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Plate Tectonics
Earth's Formation
The Earth is thought to have been formed about 4.6 billion years ago by collisions in the giant
disc-shaped cloud of material that also formed the Sun. Gravity slowly gathered this gas and dust
together into clumps that became asteroids and small early planets called planetesimals.…

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Moho ­ Zone that separates the Earth's crust from the asthenosphere.
Discovered in 1909 by Andrija Mohorovicic.
Tectonic plates are slabs of lithosphere that can move around because the part of the mantle
directly below is much weaker.
The word "discontinuity" is used for a surface at which seismic waves…

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As magma erupts from mid-ocean ridges, magnetic minerals in molten rock align
themselves with the direction of the Earth's magnetic field.
Magnetic minerals are aligned opposite to magnetic minerals deposited in reverse polarity.
Creates series of Alternating Magnetic stripes along the sea floor.
Crust is older the further away from…

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o This uplifting of the ocean floor occurs when convection currents rise in the mantle
beneath the oceanic crust and create magma where two tectonic plates meet at a
divergent boundary.
o Hotter expanded crust forms a ridge.
o The central part of the ridge may feature a valley where…

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o This feature might widen still further and become submerged by the sea.
o To the north two rifts have widened in to the Red Sea and the Gulf of Arabia.
o Rifting has continued and new ocean floor is forming between Africa and Arabia.
East African Rift valley formed…

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o Continental are of lower density than the Asthenosphere
beneath them, their buoyant nature cause them not to
o They collide with each other and simply become uplifted
and buckle to form fold mountains i.e. Himalayas.
o Erosion and weathering reduce height of mountains, but
isotactic lift in some…

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Another is a harmonic tremor, which is steady movement of magma, deep in the mantle.
There's a strong relationship between earthquakes, volcanic activity and plate tectonic theory. 95%
of the world's earthquakes and most volcanoes are located along plate margins

Vulcanicity Exceptions to plate margins
Hot spots create Volcanoes near…


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