The Structure of the Earth- the Outer Zone

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Welcome to class! 

In today’s class, we will be talking about the structure of the earth- the outer zone. Enjoy the class!

The Structure of the Earth

The outer zone

The structure of the earth is grouped into two zones:

1. The outer structure and
2. The internal structure.

Earth is unique among the known planets: it has an abundance of water. Other worlds — including a few moons — have atmospheres, ice, and even oceans, but only Earth has the right combination to sustain life.

Earth’s oceans cover about 70 percent of the planet’s surface with an average depth of 2.5 miles (4 kilometres). Freshwater exists in liquid form in lakes and rivers and as water vapour in the atmosphere, which causes much of Earth’s weather.

The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The earth’s structure is divided into two groups, namely Outer structure and Inner structure. 

The outer structure of the earth

The outer structure of the earth is made up of four zones or layers:

1. Lithosphere
2. Hydrosphere
3. Atmosphere
4. Biosphere

• Lithosphere:

This is the solid portion of the earth. It is the outermost zone of the earth which is made up of rocks and mineral materials. It represents 30% of the earth surface.

Importance

1. It forms the basis for all human settlement.
2. All mineral resources are derived here.
3. It aids transportation through the construction of roads, railways, airports, etc.
4. It aids farming activities.
5. Most human activities like mining, trading, etc are done here.

• Hydrosphere:

This refers to the liquid portion of the earth. It includes the oceans, sea, rivers, streams and springs, lakes, etc. It covers 70% of the earth’s crust.

Importance

1. Provides water for domestic uses.
2. Provides medium for transportation.
3. Provides water for industrial uses.
4. Provision of food(fishes, prawns, etc)
5. Provision of employment.
6. Serves as a tourist centre.
7. Generation of hydro-electric power(HEP)

Evaluation

1. The layer of the earth covered with water is called …….
2. Mention any four importance of hydrosphere to man.

• Atmosphere:

This is the gaseous portion of the earth. It contains 78% nitrogen, 21% oxygen, 0.03% carbon dioxide and 0.097% rare gases.

Importance

1. It is the habitat of some living organisms.
2. It provides oxygen for respiration.
3. It provides carbon dioxide for photosynthesis.
4. It provides oxygen for combustion.
5. It provides a medium of transportation.
6. It provides nitrogen for protein synthesis in plants.

• Biosphere:

This is the zone of the earth where living things are found.

Importance

1. Plants provide food for man.
2. Provision of employment.
3. Provision of raw materials.
4. Balancing and purification of the atmosphere.

Evaluation

1. State the four zones of the outer structure of the earth.
2. State three importance of atmosphere to man.

General evaluation

1. Describe the structure of the earth.
2. Explain the importance of biosphere to man.
3. State four importance of hydrosphere.
4. Mention three importance of atmosphere.
5. List three gases that can be found in the atmosphere.

Reading assignment

Essential Geography, O.A. Iwena, Pages 21-24.

Theory

1. Draw the inner structure of the earth.
2. State two importance of hydrosphere and atmosphere.

 

In our next class, we will be talking about the Structure of the Earth- the Interior Zone.  We hope you enjoyed the class.

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