Earth's crust

The earth's crust 

The Earth’s crust is a thin hard outer shell of rock which is a few dozen kilometres thick. The crust is made mostly from oxygen and silicon, with aluminium, iron, calcium, magnesium, sodium, potassium, titanium and traces of 64 other elements. There are two kinds of crust oceanic and continental. 

Earth's crust

 

 

 

 

 

 

 

Oceanic Crust 

 Oceanic crust is the crust beneath the oceans. It is much thinner - just 7 km thick on average. It is also young, with none being over 200 million years old. 4 The Earth’s crust contains 92 elements. 

 Continental crust 

 Continental crust is the crust beneath the continents. It is up to 80 km thick and mostly old.Continental crust is mostly crystalline ‘basement’ rock up to 3800 million years old. Some geologists think at least half of this rock is over 2500 million years old. 

 Mantle

 Under the crust, there is a deep layer of hot soft rock called the mantle . The crust and upper mantle can be divided into three layers . The mantle makes up the bulk of the Earth’s interior. It reaches from about 10-90 km to 2890 km down. As you move through the mantle temperatures climb steadily, until they reach 3000°C. Mantle rock is so warm that it churns slowly round like very, very thick treacle boiling on a stove.
 This movement is known as mantle convection currents. Mantle rock moves about 10,000 times more slowly than the hour hand on a kitchen clock. Cooler mantle rock takes about 200 million years to sink all the way to the core. Near the surface, mantle rock may melt into floods of magma. These may gush through the upper layers like oil that is being squeezed from a sponge.
 The lithosphere,
 The asthenosphere 
 The mesosphere. 
The upper mantle is made up of iron and magnesium silicates; the lower is silicon and magnesium sulphides and oxides. .The outer core Beneath the mantle is a core of hot iron and nickel. The outer core is so hot - climbing from 4500°C to 6000°C that it is always molten. 

The inner core  of earth

The inner core is even hotter (up to 7000°C) but it stays solid because the pressure is 6000 times greater than on the surface. 

 Bulk of the earth 

The bulk of the Earth is made from iron, oxygen, magnesium and silicon. More than 80 chemical elements occur naturally in the Earth and its atmosphere. 

 The lithosphere 

The lithosphere is the upper, rigid layer of the Earth. It consists of the crust and the top of the mantle . It is about 100 km thick.The lithosphere was discovered by‘seismology’, which means listening to the pattern of vibrations from earthquake The boundary between the lithosphere and the asthenosphere occurs at the point where temperatures climb above 1300°C.
The lithosphere is only a few kilometres thick under the middle of the oceans. Here, the mantle’s temperature just below the surface is 1300°C.The lithosphere is thickest - 120 km or so - under the continents.The Earth’s crust is thin and rocky. All areas of wet and dry land are part of this crust, including the ocean floor. It is estimated that approximately one cubic kilometre of new continental crust is probably being created each year. The‘basement’ rock has two main layers: an upper half of silica-rich rocks such as granite, schist and gneiss, and a lower half of volcanic rocks such as basalt which have less silica. Ocean crust is mostly basalt. 
 Continental crust is created in the volcanic arcs above subduction zones (see converging plates). Molten rock from the subducted plate oozes to the surface over a period of a few hundred thousand years. The boundary between the crust and the mantle beneath it is called the Mohorovicic discontinuity.
 The Horn of Africa and the Red Sea is one of the places where the Earth’s thin oceanic crust is cracked and moving. It is gradually widening the Red Sea. The mantle makes up the bulk of the Earth’s interior. It reaches from about 10-90 km to 2890 km down. As you move through the mantle temperatures climb steadily, until they reach 3000°C.
 Mantle rock is so warm that it churns slowly round like very, very thick treacle boiling on a stove. This movement is known as mantle convection currents. Mantle rock moves about 10,000 times more slowly than the hour hand on a kitchen clock. Cooler mantle rock takes about 200 million years to sink all the way to the core. Near the surface, mantle rock may melt into floods of magma. These may gush through the upper layers like oil that is being squeezed from a sponge.
 The boundary between the mantle and the core (see Earth’s interior) is called the core-mantle boundary (CMB). The CMB is about 250 km thick. It is an even more dramatic change than between the ground and the air. Temperatures jump by 1500°C at the CMB. 
The difference in density between the core and the mantle at the CMB is twice as great as the difference between air and rock. Scientists have found ‘anti-continents’ on the CMB that match with continents on the surface. Every now and then, mantle rock melts into floods of magma, which collects along the edges of tectonic plates. It then rises to the surface and erupts as a volcano.