SSC Exam » SSC Study Materials » Physical Geography » The Earth: Shape and Size

The Earth: Shape and Size

The atmosphere of the Earth is composed of several layers of gases. The Earth is surrounded by the gas layers and remains constant by the gravity of Earth.

There are five atmospheric layers surrounding the Earth, including troposphere, stratosphere, mesosphere, thermosphere and exosphere. The main composition of the atmosphere is the gaseous molecules. The density of the main atmospheric composition is relatively higher in the troposphere than in other atmospheric layers. The main gaseous substances in these layers include nitrogen, oxygen, carbon dioxide and other gases. The density of the gas molecules is higher in the lowest layer from land. Due to the presence of the gaseous substance, all the weather events occurred in this layer. The density of gas decreases gradually with an increase in height. The gaseous composition of the atmosphere is an important component of nature for the survival of living beings. 

Composition of   Atmosphere

The atmosphere of the Earth is commonly known as air. The atmosphere is generally composed of different gas layers, which are retained strongly by the Earth through Earth’s gravitational force. The pressure of atmospheric compositions allows the water to exist on the surface of the Earth. The gas competitions of the atmosphere are very beneficial for the living hood of entire living beings on the Earth. The composition of the atmosphere, mainly the gaseous components, has a major impact on biodiversity. The gaseous components of the atmosphere are also known as environmental components. There are many gas components in the atmosphere. The atmosphere has a mass due to the presence of gaseous components. The mass of the whole atmosphere is 5.15×1018 kg. Three-quarters of the total mass of the atmosphere is present within 11 kilometres from the Earth’s surface. The mass of the atmosphere decreased gradually with altitude. Moreover, the density of air is thinner in high altitudes. 

The percentage of different gas compositions is different, and those are beneficial for different purposes of living organisms. The main gas composition of the atmosphere includes Nitrogen, oxygen and carbon dioxide. In addition, there is a minute percentage of water vapour present in the atmosphere. Another important gas composition of the atmosphere is the ozone gas, the gaseous molecule of ozone that forms an ozone layer on the upper surface of the stratosphere. The ozone layer protects the Earth’s surface from entering the ultraviolet rays from the sun. The ozone gas molecule in ozone layers absorbs the ultraviolet rays of sun rays and saves the Earth from overheating. The pressure of the gaseous composition decreased gradually with high due to the lower density of the gas components in the higher surface of the atmosphere. The atmospheric changes due to the change in the gaseous composition may cause many environmental issues like changes in weather, volcanisms etc. 

Description of atmospheric composition

The atmospheric composition is mainly made up of gases. The gaseous components of the atmosphere are responsible for the composition of air. The air is built up of a mixture of different gas molecules. The major gas molecules in the air or atmosphere are Nitrogen, oxygen and carbon dioxide. The different gas molecules are present in the atmosphere in different percentages. The gas components have different specific importance for living beings and nature. The different composition of the atmosphere has been described below.


Nitrogen is one of the main compositions of the atmosphere or in the air. Nitrogen is the present highest amount in the atmosphere. The percentage of Nitrogen in the air is approximately 78% among the other gaseous components in the air. This atmospheric Nitrogen is the main source to build up proteins. The nitrogen molecules are an important component for forming proteins in the living body. The nitrogen molecules are combined with oxygen molecules of air and form nitrate compounds which dissolve in rainwater during rains and are mixed with soil. The plants can absorb dissolved Nitrogen from the soil, produce protein, and reserve the protein molecules in fruits and vegetables. The animals get protein from plants. 


Oxygen is the most important atmospheric composition for the survival of living beings. Oxygen is present by 21% in the air. Moreover, all animals and plants take oxygen for respiration. Therefore, oxygen is an important component for energy generation in the living body and survival. In addition, oxygen is important for combustion; without oxygen, inflammation is impossible as oxygen helps other objects for combustion. 

Carbon dioxide

Carbon dioxide is present in the atmosphere by 0.4 %. Plants produce carbon dioxide during photosynthesis. Carbon dioxide is a toxic gas component. The amount of carbon dioxide in the air increases gradually due to air pollution, which causes global warming. 


The atmosphere is the surrounding gas layer of the Earth. The layers of the atmosphere remain attached by the Earth’s gravitational force. The mass of the atmosphere exerts pressure on the surface of the Earth. The atmospheric pressure makes it possible for water on Earth’s surface. The composition of the atmosphere is mainly the gaseous components. The main gas components are, Nitrogen, oxygen and carbon dioxide. Water vapour and inert gases, mainly argon are present in minute percentages in the air. The density of the atmospheric composition decreases with altitude. 


Frequently asked questions

Get answers to the most common queries related to the SSC Exam Preparation.

What are the key features of physical geography?

Ans :  The key features of physical geography is the natural environment that consists of l...Read full

What are the components of physical geography?

Ans : The four components of physical geography are atmosphere, biosphere, hydrosphere and lithosph...Read full

What causes the movement of wind?

Ans : Wind is the movement that is caused by air through the uneven heating of the earth formed by ...Read full

How many types of wind are there?

Ans : There are three types of wind which are primary wind, secondary wind, and tertiary wind.