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Contents 1 Plate Tectonics and Continental Drift 1.1 The Plate Tectonic Theory 1.2 The History of Continental Drift 1.3 Earthquakes 1.4 Plate Interactions 1.5 Comments

Plate Tectonics and Continental Drift

The Earth's crust is broken up into huge slabs of rock. These slabs of rock are known as tectonic plates. There are seven major, and twelve small plates. Oceanic plates are 5km-10km thick whereas continental plates are bigger at around 25-90km in thickness. Basaltic oceanic plates are made from denser rock, than granitic continetal plates.

The Plate Tectonic Theory

• The earth's crust is divided into separate parts called tectonic plates.
• These plates float on the partially molten rocks of the upper mantle.
• The plates move due to convection cells in the mantle.
• Margins are the areas between the tectonic plates. Margins of converging plates are called destructive margins while margins of diverging plates are called constructive margins. Margins where the plates slide against each other are called conservative margins.
• Plates can be oceanic or continental. When an oceanic plate meets a continental plate, it's drawn beneath the margin of the continental plate and the rocks of the oceanic plate go into the mantle. When a continental plate meets another continental plate, folding may occur and fold mountains created.

The History of Continental Drift

• Continents drift due to the movement of the tectonic plates.
• Originally, there was one large continent called Pangea surrounded by a sea called Panthalassa. It is believed Pangea was centered around present day Africa. ==Tectonic Plates==

Earthquakes

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Energy can be released due to a number of reasons, such as a thrust/strike-slip fault, or when two plates elastically deform as they slide past one another, building up elastic potential energy up until the point where they return back to their original, undeformed shape upon release of this energy (to picture this, slide your hands past each other, applying as much friction as possible. After enough movement your hands will release quickly)

Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes.

Plate Interactions

Each of our Earth's tectonic plates move, albeit only a couple of centimetres per year at most. Scientific studies have failed to experimentally confirm the primary driving force behind tectonic plate movement, but current theories include movement due to convectional currents, slab pulls and ridge pushing.

Because plates are essentially a 'puzzle' and move, plates interact with one another. Generally we classify plate boundaries as conservative, constructive or destructive. We call boundaries conservative when Earth's crust is 'conserved', constructive when new crust forms and destructive when crust is 'destroyed'.

Plate boundaries can also be classified based on the specific processes going on at the particular boundary. For example, we have subduction zones, where an oceanic plate of relatively denser material (as it's colder) sinks below another plate (oceanic OR continental). This type of process is destructive as the friction between the two plates destroys crust. The region where earthquakes most commonly occur at this boundary is called the Wadati-Benioff Zone, where earthquake foci are normally located along the subducting plate. This subducting plate also creates a geological landform: an oceanic trench. Boundaries where two continental plates collide are also destructive and are the cause of the formation of mountain ranges e.g. the Himalaya.

There are also spreading ridges, where two oceanic plates are moving away from one another, allowing magma to rise from the earth and eventually cool to create new crust. This process is constructive, and creates a geological land form called an oceanic ridge.

Finally we have strike-slip boundaries where two plates slide past one another but generally conserve the crust as a whole (i.e. a conservative process). These boundaries do not generally have a distinct geological land form, however, it is generally quite visible in the civil and agricultural landscape (e.g. fences and roads). Some other distinct features are large cracks and joints in the rock.

• Pangea split into two other continents. The northern continent was Laurasia and the southern continent Gondwanaland. Between the two wad a sea called Tethys.
• Gondwanaland then split into the present continents.

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