1.2

• list the layers of the earth, starting from the middle?

  inner core

  outer core

  lower mantle

  upper mantle

  lithosphere
• describe the inner core?

  made up of iron and nickel

  hot due to radioactive decay of elements such as uranium

  high pressure therefore iron and nickel are solid
• describe the outer core?

  made up of iron and nickel

  lower pressure therefore iron and nickel are liquid = atoms can move = creates the earth's magnetic field
• describe the mantle?

  thickest layer

  mostly made of silicon and oxygen

  there is a geothermal gradient in the mantle - highest temperatures nearest the core
• describe the lower mantle?

  rigid due to pressure being exerted on it from the core

  rocks here have a degree of plasticity, meaning they can reshape under stress
• describe the upper mantle?

  known as the asthenosphere

  semi-molten so can flow - causing tectonic plates to move

  cooler temp than lower mantle so rocks tend to be weaker and are more likely to break apart under stress --> the focus of earthquakes is found here
• what is the lithosphere?

  the crust and the very top of the mantle
• what are the two types of crust?

  continental and oceanic
• describe continental crust?

  thicker than oceanic (30 to 70 km thick) but less dense

  mostly made of granite
• describe oceanic crust?

  thinner than continental ( 6 to 10 km thick) but more dense

  mostly made up of basalt
• what did scientists used to think caused tectonic movement?

  convection currents
• explain how convection currents move tectonic plates?

  the earth's core emits heat which heats the mantle causing it to become less dense and rise

  once the rock reaches the upper mantle, it cools, becomes denser and sinks

  this current triggers the movement of tectonic plates
• which type of plate boundary does the rising arm of a convection current cause?

  convergent
• what type of plate boundary does the falling arm of a convection current cause?

  divergent
• what do convection currents rely on?

  the geothermal gradient leading to the creation of mantle of varying densities
• what is now the main tectonic theory?

  slab pull
• what is slab pull?

  1)the rising limb of a convection current will make the oceanic crust above it hotter and less dense

  2) the part of the crust furthest from the rising limb will be much cooler and more dense. this means it will be more likely to be forced underneath another plate

  3) the sinking of the plate at one of its edges pulls the rest of the plate in that direction --> slab pull
• what is the subduction zone?

  the point where one tectonic plate is pulled under another

  --> plates with larger subduction zones tend to move the fastest
• slab pull is believed to be the main driver of plate motion, convection currents are too weak to move dense plates
• what is seafloor spreading?

  as tectonic plates diverge, magma rises to fill the gap, this then cools to form new crust, overtime, the new crust is dragged apart and even more new crust forms between it

  when this happens at a plate margin under the sea, the seafloor gets wider --> seafloor spreading
• how are rift valleys formed?

  similar to seafloor spreading but at land margins

  example: East African Rift system
• what landforms does seafloor spreading create?

  mid-ocean ridges - ridges of higher terrain on either side of the margin.

  • high levels of volcanic activity occurs here

  example: Mid-Atlantic ridge where the Eurasian and African plates are moving apart from the North American and South American plates
• what is paleomagnetism?

  the study of the earth's ancient magnetic fields - can be used to date different parts of the crust at a divergent plate boundary
• due to seafloor spreading, the oldest rock is found furthest away from the ridge. magma is made up of iron-rich rocks and these become polarised when they reach the earth's surface. this means it aligns with the earth's poles through magnetism created by the earths core
• how does paleomagnetism give evidence for seafloor spreading?

  the earth's magnetic field changes polarity roughly every 200,000 years. when the polarity changes, the alignment of the iron-rick rocks in the magma will change direction. by studying the crust either side of a divergent boundary, we can see when it was formed ad how quickly the plates are moving apart
• what is ridge push and how does it move tectonic plates?

  The slope created when plates move apart has gravity acting upon it as it is at a higher elevation. Gravity pushes the plates further away, widening the gap (as this movement is influenced by gravity, it is known as gravitational sliding).