Picture
\nBefore the development of plate tectonic theory, earth scientists divided the interior of the Earth into three layers; the crust, the mantle and the core.<\/p>\n
The Core
\nMade up of dense rocks containing iron and nickel alloys and is divided into a solid inner core and a molten outer one, with a tempeature of over 5,000 degrees Celsuis.<\/p>\n
The Mantle
\nThis is made up of molten and semi-molten rock containing lighter elements such as silicon and oxygen.<\/p>\n
The Crust
\nThis is even lighter because of the elements that are present, the most abundant being silicon, oxygen, aluminium, potassium and soidium. The crust varies in thickness – beneath the oceans it is only 6-10km thick but below the continents this increases to 30-40km. Under the highest mountain ranges the crust can be up to 70km thick.<\/p>\n
The crust and upper mantle can be further subdivided into two more sections:
\nLithosphere – this consists of the crust and the rigid upper section of the mantle and is approximately 80-90 km thick. It is divided into seven very large plates and a number of smaller ones.
\nAsthenosphere – this is below the lithosphere and is semi-molten and the plates float and move on this.
\nMap of major plate boundaries
\nPicture
\nThere are two different types of crust
\nOceanic crust
\nThickness: 6-10km
\nAge: less than 200 million years ago
\nDensity: very dense
\nComposition: mainly basalt; silicon, magnesium and oxygen
\nForms constantly
\nCan be destroyed
\nContinental curst
\nThickness: 30-70km
\nAge: Over 1,500 million years
\nDensity: not very dense
\nComposition: mainly granite, silicon, aluminium, oxygen
\nIs not formed
\nUnlikely to be destroyed
\nWhy do the plates move?
\nPicture
\nHotspots around the core of the Earth generate thermal convection currents within the asthenopshere, which cause magma to rise towards the crust and then spread before cooling and sinking. This circulation of magma is the vehicle upon whch the crustal plates move. The crust can be thought of as ‘floating’ on the more dense material of the asthenosphere. this is a continuous process with new crust being formed along the line of constructive boundaries between plates (where plates move apart from each other) and older crust being destroyed at destructive boundaries (where plates are moving towards each other.<\/p>\n","protected":false},"excerpt":{"rendered":"