The atmosphere is a mixture of gases surrounding the Earth from all sides. It is an essential component of Earth because all living organisms depend upon air for survival. Humans may survive for some time without food and water, but cannot survive even a few minutes without air. The atmosphere contains important life-supporting gases such as:
Almost 99 per cent of the total mass of the atmosphere is confined within 32 km from the Earth’s surface. Air is colourless and odourless and is felt only when it moves as wind.The atmosphere also protects life on Earth through the ozone layer, which absorbs harmful ultra-violet rays from the Sun.
The atmosphere is composed of:
The proportion of gases changes with altitude.
Carbon dioxide is meteorologically very important because:
The amount of carbon dioxide has increased in recent decades mainly due to:
This increase has contributed to rising atmospheric temperature.
Ozone is found between 10 km and 50 km above Earth’s surface.
Thus, ozone protects life on Earth.
Water vapour is a variable gas in the atmosphere and decreases with altitude.
| Region | Approximate Quantity |
|---|---|
| Warm and wet tropics | Up to 4% of air volume |
| Desert and polar regions | Less than 1% |
Water vapour also decreases from:
The atmosphere contains small solid particles originating from different sources.
These particles are mainly concentrated in lower atmospheric layers.
Higher concentration is found in:
due to dry winds.Lower concentration occurs in:
Dust and salt particles act as:
around which water vapour condenses to form:
The atmosphere consists of layers having different:
Density decreases with increasing altitude.Based on temperature conditions, the atmosphere is divided into:
The troposphere is the lowermost layer of the atmosphere.
| Region | Height |
|---|---|
| Equator | About 18 km |
| Poles | About 8 km |
| Average | About 13 km |
The troposphere is thickest at the equator because strong convectional currents transport heat to great heights.
Temperature decreases at the rate of:
1∘C for every 165 m
This is the most important layer for biological activities.
The boundary separating troposphere and stratosphere is called the tropopause.
| Region | Temperature |
|---|---|
| Equator | About −80°C |
| Poles | About −45°C |
Temperature remains nearly constant in this zone.
The stratosphere lies above the tropopause and extends up to about 50 km.
The mesosphere extends up to about 80 km above the stratosphere.
The upper boundary is called the mesopause.
The ionosphere lies between about 80 km and 400 km.
The exosphere is the uppermost atmospheric layer.
The major atmospheric elements influencing human life are:
These elements constantly change and determine weather and climate conditions.
| Layer | Approximate Height | Major Characteristics |
|---|---|---|
| Troposphere | 8–18 km | Weather phenomena, water vapour, dust |
| Stratosphere | Up to 50 km | Ozone layer |
| Mesosphere | Up to 80 km | Temperature decreases sharply |
| Ionosphere | 80–400 km | Radio wave reflection |
| Exosphere | Above thermosphere | Merges with outer space |