AQA A2 Geography Plate Tectonics: Structure of the Earth

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  • Created on: 22-08-13 20:35
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The internal structure of the earth can be divided into
four main layers:
Inner core
Outer core
Mantel
Crust
The Core
At the centre of the earth is the core, which is split into
an inner core and an outer core.
It is the densest part of the planet, being made of rocks rich in iron and nickel.
The outer core is semi-molten and contains a solid inner core with a temperature of over
6,000°.
The Mantle
Surrounding the core is the mantle, which is largely composed of silicate rocks rich in iron
and magnesium.
The part of the mantle nearest the core is quite rigid.
The layer above this, the asthenosphere, is semi-molten, with temperatures near the core
reaching 5,000°.
These high temperatures generate convection currents.
The Crust
The thinnest layer is the crust, which has the coolest, least dense rocks.
These rocks are rich in silicon, oxygen, aluminium, potassium and sodium.
There are two types of crust: oceanic and continental.
Oceanic crust is and mainly basalt in nature and around 6-10 km thick so less dense.
Continental crust is composed of a wide variety of igneous, metamorphic and sedimentary
rocks and is as much as 70 km thick and so denser than oceanic crust.
The crust is separated from the mantle by the Mohorovijic discontinuity.
Together, the crust and the rigid upper mantle are collectively known as the lithosphere.

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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 plates meet are called plate boundaries or plate margins.
Convection Currents
1. Radioactive decay of some elements in the mantle and core generate a lot of heat
2. When lower parts of the asthenosphere
heat up, they become less dense and
slowly rise
3.…read more

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In the 17th century people first noticed that South America and Africa looked like they could
fit together. There were suggestions that the continents might once have been joined
together before moving apart, but most people believed the continents were fixed in place.
In 1912 Alfred Wegner proposed the theory of continental drift. He suggested that all the
continents were once joined as one supercontinent called Pangea which drifted apart.…read more

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Continental Fit
Some continents, such as the western seaboard or Africa and the
eastern seaboard of South America, seem to fit together if placed
beside each other. This is particularly true if the continental shelves
are taken into account as the true edges of the land masses.
Geological Evidence
Areas of South America and Africa have rocks of the same age and composition ­ if you fit these
continents together, the distribution of rock matches up.…read more

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Palaeomagnetism
In 1948 a survey of the floor of the Atlantic Ocean revealed a continuous ridge running
largely north to south. It proved to be around 1,000 km wide, reaching heights of 2.5 km,
and was composed of volcanic rocks.
This suggested sea-floor spreading was occurring. The evidence for this is the alternating
polarity of the rocks that form the ocean crust.
As magma erupts from mid-ocean ridges, magnetic minerals in the molten rock align
themselves with the direction of the Earth's magnetic field.…read more

Comments

Naeemah

Hi, i find these resources excellent. I was wondering if you have anymore on this topic about earthquakes and tsunamis. Additionally, do you also have notes on weather and climate? and Globalisation and Development?

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