Geography Plate Tectonics Theory

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The Core

The centre of the Earth is the core, split into inner core and outer core:

The inner core is a solid ball containing iron and nickel.

The outer core is semi-molten and also contains iron and nickel.

Temperatures peak around 5,500*C, this heat energy powers the Earth.

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Mantle and Crust

Outside of the core is the Mantle is mostly made up of silicon rocks.

The part nearest the Core is quite rigid.

The layer above this is called the asthenosphere, is semi-molten.

The very top bit of the mantle is rigid and called the lithosphere, where the mantle meets the crust.

This is the rigid top part of the Earth, the crust and upper part of the mantle make up the lithosphere which is responsible for plate movement.

Two types of crust:

Continental - thick and less dense

Oceanic - thin and more dense.

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Tectonic Plates and Convection Currents

The lithosphere is divided into lots of slabs called tectonic plates.

The plates are moving due to convection currents in the asthenosphere.

The places where they meet are called boundaries or plate margins.

The idea that the Earth's lithosphere is made up of many plates that are moved around by convection currents is theory of plate tectonics.

Radioactive decay of elements e.g. Uranium in the mantle and core generates a lot of heat.

When lower parts of the asthenosphere heat up they become less dense and slowly rise.

As they move towards the top of the asthenosphere they cool down, becoming more dense, then slowly sink.

These circular movements of semi-molten rock are called convection currents.

Convection currents in the asthenosphere create drag on the base of the tectonic plates and causes them to move

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Creation of Crust - Sea floor spreading

Rising convection currents move apart at the base lf the lithosphere.

The drag of the convection currents causes the plates above them to move apart as well, creating a constructive plate margin.

Magma rises up and fills the gap created, then cools to form new crust.

Over time the new crust is dragged apart and even more new crust forms between it.

When this happens at a plate margin under the sea, the sea floor gets wider.

This process is called sea floor spreading and creates structures called mid-oceanic ridges (ridges of higher terrain on either side of the margin).

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