Grade 7- The Internal Structure of the Earth

A. Crust/ Lithosphere

• Outermost layer of the earth

• Made of soils and other loose deposits of sand

• The dominant rocks are granites.

• Extends 0-50km

• Has 2 layers

1. Sial

• Also called continental crust

• Made of light coloured rocks

• Called sial because it’s made up of silica and aluminum.

2. Sima

• Also called oceanic crust

• Mainly made of basaltic rocks which are brittle.

• Called sima because it is made of silica magnesium and iron.

B. Mohorovicic Discontinuity (Moho)

• A definite zone of discontinuity between the crust and the mantle.

• Was discovered by Dr. Andrija Mohorovicic in 1909.

The Mantle/ Asthenosphere

• Layer lying between the crust and the core

• Made of iron and magnesium

• Has two layers

• Upper mantle

• Rocks are more elastic than those of sima.

• Temperature is about 1000◦c.

• lower mantle

• Rocks are like very viscous liquid.

• Temperature ranges between 1000◦c to 3000◦c.

Gutenberg Discontinuity

A definite zone of discontinuity between mantle and core.

Core/ Barysphere/ Centrosphere

• The innermost/central layer of the earth.

• Has 2 layers

• Outer Core

• Composed of very dense rocks

• Made up of nickel and iron

• Temperatures are up to 3700◦c.

• Inner Core

• A solid mass of mainly iron

• Temperatures are estimated to be 4500◦c to 5000◦c.

The Atmosphere

1. Layer of gases surrounding the earth.

2. The earth revolves with it because its held onto it by gravity

3. It’s about 330km thick.

Composition of the Atmosphere

1. Gases-exist as a mixture

2. Smoke particles

3. Dust particles

4. Water vapour.

G. Hydrosphere

Ocean and seas