Plate Tectonics Theory
The structure of the Earth
- The Earth is composed of four main layers:
- Inner core: About 1400km in diameter, a solid and dense layer composed of iron and nickel with temperatures of about 5500°C
- Outer core: 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: The thickness varies, and is made up of two types of crust
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, where it is denser and so subducts under the continental crust
- This is why continental crust is much older than oceanic crust, as it isn't destroyed
Plate tectonics
- The crust is broken into a number of tectonic plates
Distribution of the major tectonic plates
- These 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 slab pull theory which suggests that the movement is the result of the weight of the denser oceanic plates subducting and dragging the rest of the plate along
- A plate boundary or margin is where two plates meet