STRUCTURE OF EARTH’S INTERIOR

Sources providing knowledge about interior of earth

1. Artificial Sources2. Evidences from the theories of the origin of

earth 3. Natural Sources

P waves

S wave

L waves

Wave pattern

Interior of Earth

CRUST• This is the relatively thin layer of rock which envelopes the

interior of the earth • The average thickness of the crust is about 60km• The thickness of the crust is greater below the continents

than under the ocean floor • Solid rocks form the crust and the density of the rocks

increases with the depth • Silicon, Aluminium and Magnesium are the chief elements

that make up this layer • The average density of the outer and lower crust is 2.8 and

3.0 respectively • The boundary between crust and mantle is called Mohorovic

Discontinuity or Moho

MANTLE

• The Mantle having mean density of 4.6• It extends for a depth of 2900km inside the earth • It contains 83 percent of the total volume and 68

percent of total mass of earth • The velocity of the seismic waves relatively slows down

in the upper most zone of the mantle for a depth of 100 to 200 km. This zone is called the zone of low velocity

• Mantle contains silicate minerals rich in iron and magnesium

CORE• Core is the deepest and the most inaccessible zone of the

earth • It extends from the lower boundary of the mantle at the

depth of 2900km to the centre of the earth • The mantle – core boundary is known as Weichert –

Gutenberg Discontinuity • There is a sudden increase of density from 5.5 to 10.5,

indicated by the sudden increase in the velocity of P waves • S waves disappear in outer core which means that outer

core should be in molten stage