what is the internal structure of the earth?
crust, lithosphere, mantle and core
what are the properties of the crust?
- thinnest layer
- lighter rocks
- solid; rigid and brittle
what are the properties of the lithosphere?
high temperature and pressure, floats on asthenosphere, rigid & brittle
what are the properties of the mantle?
2900km thick, mostly solid rock that flows under high temperature + pressure
what are the properties of the inner core?
1400km thick, solid because of extreme pressure
what are the properties of the outer core?
liquid, 2100km thick, temperature of 3000 to 5000 degrees celsius
what are the properties of the core?
centre of earth, mostly iron + nickel and very dense
why do plate tectonics move?
- convection currents
- slab-pull (oceanic plates)
- materials in the mantle intensely heated by core –> mantle material expands –> rises and spreads out beneath plates
- causes plates to be dragged along and move away from each other
- hot mantle cools and sinks, pulling plates along
- sinking mantle material heats up against and process repeats
what are the different plate boundaries
transform: slide past each other
divergent: move away from each other
convergent: move towards each other
what is o-o plate divergence?
- sea-floor spreading –> magma rises to form new seafloor between the plates as they move apart
- lava flows out onto the sea-floor –> cools and solidifies
- forms mid-oceanic ridge
- newly formed rocks: closest to mid-oceanic ridge
- i.e. mid-atlantic ridge in the middle of atlantic ocean –> formed when north american plate and eurasian plate diverged
what is c-c plate divergence
- more or less the same concept as oceanic-oceanic (just without sea-floor spreading, magma still rises etc.)
- rift valley is formed
- i.e. east african rift valley system: nubian boundary of african plate moving away from somalian boundary of african plate
what is o-o plate convergence?
- denser plate subducts under the other less dense plate
- ** SUBDUCTION ZONE
- depression in the sea-floor: oceanic trench
- concurrently, denser subducting plate causes mantle material above it to melt –> forms magma
- magma rises through crust to form volcanoes
- i.e. pacific plate converging with philippine plate –> pacific plate subducts beneath the philippine plate, forming the mariana trench and mariana islands
what is c-c plate convergence?
- collide and push against one another; resist subduction because both plates are too thick and buoyant
- plates break and slide along fractures in the crust
- layers or rock on the upper part of the crust –> compressed together –> fold upwards/sideways –> forms fold mountains
- i.e. indian plate + eurasian plate: formation of the himalayas, the tallest mountain range in the world
what is o-c plate convergence?
denser oceanic plate subducts under less dense
what is o-c plate convergence?
- denser oceanic plate subducts under less dense continental plate
- oceanic trench is then formed at the subduction zone
- fold mountains are formed on the continental plate
- active volcanoes are formed on the continental plate when magma below the crust rises to the surface
- earthquakes may occur on continental plate
- i.e. sumatra-austrlian plate subducts under a section of eurasian plate; forming the sunda trench
what are transform plate boundaries?
- slide past each other
- formation of a transform fault
- tremendous stress builds up –> released in the form of violent earthquakes
- i.e. san andreas fault between pacific plate and north american plate
- 1906: earthquake in san francisco, southern california @ san andreas fault
- caused a few hundred kilometres of north american plate to move an averyage of 2.5m (at one point almost 7m) in less than one minute
