Structure of the Earth
- Four main layers form the structure of the Earth:
- Inner core: This layer is about 1400km in diameter. It is a solid and dense layer composed of iron and nickel with temperatures of about 5500°C
- Outer core: The outer core is about 2100km thick, a semi-molten metal layer with temperatures between about 5000-5500°C
- Mantle: About 2900km thick, a semi-molten layer which is less dense than the outer core
- Crust: Made up of two types of crust (continental and oceanic), the thickness varies
Structure of the Earth Diagram
Structure of the Earth
Crust
- There are two types of crust:
- The oceanic crust is thinner (5-10km) but heavier and denser
- The continental crust is thicker (25-90km) but is older and lighter
- Oceanic crust is continually being created and destroyed as a result of plate movement
- This happens because the oceanic crust is denser and so subducts under the continental crust
- As a result continental crust is much older than oceanic crust because it isn't destroyed
Plate tectonics
- The crust is broken into a number of tectonic plates
Distribution of Plate Boundaries Map
Distribution of tectonic plates
- The tectonic plates move on top of the semi-molten mantle below
- Tectonic theory once stated the movement of the plates was the result of convection currents in the mantle
- Current theory is called ridge push and slab pull theory which suggests that the movement is caused by:
- Ridge push - the new crust forming at the constructive boundary which then pushes the older crust away
- Slab pull - the weight of the denser oceanic plates subducting and dragging the rest of the plate along
- Current theory is called ridge push and slab pull theory which suggests that the movement is caused by:
Diagram of Ridge Push and Slab Pull
Convection currents, ridge push and slab pull
- A plate boundary or margin is where two plates meet