Shake, Rattle, and Roll the Earth

Plate Tectonics, Volcanoes, and Earthquakes

1. Crust– Solid material– upper portion of lithosphere

2. Asthenosphere– plastic in nature (partly solid, partly liquid, allows it to flow)– lower portion of lithosphere– can flow very slowly with changes in heat

3. Mantle– layer below asthenosphere– more solid material

4. Outer core– liquid iron and nickel layer– less dense than inner core – allows certain seismic (earthquake) waves to pass through

5. Inner core– solid iron and nickel layer– more dense than outer core– blocks seismic (earthquake) waves

A Review of the Earth’s Interior

A quick review of p. 10

• What is the density of the outer core?

• At what temp is the Earth at a depth of 3000 km?

• What is the pressure at the top of the inner core?

The Untold

Tragedies of

Continental

Drift

Theory of Continental Drift

• 1912 – Alfred Wegener proposes the theory

• but has no way to explain how the continents move

• what was his

evidence that

they did?

Wegener’s Evidence• South America and Africa “fit” together

– Pangea – the original supercontinent– movement of plates separated to create the

positions of present day continents– one reason why champosaurs could exist in Canada!– See ESRT page 8-9

• Similar fossils found in Africa and South America– how could that happen?

• Similar rock formations– Granite formations in Europe similar to those in US

Plate Tectonics Proves Wegener Right!

• By the 1960’s - Wegener’s theory finally accepted- mechanism for crustal plate movement found

• Theory of Plate Tectonics– a theory that describes the crust as being composed

of interlocking plates– these plates move above the asthenosphere– they can :

• move toward each other (converging boundaries)• move away from each other (divergent boundaries)• move past each other (transform boundaries)

– Plate tectonics studies the formation and movement of these plates

Proof of Plate Tectonics

• Earthquakes and Volcanoes – occur where plates collide or separate– not random in where they occur

• Magnetism- Earth’s N-S poles periodically “switch”- some igneous rock contains iron- a record of these switches occur in the rock - surrounding the Mid-ocean ridges

(places where new crust is formed)• Heatflow measurements

- measurement are highest at areas of new sea floorcreation

- decreases as one moves away from these points

Plate Movement• The plates move due to the cooling and

heating of the asthenosphere– Hotter material rises, cooler material sinks– Form convection cells– Drives the crustal

plates across the surface of the Earth

What are plates made of?Two (2) types of tectonic crust

1. Continental crust– composed of felsic igneous rock – continental crust rides on top of the plates due to its lower

density– Large amounts of granite

2. Oceanic Crust – Tend to slide under continental crust when they collide – composed of mafic igneous rock – Large amounts of basalt

3. Remember: felsic = low density; mafic = high density

Kinds of Plate Boundaries

Diverging Boundaries• Regions of spreading centers

• Places where two plates are moving apart

• Most have mid ocean ridges

• Ex: Mid Atlantic Ridge– Contains rift valleys - deep valleys where

new material pushes aside older ocean crust– fault lines run perpendicular to the valleys at

various points

• earthquakes occur along the ridge

• Hot magma rises• Pushes on either side of the mid ocean

ridge

Sliding or Transform Boundaries

• Places where plates move past each other

• A fault is a break or crack in the crust where

plates move against each other

• Ex: San Andreas Fault near San Francisco– average rate of movement is 5 cm/yr– some areas have not moved for over a

century – possible earthquake spots

The San Andreas Fault in California

• Side ways movement of the plates• Can get caught – pressure builds – finally

released as…

EARTHQUAKE

Homework for Earth Science• Tuesday Nite HW

– Read pp 295 – 300– Write out and answer questions 1 – 7 p 300

• Wednesday Nite HW– Read pp 301 – 304– Write out and answer questions 1 – 5 p 304

• Thursday Nite HW– Read pp 305 – 308– Write out and answer questions 1 – 5 p 308

• Friday – QUIZ ON Plate Tectonics

Converging Boundaries I – When Plates Collide

• Places where two plates move toward each other

• If both plates carry continents

• A collision boundary forms

• Continental collisions produce mountains, big and small

• - Ex: Himalayan Mtns, Appalachian Mtns

Continent- Continent Collisions

Converging Boundaries II Subduction Zones

• A place where one plate slides under an overriding plate• Deep sea trenches – characteristics of a subduction

zone • Ex: Marianas Trench off Japan

– when two oceanic plates collide– chains of volcanic islands form– Ex: Phillipines

• Occurs when an oceanic plate and a continental plate collide– a mountain chain forms on the continent– some may be volcanic– a trench forms in the ocean

A diagram of a subduction zone