The word Atmosphere is taken from the modern Latin word ‘atmosphaera’. Which meaning is gaseous envelop surrounding the earth and from the Greek word “Atmos” meaning ‘Vapour steam. {atmo + spheria (sphere) make atmosphere.}
Life is impossible without air because it is the basic source of our breathing. we live on lithosphere and it is completely of air as like a balloon. The air consists of various gases i.e., Nitrogen, Oxygen, argon, carbon dioxide, neon, helium, etc. All the organisms are need oxygen for breathing while plants need carbon dioxide for making their food. Ozone is also an important gas in the atmosphere, it protects us from harmful ultraviolet rays. All these gases along with water vapours and dust particles together form our atmosphere.
The atmosphere can be defined as the layer of gases that surround our planet. It provides us with air to breathe and protects us from the harmful effects of the sun’s rays.
Importance of the Atmosphere
Oxygen is essential for breathing. It is also known as life gas because it is the basis for life for all organisms. It is also required for combustion. Nitrogen helps in the growth of living organisms. It controls fire. Carbon dioxide absorbs heat radiated by the earth. As a result, it keeps the earth warm. It is also essential for the growth of plants. Ozone protects us from the harmful effects of the sun’s rays. Along with these gases, dust particles and water vapours are also present in the atmosphere.
The concentration of gases, water vapours and dust particles varies from place to place and from time to time. Water vapours mainly found near the oceanic areas. Land areas have relatively less concentration of water vapours. Hygroscopic nuclei is dust particles because they provide a centre around which the rain droplets form and bring rainfall to the surface. The gases, dust particles and water vapours are mainly in the lower layers of the atmosphere.
Different Layers (Structure) of the Atmosphere
The atmosphere extends up to a height of 1,600 km. from the earth’s surface. Our atmosphere is present in different layers because the concentration of various gases varies with height from the earth’s surface. The heavier gases like carbon dioxide, nitrogen, oxygen, etc are near the earth’s surface. While lighter gases are at higher altitudes. As we go higher, the atmosphere becomes thinner. The atmosphere divided into five layers based on composition, temperature and other properties. These are the troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.)
1. Troposphere:
It is the lowest layer of the atmosphere starting from of the earth’s surface. All the weather phenomena are found in this layer. We are in direct contact with this layer. Oxygen, carbon dioxide and nitrogen are its main gases. The troposphere extends up to 20 km from the surface.
2. Stratosphere:
Stratosphere is the second layer of the atmosphere. It extends up to a height of about 50 km. It is a layer of calmness because it is free from all weather phenomena. Due to this quality, the stratosphere is examine an ideal layer for jet planes. Ozone is present in this layer. Temperature increases in this layer because upwards. The atmosphere exerts pressure on the ozone to absorb harmful ultraviolet rays.
3. Mesosphere:
It is the third layer of the atmosphere and lies above the stratosphere. It extends up to a height “of about 80 km. In this layer, temperature decreases with height.
4. Thermosphere:
Thermosphere is the fourth layer of the atmosphere. It is also called the Ionosphere. It extends up to a height of about 400 km this layer reflects the radio waves to the earth’s surface. Hence, this layer is important for communication.
5. Exosphere:
It is the uppermost layer of the atmosphere. It extends up to a height of 750 km from the earth’s surface. This layer merges gradually with the interplanetary space.
Density of the Atmosphere
The density of the atmosphere refers to the water vapour present in the air. As you know the atmosphere is a mixture of gases. Due to the gravitational force, it is hold on to the earth’s surface.
The density of the atmosphere varies from place to place. It is the densest near the surface. As the altitude increases, density decreases.
i.The dense air is heavier than the thin air. Thus, it exerts more pressure on the earth’s surface.
ii. The dense air is generally near the surface, mainly at the ocean surface. We find more atmospheric pressure in seas than in the hills or mountains. The density of the atmosphere decreases rapidly as we go up. That is why, mountaineers experience problems breathing at high altitudes. They keep oxygen cylinders with them while climbing the mountains.
Movement of Air
The temperature also decreases as we go upwards. The atmosphere exerts pressure on the earth which varies from place to place. Some areas have high pressure of air while others experience low pressure. Air moves from high-pressure areas to low-pressure areas. Such movement of air is known as wind.
Composition of the Atmosphere
Nitrogen, oxygen, argon, carbon dioxide, neon, helium, ozone, hydrogen, etc. are the main gases present in the atmosphere.
The following table shows the major gases along with their percentage by volume in the atmosphere
Major Gases and Percentage of Volume
| S.no | Gases | Percentage of Volume |
|---|---|---|
| 1 | Nitrogen | 78.08 |
| 2 | Oxygen | 20.94 |
| 3 | Argon | 0.93 |
| 4 | Carbon dioxide | 0.03 |
| 5 | Neon | 0.0018 |
| 6 | Helium | 0.0005 |
| 7 | Ozone | 0.00006 |
| 8 | Hydrogen | 0.00005 |
The atmosphere is the gas and aerosol envelope that extends from the ocean, land and ice-covered surface of a planet outward into space. The density of the atmosphere decreases outward because of the gravitational attraction of the planet which pulls the gases and aerosols (microscopic suspended particles of dust, soot, smoke) inward, is greatest close to the surface. Atmospheres of some planetary bodies, such as mercury, are almost non-existent. The atmosphere has escaped the relatively low gravitational attraction of the planet and has been released into space. Other planets such as Venus, Earth, and Mars. And the giant outer planets of the solar system, have retained an atmosphere. Also, Earth’s atmosphere has been able to contain water in each of its three phases (solid, liquid, gas), which has been essential for the development of life on the planet.
Earth’s Atmosphere Evolution
The current evolution of Earth atmosphere is not completely understand. It is assume that the current atmosphere resulted from a gradual release of gases both from the planet’s interior and from the metabolic activities of life forms as opposed to the primordial atmosphere which developed by outgassing (Venting) during the original formation of the planet. Current volcanic gaseous emission includes water vapour (H2o) carbon dioxide (Co2) Sulphur dioxide (So2) hydrogen sulphide (H2s) Carbon monoxide (Co), Chlorine (Cl), fluorine (F) and diatomic nitrogen (N2; consisting of two atoms in a single molecule), as well as traces of-of other substances. Approximately 85% of volcanic emissions are in the form of water vapour. In contrast, carbon – dioxide is about 10% of the effluent.
During the early evolution of the atmosphere on Earth, water must have been able to exist as a liquid. Since the oceans have been present at least three billion years given that solar output four billion years ago was only about 60% of what it is today, enhanced levels of carbon dioxide and perhaps ammonia (NH3) must have been present to retard the loss of infrared radiation into space. The initial life- forms that evolved in this environment must have been anaerobic surviving in the absence of oxygen. Also, they must have been able to resist the biologically destructive ultraviolet radiation in sunlight, which was not absorbed by a layer of ozone as it is now.
Once organisms developed the capability of photosynthesis afterthat oxygen producing in large quantities. The build-up of oxygen in the atmosphere also permitted the development of the ozone layer as O2 molecules were dissociated into monatomic Oxygen (O; consisting of single oxygen atoms ) and recombined with other O2 molecules to form triatomic ozone molecules (O3). The capability for photosynthesis arose in primitive forms of the planet between two and three billion years ago. Previous to the evolution of photosynthetic, decomposition of water vapour is major cause of producing of oxygen with the help of ultraviolet radiation.