Many candidates attempted this question. However, some of them took the external structure of the earth to mean the internal structure of the earth. The diagram of the external structure of the earth should include the atmosphere, lithosphere, hydrosphere and biosphere. The characteristics of each ofthe layers include:
Atmosphere
the layer of gases enveloping the earth;
the gases include oxygen, nitrogen, carbon - dioxide, helium etc;
living things depend on gases for survival;
the atmosphere consist oflayers e.g. troposphere, stratosphere, ionosphere and exosphere;
density decreases with attitude;
one of its constituents is water vapour.
Lithosphere
this is the solid portion of the earth;
it is the outermost layer of the earth crust;
it consist of two parts, sial and sima;
it forms the continents;
its average density is 2.7.
Hydrosphere
it is the liquid part of the earth;
it consists of water bodies such as oceans, seas, rivers, lakes etc;
it covers 70% of the earth's surface;
it is the habitat of aquatic organisms.
Biosphere
zone of living organisms;
contains air, water and minerals;
found in the lithosphere, atmosphere and hydrosphere;
it links all other zones of the earth together.
Many of the candidates who answered the question were able to give the importance of the atmosphere. Many candidates attempted this question. However, some of them took the external structure of the earth to mean the internal structure of the earth. The diagram of the external structure of the earth should include the atmosphere, lithosphere, hydrosphere and biosphere. The characteristics of each ofthe layers include:
Atmosphere
the layer of gases enveloping the earth;
the gases include oxygen, nitrogen, carbon - dioxide, helium etc;
living things depend on gases for survival;
the atmosphere consist oflayers e.g. troposphere, stratosphere, ionosphere and exosphere;
density decreases with attitude;
one of its constituents is water vapour.
Lithosphere
this is the solid portion of the earth;
it is the outermost layer of the earth crust;
it consist of two parts, sial and sima;
it forms the continents;
its average density is 2.7.
Hydrosphere
it is the liquid part of the earth;
it consists of water bodies such as oceans, seas, rivers, lakes etc;
it covers 70% of the earth's surface;
it is the habitat of aquatic organisms.
Biosphere
zone of living organisms;
contains air, water and minerals;
found in the lithosphere, atmosphere and hydrosphere;
it links all other zones of the earth together.
Many of the candidates who answered the question were able to give the importance of the atmosphere.