Geography- Restless earth

The earths crust is the surface of the earth. It is a rock layer forming the upper part of the lithosphere. The lithosphere is split into tectonic plates. These plates move slowly-2-5 cm per year- on a layer called the asthenosphere.

There are two types of crust:
Continental crust- Forms the land. Mostly made of granite (igneous rock). Low indensity. On average 30-50km thick.
Oceanic crust- On average 6-8km thick. Denser than Continental crust. Made of basalt (igneous rock).

The movement of the tectonic plates is evidence that there is a layer under the lithosphere. This is called the asthenosphere.

Key words:
Asthenosphere- The top layer of the mantle.
Mantle- Largest of the earths layers by volume. Mostly solid rock.
Lithosphere- The layer covering the earths surface.
Tectonic plates- The earths surface is broken into large peices.

Inside the earth is is hot. Heat from inside the earth is called geothermal ('earth-heat'). The heat is produced by radioactive-decay of elements in the core and the mantle. This raises the core's temperature to over 5000C.
How plates move:
The uranium in the core creates the radioactive-decay in the earths core. This creates geothermal heat. The heat rises and creates convection currents in the mantle, and this causes the tectonic plates to move.

The earth is surrounded by a magnetic field called the magnetosphere. The earths magnetic field is made by the outer core. As liquid iron in the outer core flows, it works like an electrical dynamo. This produces the magnetic field.
You can sometimes see the magnetosphere- The northern lights- when radiation from space hits the magnetosphere and lights up the sky.

Key Words:
Geothermal heat- Heat inside the earth.
Radioactive decay- Atoms release particles from their nuclei and give off heat.

The earths lithosphere is split into 15 large tectonic plates and over 20 small ones. These are like the patches that make up a football.
The plates move slowly on the asthenosphere.
When two plates meet, there is a plate boundary. Most earthquakes and volcanoes are found on a plate boundary. 

There are three types of plate boundary:
Constructive- Formed when two plates move apart.
Destructive- Formed when two plates colide.
Conservative- Formed when two plates slide past each other.

New oceanic crusts forms constantly at constructive plate boundaries.
Old oceanic crust is destroyed by subduction as destructive plate boundaries.

Key Words:
Subduction- Oceanic crust sinks into the mantle at a destructive plate boundary.

Earthquakes and volcanoes occour at plate boundaries. Different plate boundaries produce different tectonic hazards.

Conservatice boundaries.
As plates slide past eachother, friction between them causes earthquakes. These are very rare but very destructive because they are shallow.

Constructive boundaries.
As plates move apart, magma rises up through the gap, It forms lava flows and shallow sided volcanoes. Earthquakes are caused by friction as the plates tear apart. These earthquakes are small and do not cause much damage.

Destructive boundaries.
As plates brush together, the oceanic plate is subducted. Sea water is dragged down with the plate. The water erupts as steam making volcanoes very explosive.