Transcript Shake, Rattle, and Roll the Earth

Shake, Rattle, and Roll the
Earth
Plate Tectonics, Volcanoes, and
Earthquakes
1. Crust
A Review of the Earth’s
Interior
– 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 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 floor
creation
- 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…
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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