Chapter 8 - Interior of earth

The configuration of the surface of the earth is largely a product of the processes operating in the interior of the earth. Exogenic as well as endogenic processes are constantly shaping the landscape.

The Crust (SIAL - Silica & Aluminium)

• It is the outermost solid part of the earth. 
• It is brittle in nature. 
• Oceanic crust is thinner as compared to the continental crust. The mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km. The continental is as much as 70 km thick in the Himalayan region.
• It is made up of heavier rocks having density of 3 g/cm3. This type of rock found in the oceanic crust is basalt. 
• The mean density of material in oceanic crust is 2.7 g/cm3.

The Mantle (SIMA - Silica & Magnesium)

• The portion of the interior beyond the crust is called the mantle.
• The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
• The upper portion of the mantle is called asthenosphere. It is considered to be extending upto 400 km. It is the main source of magma
• It has a density higher than the crust’s (3.4 g/cm3).
• The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km.
• The lower mantle extends beyond the asthenosphere. It is in solid state.

The Core (NIFE - Nickel & Iron)

• The outer core is liquid in state while the inner core is in solid state
• The density at the mantle core boundary is 5 g/cm3 while at the centre of the Earth at 6300 km it is 13 g/cm3
• The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the nife layer.

- Earth's mass is mostly composed of - Iron (32.1 %)

- The most abundent element Earth's Crust - Oxygen (46.5 %)

 Rocks

Petrology - Science of Rocks

Pedology - Soil Science

Igneous Rock

• Solidified from Magma & Lava
• Consist 40-80 % Silica
• All other rocks originates from these rocks so it is also called Primary Rock
• Examples - Granite, Basalt, Gabbro, Pegmatite, etc

Sedimentary Rock

• Depositions of fragments of rocks by exogenous process & fossil called 'Lithification'
• Holds all reserves of coal, oil & natural gas
• Example - Sandstone, Coglomerate, Limestone, Shale, Loess

Metamorphic Rocks

• Formed under PVT (Pressure, Volume & Temperature)
• Examples - Granite, Marbel, Quartzite, Slate, Gneiss, Schist

Indian Deccan Plateau consists of Basalt rocks

Earthquakes

• Sudden shaking of Earth due to release of Earth's energy from its Crust
• Focus or Hypocentre - Point where energy releases
• Epicentre - Point on the surface, near to Focus
• Lithosphere- Place of all natural earthquake (200 Km Depth)
• "Sismograph" - Instrument that record waves
• "Richter Scale" - Instrument that measures Earthquake

Earthquake Waves

They are of two types :-

i. Body Wave - are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. They are also of two types 

1. Primary Wave or P wave (Longitudnal)

• Faster & Ist one to arrive surface
• Travels through out Solid, Liquid & Gas
• Travels with the speed of sound

     2.  Secondary Wave or S wave (Transeverse)

• Travels only in Solids
• Travels half the speed of Sound

ii. Surface Wave - move along the surface. The velocity of waves changes as they travel through materials with different densities. The denser the material, the higher is the velocity.

• Last to report on the graph
• More Distructive
• Velocity is slower than P & S but Duration & Amptitude is very high

- "Shadow Zone" - are place where waves are not reported

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