Composition of the Earth
Earth Layers
 The earth isn’t a solid sphere
 It is made of 4 major layers
- Crust
- Mantle
- Outer core
- Inner core
Crust
 “outer skin”
 Continental crust is
about 70km thick
 Oceanic crust is
about 10 km thick
 (this is why so much
ocean drilling occurs)
Mantle
 About 2900 km thick
 Made of mostly Iron, Silicon and Magnesium
 Asthenosphere is
the upper part of
the mantle
 Very viscous
Outer Core
 Approx 2100 km thick
 Made of molten Iron and Nickel
Inner Core
 Approx 1300 km
radius
 Solid ball of Iron and
Nickel
 Extremely hot
 Stays a solid due to
very high pressure
Quick check
 T/F – all layers are made of solid rock
 T/F – thickest layer is the mantle
 T/F – Inner core is made of liquid Iron
and nickel
 T/F – Outer core is made of silicon and
oxygen
Answers
 F – all layers are made of solid rock
 T – thickest layer is the mantle
 F – Inner core is made of liquid Iron and
nickel
 F – Outer core is made of silicon and
oxygen
Plate Movement
 Caused by convection currents in the
mantle
Definitions
 Trench – steep walled valley where 2
plates meet
 Slab pull – plates subducting pulls the
rest of the plate with it
 Ridge Push – new forming rock pushes
plate away from spreading centre
Definitions
 Spreading Centre – area where plates
move apart from each other
 Rift Valley – a spreading centre that
occurs on land
Types of Movement
Collisions at Plate Boundaries
 Divergent
- Pulling apart
(spreading)
- New rock is often
formed here
Collisions at Plate Boundaries
 Convergent
- Plates come together
- Often subduction occurs (one slides under
the other)
**More on this in a moment**
Collisions at Plate Boundaries
 Transform
- Plates slide past each other
- Produces earthquakes
- Eg. San Andreas Fault
Convergent Boundaries
 There are three different types of
convergent boundaries
 These depend on what type of plates
come together
 Oceanic-continental
 Oceanic-oceanic
 Continental-continental
Oceanic-Continental
 The oceanic plate subducts beneath the
continental plate
 Eg. Coastal BC
 The Juan de Fuca (oceanic) plate
subducts under the North American
(continental) plate
 This causes coastal mountains and land
volcanoes
Oceanic-Oceanic
 One plate will subduct beneath another
 Volcanic activity and possible islands
form
Continental-Continental
 Plates are not likely to subduct
 They push on each other and form
mountains