and starts to melt

Plate Boundaries

• The way plates move determines how the Earth’s surface is affected

– Some boundaries create mountains

– Other’s create rifts or small valley’s

• Three types of plate boundaries

– Divergent boundaries

– Convergent boundaries

– Transform boundaries

Divergent Boundary

• Divergent boundary

– Two plates move away from each other

– How is a divergent boundary created?

– Hot plastic rock in the asthenosphere rises

– Pressure decreases rock melts forming magma

– Magma pushes the lithosphere up and out

Divergent Boundary

– Less dense liquid magma pushes up on the lithosphere causing it to crack

– Pushes plates apart forming a rift valley

– Magma oozes out of the rift

– Comes in contact with cold ocean water and forms new oceanic crust

– Most divergent boundaries are found along the ocean floor but can form where continents diverge too

– check it out

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Did life begin at MOR’s?

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Convergent Boundary

• Convergent boundaries form where two plates collide

• Lithosphere is destroyed at convergent plate boundaries

• Three types of convergent boundaries

– Ocean-continent collision

– Continent-continent collision

– Ocean-ocean collision

Ocean-Continent collision

• One plate sinking beneath another is called subduction

• Ocean-Continent collision

– Oceanic crust (denser) subductsbelow the continental crust (less dense)

– Subduction zone

• Where one plate sinks under another

Ocean-Continent Subduction Zones

• Subduction Zones

– The denser oceanic plate is shoved under the lessdense continental plate

– A trench or depression is created where the plate is subducting

Ocean-Continent Subduction Zone

– Water is subducted along with the plate lowering the melting temperature of the rock

– Oceanic lithosphere melts and becomes less dense

– Floats up, through the continental crust creating volcanoes

• Example Mt. St. Helens, Shasta, Reiner

Draw this on your plate boundaries worksheet

Oceanic-Oceanic plate collision

• Oceanic-oceanic collision

– The older, colder, denser oceanic plate will subductunder a younger, warmer, less dense oceanic plate

– A deep ocean trench forms where two oceanic plates collide

Oceanic-Oceanic Collision

– Oceanic water is subducted along with the oceanic plate

– This fluid causes mantle rock to melt, forming magma

– Magma, being less dense, forces it’s way to the ocean floor forming an island arc

– An island arc is a chain of volcanic islands

• Example Japan

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Continent-Continent plate collision

• Continent-continent collision

– Both have the same density

– Neither subducts

• Something has to happen when two continents collide.

– Plate boundaries begin to crumple

– Uplift of the crust

– Mountains form

– check it out

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Transform Boundaries

• Transform boundaries

– Two types

• Between two continental plates– Strike slip fault

• Between two oceanic plates– Transform fault

Transform Boundaries

• Continental transform boundaries

– Two plates slide past one another

• Strike slip faults

– Edges of plate boundaries don’t slide past one another smoothly

– Edges get ‘stuck’ building a lot of tension until one plate slips

– The slip generates large magnitude earthquakes

• Example San Andreas Fault

• check it out

Transform Boundaries

• Oceanic transform boundaries

– Occur along mid-ocean ridges

– Transform faults end abruptly and are connected on both ends to other faults, ridges, or subduction zones.

– Form a series of zigzagsaccommodating seafloor spreading

– check it out

Draw this in the left margin

Rap

• Yes…as in rap song…just for you

– HIT IT!

Causes of Plate Motion• Convection!!!!!

• Energy in the core and radioactivity in the mantle heats the mantle rock

• Hot mantle rock rises, cooler denser material sinks

Causes of Plate Motion• Ridge Push and Slab

Pull

• As the material convects it drags the overlying plates with it

• Ridge push

– New oceanic floorcreated at a mid-ocean ridge cools, sinks and ‘pushes’ the plate awayfrom the rift

Causes of Plate Motion• Slab Pull

– As one plate subducts (sinks), it pulls the rest of the plate along with it

– This force is called slab pull

– check it out

Summary-Causes of Plate Motion

• Three mechanisms cause plate motion:

1. Drag on the bottom of the lithosphere from convection

2. Ridge Push from magma rising at divergentboundaries (mid-ocean ridges), cools and becomes more dense pushing the plate away from the rift

3. Slab Pull from one subducing plate ‘pulling’ the rest of the plate behind it as it sinks into the mantle

– Earth’s plates constantly move