The Structure of the Earth
Depth Temperature Composition
Inner Core 1250km thick 5500C-6200C Solid Iron and Nickel
Outer Core 2200km thick 3800C-5500C Liquid Iron and Nickel
Mantle 2900km thick 1000C- 3800C Soft semi-molten rock made of rocks . rich in iron and magnesium
Crust 6-80km thick Cool temps-1000C A hard outer shell made from manily . . . basalt and granite
Continental VS Oceanic Crust
- Younger (200 Million Years)
- Thiner (6-10km)
- Can Sink
- Can be renewed or destroyed
- Mainly made of basalt
- Older (1500 Million Years)
- Thicker (25-80km)
- Less Dense
- Cannot Sink
- Can't be renewed or destroyed
- Mainly made of granite
Destructive Plate Boundaries
An oceanic and continental plate collide.
The oceanic plate is denser than the continental plate so therefore it sinks underneath the continental plate - this is called subduction.
As the oceanic crust sinks down into the mantle it melts- forming magma.
As energy builds up the magma may force its way through the continentalcrust and explode as a volcano.
Friction may cause an earthquake.
Constructive Plate Boundaries
Plates are moving apart.
This allows magma from the mantle to rise up to the earths surface and construct new crust.
This can cause volcanoes and earthquakes.
Conservative Plate Boundaries
The final type of common plate margin is the conservative margin. Here the plates slidepast each other, either in opposite directions or at different speeds in the same direction. The sliding motion often causes the plates to get stuck due to the rough nature of the rock. This leads to a build up of pressure, which when released often causes very powerful earthquakes
The plate tectonics that make up the Earth’s crust are not stationery lumps of rock, they are continually moving at around 2-3cm per year. They ‘float’ on the magma beneath them in the mantle, which acts like a conveyor belt for the plates due to the convection currents that occur within the molten rock.
At the surface, the plates are dragged in different directions depending on the direction the convection currents are flowing in.The heat from the core causes the mantle to be heated at its base. The hot rock rises gradually towards the crust. As it rises, it moves further away from its heat source at the core and starts to cool down.
When it reaches the crust, it is forced out sideways because it cannot easily pass through the solid rock above it. It continues to cool and as it cools, it begins to sink back down towards the core. As it reaches the solid outer core, it is again forced sideways because it cannot pass through the solid iron/nickel layer and at the same time it is heated up once again and rises to the surface. This process of heating, rising, cooling and sinking forms currents within the magma called convection currents.
How are fold mountains formed?
- There were long periods of quiet between earth movements during which sedimentary rocks thousands of meters thick, formed in huge depressions called geosycnclines.
- Rivers carried sediments and deposited them into the depressions. Over millions of years the sediments were compressed into sedimentary rocks such as sandstone and limestone.
- These sediementary rocks were then forced upwards into a series of folds by the movement of the tectionic plates.
Fold mountains are found in linear patterns along plate margins where two plates are moving towards each other. This can be either at destructive margins or a collision margin. An example are The Andes Mountains found on the West coast of South America where the Nazca plate is being subducted beneath the South American Plate.
How are ocean trenches formed?
They occur on destructive plate boundaries which move towards each other. The convection surrents moves ther plates towards each other. As the oceanic plate is subducted, it is dragged under the continental. At the same time, the continetal plate is also dragged under a little. This creates a deep ocean trench.
There are two types of folds; Simple Folds ( Anticline and Syncline) and Overfolds.
- Composite volcanoes are formed at destructive margins (move towards each other).
- The oceanic plate is heavier and subducted under the