Structure of the Earth (Edexcel GCSE Geography B)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Structure of the Earth
The Structure of the Earth
The Earth is composed of a number of layers
Inner core: About 1400km in diameter, a solid and dense layer composed of iron and nickel with temperatures of about 5000 - 6000°C
Outer core: About 2100km thick, a semi-molten metal layer with temperatures between about 4000-6000°C
Mantle: About 2900km thick, a semi-molten layer which is less dense than the outer core this is split into two parts
Asthenosphere
Lower mantle
Lithosphere: The thickness varies, and is made up of two types of crust together with the rigid upper part of the mantle.
The two types of crust are:
Oceanic
Continental
Crust
There are two types of crust and they are part of the lithosphere:
The oceanic crust is thinner (5-10km) but heavier, denser and is composed mainly of basalt
The Continental crust is thicker (25-100km) but is older, denser and is composed mainly of granite
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
Mantle
The mantle is composed of the:
Upper mantle which has two layers
The rigid upper layer which is part of the lithosphere
The Asthenosphere which is partially molten plastic type layer which moves under high pressure and is between 35-250km
Lower mantle which is solid and the largest of the Earth's layers (2900km)
Worked Example
Study Figure 1,
Identify which one of the following describes the outer core.
(1 mark)
| A. a liquid layer of 2 200km in thickness |
| B. a solid layer with temperature 5000oC |
| C. a layer of molten and partly solid rock |
| D. a solid layer of 1 300km in thickness |
Answer
A - a liquid layer of 2200km in thickness
Convection Currents
The heat within the Earth (geothermal) which is estimated to reach up to between 5-6000oC is generated by radioactive decay
Heat rises from the Earth's core and creates convection currents in the mantle - the tectonic plates which make up the crust (lithosphere) move on top of the semi-molten mantle below
Current theory is called slab pull theory
This suggests that in addition to the convection currents, plate movement is a result of the weight of the denser oceanic plates subducting and dragging the rest of the plate along
Mantle plumes
Within the mantle there are also mantle plumes which are upwellings of superheated rock
These can lead to either:
Divergent plate boundaries
Hot spots located at random points on a tectonic plate
Worked Example
Explain one cause of tectonic plate movement.
(3 marks)
Answer
Convection currents cause plate movement (1) These currents are generated by heat from the core (1) and push/pull/drag the overlying plates (1).
Heat rising and falling in the mantle (1) creates convection currents (1) which are generated by radioactive decay in the core (1).
Convection currents (1) caused by the radioactive decay of elements in the core (1) push/pulls/drags the tectonic plate (1).
Ridge push can cause plate movement (1). Newly formed plates at ocean ridges have high elevation (1) which pushes away the plate further from the oceanic ridge (1).
Slab pull causes the movement of plates (1) denser plates sinking at subduction zones (1) pull the rest of the plate along with it (1).
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