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Flashcards in HAZARDS : Plate Tectonics Deck (30)
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Before the development of the plate tectonic theory, how did scientists divide the interior of the Earth?

Into three different sections:

  • Crust
  • Mantle
  • Core


What is the core?

The centre of the Earth, made of dense rocks containing iron and nickel alloys.


Name and explain the two parts of core:

  • Inner - solid ball
  • Outer - semi-molten 

Both contain iron and nickel alloys.


What is the mantle?

The layer around the core, made up of molten and sem-molten silicate rocks.


What are silicate rocks?

Rocks made of lighter elements such as silicon and oxygen.


Describe the differences in the layers of the mantle:

  • Part nearest the core is rigid.
  • Asthenosphere (layer above this) is semi-molten.
  • Very top layer is rigid.


What does semi-molten mean?

The substance can flow.


Describe the layers of the mantle:

  • Nearest the core is quite rigid.
  • Layer above this is semi molten - asthenosphere.
  • Very top is rigid.


What is the asthenosphere?

The highly viscous, mechanically weak and ductile region of the upper mantle of the Earth.

It lies below the lithosphere.


What is the crust?

The outermost layer of the earth.


What does the lithosphere consist of?

The crust and the rigid upper section of the mantle.

It is the section of Earth that is divided into tectonic plates.


What are the two types of crust?

Oceanic and continental.


Compare the thickness of oceanic and continental plates:

Continental crusts are thicker.

Continental = 30-70km.

Oceanic = 6-10 km.


Compare the density of oceanic and continental plates:

Continental plates are lighter.

2.6 compared to 3.0.


What are continental plates composed of?

Continental plates are mainly made of granite, silicon, aluminium and oxygen.



What are oceanic plates composed of?

Mainly basalt. 

Silicon, magnesium and oxygen.



What is the Earth's main source of internal energy?

Where does this energy come from?

Heat from the core and the mantle - the inner core is about 6000°C and the mantle is around 1000-3500°C.

Some of this energy is left over from when Earth formed and some of it comes from radioactive decay of elements such as uranium. 


Draw a labelled diagram of the structure of the Earth:


What is the lithosphere divided into?

Tectonic plates.


What are tectonic plates?

Massive, irregularly shaped slabs of solid rock, generally composed of both continental and oceanic lithosphere.


What is it called when tectonic plates meet?

Plate boundaries or plate margins.


What is the theory of plate tectonics?

States that the Earth’s solid crust is separated into plates that move over the asthenosphere and that oceanic and continental plates come together, spread apart and interact at boundaries all over the planet.


What are the theories about plate movement?

  • Convection currents.
  • Ridge push.
  • Slab pull.


Slab pull

  • Destructive margins, denser crust forced under less dense crust
  • Sinking of the plate edge pulls the rest of the plate towards the boundary


Ridge push

  • Constructive plate margins
  • Magma rises to surface and forms new crust, which is very hot.
  • Heats surrounding rocks, which expand and rise above surface, forming a slope
  • New crust cools and becomes denser
  • Denser rock moves downslope, away from plate margin
  • Puts pressure of tectonic plates = move apart


What is ridge push also known as?

Gravitational sliding


Convection currents

  • Mantle is hottest close to core, so lower parts of asthenosphere heats up, become less dense and slowly rise
  • As they move to tops of asthenosphere, they cool, become more dense and slowly sink
  • These circular movements of semi-molten rock = convection current
  • Create drag on base of tectonic plates, causing them to move


What is thought to be the most dominant process in tectonic theory?

Slab pull


Sea-floor spreading

  • Tectonic plates diverge = magma rises to fill the gap, cools and forms new crust
  • New crust drags apart and more new crust forms
  • Sea floor gets wide


What structures does sea floor spreading create?

Mid-ocean ridges