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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…

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