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Hi, currently studying for my AS Geography exam in a couple of weeks.. found some questions to try and get me started. Would like some help to see if I'm going in the right direction with answers...

Outline the characteristics of the Earth's structure.
The crust is the solid, outer layer of Earth. It's between 5 and 80km thick and is fragmented into plates which are either continental or oceanic. The crust can also be known as the lithosphere. The asthenosphere is the uppermost mantle and the crust and it's important in plate tectonics as convection currents occur here. This transitional boundary may also be known as the Mohorovicic Discontinuity. The mantle is made of liquid rock known as magma. At this point there is another boundary known as the Gutenburg Discontinuity. The outer core is liquid and mainly composed of metals. Before the inner core, there is the Lehmann Discontinuity. The inner core is a solid composed of metals and gives off heat.

Describe the types of plates found in the Lithosphere.
All plates are either oceanic or continental. Oceanic plates lie at the bottom of the ocean, where as Continental lie under surface land masses. Oceanic crust is composed of basaltic rocks which are heavier and more dense. It is thinner and younger than it's continental counterpart. Hawaii is an example of Oceanic crust. Continental crust is composed of granitic rocks which are lighter and make it less dense than oceanic crust. It's considerably thicker and older, and an example of Continental crust is North America.

Describe the mechanisms of plate movement.
Tectonic plates are driven by thermal convection currents in the upper mantle. The heat is produced by radioactive decay in the inner core. Ridge push occurs when molten magma rising to the surface at a mid-ocean ridge causes expansion. This produces a slope. The new rock is less dense, however as it cools it becomes more dense and gravity acts upon it. The denser rock slides down the slope. At a divergent margin in the ocean, sea floor spreading can occur. At a subduction boundary, one plate is heavier and denser than the other plate, so it subducts into the mantle. It is heavier than the mantle so continues to sink, pulling the rest of the plate with it. The force of the sinking edge is known as slab pull.

Describe and explain the processes that occur at plate margins.
A divergent margin occurs where plates are moving apart by convection currents. Hot magma rises to fill the gap created when the two plates are separated, creating new crust. It can create landforms such as shield volcanoes, rift valleys, mid ocean ridges and volcanic islands. The North American and Eurasian plate are examples of a divergent margin and they form an ocean ridge known as the Mid-Atlantic ridge.
A convergent margin occurs where plates are moving towards eachother. There are two types of convergent margins – continental and oceanic / continental and continental, and they both behave differently. Where continental and oceanic crust meet, the denser oceanic crust is subducted [forming a subduction zone and oceanic trench]. As it is subducted, the oceanic crust is melted by the high heat and pressure due to friction. This friction and melting allows earthquakes and volancoes to be formed. Other landforms include oceanic trenches, island arcs, and fold mountains. The South American and Nazca plate are an example of a convergent margin and form the Andes. Continental and Continental crust are known as collision margins. Both crust are the same density and thickness so resist subduction and are instead forced upwards to create fold mountains such as the Himalyas. The forces of collision may also cause shallow focus earthquakes. A conservative plate boundary occurs when plates are moving in the same or opposite direction. Friction is occurs but is overcome in a stick-slip motion which is the cause for earthquakes. Crust is neither created nor destroyed so landforms are therefore not created. An example is the Sand Andreas fault, a margin between the Pacific and North American plate.

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