Observation

This question was very popular among the candidates and majority of them performed very well

Internal structure of the Earth
(a) Diagram.

(b) (i) Characteristics of the Earth’s crust
- covered by the gases of the atmosphere
- outermost layer of the solid Earth
- made up of rocks and minerals
- has upper part and lower part
- upper part is made of granitic rocks
- upper part forms continents
- upper part is made up of silica and alumina hence, its name Sial
- density of Sial is 2.7
- Sial is lighter and floats on Sima
- Sima is made up of denser basaltic rocks
- lower part of the earth crust is made up of Sima
- the ocean floors are made of Sima
- density of Sima is 3.0
- Sima contains silica and magnesia
- the thickness of the crust varies from 5-6 km beneath the ocean to about 48km under the continent
- presence of living things on the crust

(ii) Characteristics of the atmosphere
- uppermost layer of the earth
- it is the gaseous layer that envelopes the Earth
- has no colour
- has no odour
- clouds of different types are formed
- contains water vapour in varied proportions
- precipitation is formed in the atmosphere
- contains aerosols
- held to Earth by the gravitational force of the Earth
- the phenomenon of weather occurs in the atmosphere
- thunder and lightning are formed in the atmosphere
- gases like nitrogen, oxygen, carbon dioxide, argon and ozone are found in the atmosphere
- ozone layer is located 30 – 50 km above Earth surface
- it extends to an altitude of 1,000 km
- atmosphere is divided into layers e.g. troposphere. stratosphere, mesosphere and thermosphere
- temperature decreases with altitude within the lower atmosphere (troposphere)
- air pressure decreases with altitude within the atmosphere