Structure of the Earth

Earth’s Interior Greatest depth reached by humans - 8km Knowledge derived from the study of seismic waves.

Seismic Waves P Waves – Primary Waves. They are longitudinal waves like sound waves in which movement of particles is in the direction of propagation of waves. It can travel through all mediums i.e solid, liquid and gases.

Seismic Waves S Waves – Secondary Waves. Transverse like light waves. Movement of particles is at right angle to the direction of waves. They can travel through solids only and disappear in liquids.

Seismic Waves L Waves – long waves, also called surface waves. Travels along the surface of the earth. Moves particles in a circular path. Of two types – Rayleigh waves and Love waves.

Earths Interior

Lithosphere Derived from the Latin word ‘Lithos’ meaning rocks. Outermost layer also called the mineral skin. This is the outermost solid crustal layer.

Lithosphere Main rocks – granite and basalt. Temp. increases at the rate of 1⁰C for every 32m depth. Divided into 2 layers – Sial and Sima.

Sial Continental Crust Discontinuous layer formed of granitic rocks Silicate and aluminium Lighter – 2.7gm/cu.cm density. 25km thickness

Sima Oceanic Crust Continuous layer formed of basaltic rocks Silicate and Magnesium Heavier – density 3.0gm/cu.cm 35km thickness

Mohorovic Discontinuity Boundary between the Lithosphere and the Mantle.

Mantle Thick Fluid Layer below the crust Consists of silicates and metals and is rich in Olivine. Density between 3.0 to 5.5 gm/cu.cm Thickness 2,840km

Aesthenosphere Upper mantle - in a partially molten state. The transition zone separates the upper mantle from the lower mantle.

Lower Mantle Lower Mantle - high pressure of overlying layers keep this in a solid state. Temp. reaches upto 2208⁰C.

Gutenburg Discontinuity It forms the boundary between the mantle and the core.

Barysphere Also called the core Nife - Nickel and Iron Liquid iron generates its own electricity - the source of the earth’s magnetic field.

Core Heaviest layer – density 13 to 15 gm/cu.cm Temp. of about 5000⁰C Radius of about 3500km Outer Core - behaves like liquid Inner Core - behaves like solid

Shadow Zone Region on the globe opposite to the earthquake focus where S waves are not received as it is unable to pass through the core.