Earth+Systems+Topic

The work we have studied so far is:

1. **Composition of the Geosphere, Atmosphere, Hydrosphere**

The Geosphere is made of: 47% Oxygen 28% Silicon 7.9% Aluminium 4.5% Iron The Hydrosphere is made of: 97% saltwater 3% freshwater

The atmosphere is made of: 78% Nitrogen 21% Oxygen


 * 2. Structure of the Geosphere, Atmosphere, Hydrosphere[[image:800px-Earth-crust-cutaway-english_svg.png width="353" height="298" align="left"]]**






 * 3. Continental drift -Wegeners evidence**

We are collaborating on a page at http://013science.wikispaces.com/Alfred+Wegener to discuss Wegeners evidence.


 * 4. Tectonic plates**

If you plot earthquake and volcano locations onto a world map, the plots form a pattern. This is because on the boundary between tectonic plates, earthquakes and volcanoes happen. There is a diagram below to show the location of the plate boundaries.


 * [[image:800px-Tectonic_plates.png width="498" height="401" align="left" caption="tectonic plates"]]

5. Classifying tectonic plates**

Plates can be classified in the following ways:

a) Convergent - These can be either - //continental collision// (e.g. Himalayas -from the collision of India and Asia) This creates mountain ranges. or //Subduction// (e.g. North Island, NZ) - where oceanic crust moves under continental crust, melts and causes volcanoes to erupt at the surface. There are deep earthquakes above the area of crust which is subducting deep into the crust and shallow ones where the two plates meet. See diagram below:



b) Divergent - Divergent plates are moving apart. They form mid-ocean ridges or volcanic islands. (e.g. Mid-Atlantic ridge, Iceland) Divergent plates release magma from below to form new crust.

c) Transform - These plates are sliding past each other. Stresses build up due to friction and when it is released, earthquakes occur.