Layers of the Earth's Atmosphere

Atmosphere is composed of a layer of gases that surround the planet Earth. It is composed of 78.08% nitrogen, 29.95% oxygen, 0.38% carbon dioxide and 0.93% argon. The atmosphere also contains very small amounts of other gases as also about 1% of water vapor. Atmosphere is thicker at the innermost radius around Earth and it goes becoming thinner towards the outer space. The Earth's atmosphere is composed of layers, each of which is characterized by a particular kind of constituents. The proportion of the various gases and their temperatures vary across the different layers.

The Earth's atmosphere is divided into five layers, namely, the troposphere, the stratosphere, the mesosphere, thermosphere and the ionosphere. Troposphere is the very first layer above the surface of the Earth and contains around half of the Earth's atmosphere. Stratosphere, the stable layer comes next and is followed by the mesosphere housing meteors and rock fragments. The fourth layer is the thermosphere, above which lies the last layer of the atmosphere known as ionosphere. It is a very thin layer that abounds the outer space through the exosphere. Let us look at each of the atmosphere layers in detail.

Troposphere: It begins from the Earth's surface and extends to between 7 km at the poles and 17 km at the equator. The heating caused by the solar energy reduces the density of air causing the air to rise. In the process of opposing the surrounding air, the air in this layer expends energy, resulting in a decrease in its temperature. The decreasing temperature causes the vapor content of the air to condense, resulting in an increase in the air mass. The concept of weather occurs in this layer and the air we breathe is from this very layer. Thus this layer contains about 80% of the total mass of the atmosphere.

Stratosphere: The Latin word, 'stratus' meaning 'spreading out' has given birth to the word, 'stratosphere'. It extends up to around 50 km. It is this layer of atmosphere that contains the ozone layer. The ozone layer is located between 15 to 35 km above the surface of the Earth. The ozone layer contains high amounts of ozone gas. This layer absorbs the ultraviolet radiation of the sun, which would have otherwise proved harmful to the life on Earth. Also, most of the jet aircraft fly through the stratosphere.

Mesosphere: It stretches from 50 km to around 80 to 85 km. The temperature of the air contained in this layer of Earth decreases with an increase in the height. Most of the meteors and rock fragments burn up in this layer before they can enter the Earth's atmosphere.

Thermosphere: Extending from about 85 km to more than 640 km, the temperature of air in this layer increases with height. It is relatively thin and this is where space shuttles orbit. A small change in energy can cause a large change in the air temperature of this layer. The temperature in this layer can rise up to 1,500 degrees Celsius or higher.

Ionosphere: That part of the atmosphere, which is ionized by the solar radiation, is known as the ionosphere. As some scientists call ionosphere an extension of thermosphere, ionosphere may not be regarded as a separate atmospheric layer. The ionosphere constitutes about 0.1% of the atmospheric mass. It forms the inner layer of the magnetosphere, or simply, the sphere of influence of Earth's magnetic/gravitational force. It contributes to the propagation of radio signals to distant places on Earth. It reflects radio waves back to the Earth, thus facilitating radio communication.

Exosphere: It is where the Earth's atmosphere meets the outer space. It houses free-moving particles that may migrate from the magnetosphere. It ranges from about 500-1000 km up to 10,000 km. Exosphere is the upper limit of the atmosphere. This layer is where atoms and molecules escape into space. The atmosphere becomes very thin in this layer.

The Earth is surrounded by the atmosphere that is composed of various layers. Each layer has a marked significance owing to its constituents. It is the Earth's atmosphere that is home for the very important envelope of the ozone layer. It is the atmosphere that enables communication across and beyond this world. Atmosphere is a protective covering that Earth is gifted with. It is a shield that safeguards our planet Earth and us, the earthlings.