Our Environment

Spheres of Earth

Do you know why life exists only on planet earth?

Our planet earth is unique in the solar system because it is the only planet on which life exists. It happens because of the following reasons:

Suitable Atmosphere: Atmosphere may be defined as the layer of gases surrounding any celestial body. Our planet earth has oxygen along with other gases such as nitrogen and hydrogen, which is required for sustaining life of most organisms.

It is the composition of air that helps in sustaining life on earth.

Let us study how.

1. Presence of ample amount of oxygen: Oxygen is required for the survival of most of the living organisms (all eukaryotes and some prokaryotes). It is constantly added into the atmosphere by green plants and trees.

2. Presence of less amount of carbon dioxide: On earth, carbon dioxide is used by green plants and some other photosynthesizing organisms. It is also utilised by some marine animals to manufacture their shells. The percentage of CO₂ is very less on earth. It makes up only 0.03% of the earth’s atmosphere. However, it is found in 95% - 97% of the atmosphere on planets such as Venus and Mars.

Do you know why the atmosphere of earth is held in place?

The atmosphere of earth is held in place due to the pull of gravity. The atmosphere of the earth contains 78% nitrogen, about 21% oxygen, 0.03% CO₂, and other gases.

3. Size of earth: The size of a planet decides the amount of gravity it possesses. The earth is large enough to be able to hold its atmosphere. Some other planets such as Mars and Mercury are too small to hold their atmosphere. Therefore, these planets have very thin atmospheres.

• Suitable temperature:

A suitable temperature on earth is governed by suitable atmosphere.

Can you tell how?

Carbon dioxide traps the infrared radiations of the sunlight and thus helps in keeping the atmosphere warm. Our planet earth has right amount of carbon dioxide that keeps the atmosphere neither too hot nor too cold.

• Presence of Water: Water is the essence of life. It is necessary for the survival of living organisms. It contains oxygen and not harmful elements such as those present in other liquids.

Water on earth is found in three states − solid, liquid, and gas.

Hydrosphere may be defined as the aqueous part of earth or its atmosphere. It includes all the water bodies and water vapours.

• Proper amount of sunlight: The earth is in perfect position in the solar system so that it receives the right amount of heat from the sun. The light received is enough for plants to photosynthesise and living organisms to survive.

Parts of Earth

The earth consists of following parts (spheres):

1. Lithosphere
2. Hydrosphere
3. Atmosphere

All the living organisms including plants, animals, and unicellular organisms constitute biosphere.

In addition to these life sustaining factors, the earth also has a strong mechanical outer layer that can tolerate stress. This outer layer of earth which is approximately 100 km thick is known as lithosphere. It consists of crust and mantle. Thus, it can be concluded that the earth’s system has four major sub-systems − land, water, air, and living things. Each of these four sub-systems is called spheres.

Now that we know why life exists only on earth, let us study the basic requirements of all life forms on earth. All these sub-systems are interdependent and interrelated. For example, the living organisms (biosphere) require all the other spheres (lithosphere, atmosphere, and hydrosphere) for survival. Thus, air, land, water, and minerals are known as natural resources.

 

Levels of Organisation

Now you know that biosphere consists of all the living organisms on Earth. These organisms interact with each other and the non living components of their environment. The biosphere is di…