Atmosphere: Layers of the Atmosphere in Order

Going by the simplest definition possible, atmosphere is the mass of air surrounding the Earth. This mass of air, which is believed to extend over a vertical distance of about 6200 miles, is basically divided into five zones or layers. These layers, starting from the surface of the Earth, are troposphere, stratosphere, mesosphere, thermosphere and exosphere. Each of these layers of the atmosphere have distinct characteristics which differ it from the other.

Layers of the Atmosphere

The mass of all the atmospheric layers combined adds up to 1.10231131 × 10¹⁹ pounds, and approximately 80 percent of this can be attributed to the troposphere alone. Each of these layers of the atmosphere have some unique characteristic of its own - details of which are discussed below.

Troposphere: The first layer of the Earth's atmosphere, troposphere starts from the surface of the planet, and extends up to a vertical distance of 4.34 miles near the poles and 10.56 miles near the equator. The temperature of troposphere decreases with altitude, which means that the lowest part of the layer is the warmest at any given point of time. This trend of temperature can be attributed to the fact that this layer is most often heated by transfer of energy from the surface. On an average the temperature here drops at a rate of approximately 6.5°C per 1000 meters, in a phenomenon referred to as the Environmental Lapse Rate. Troposphere is separated from stratosphere by the atmospheric boundary referred to as the tropopause.

Stratosphere: The second layer of the Earth's atmosphere, stratosphere extends from tropopause to a vertical distance of 32 miles. Unlike troposphere, the temperature in stratosphere increases with altitude. This layer contains approximately 19.9 percent of the total mass of the atmosphere. The temperature in this layer remains constant with height for the first 5.59 miles, but increases with altitude for next 12.42 to 31.06 miles. The ozone layer, which is very crucial for life forms on Earth, also lies in this zone. It is separated from mesosphere by the atmospheric boundary referred to as the stratopause.

Mesosphere: The third layer of the atmosphere, mesosphere extends from stratopause to a vertical distance of around 50 - 53 miles. In mesosphere, temperature decreases with altitude. It is separated from the thermosphere by the mesopause, which is also the coldest place of the Earth, with a temperature of around -100°C (-148.0°F). Mesosphere is the layer wherein most of the meteors burn when they enter the atmosphere of the Earth.

Thermosphere: The fourth, and also the biggest of the atmosphere layers, thermosphere extends to a vertical distance of around 220 - 500 miles. In thermosphere, the temperature increases with altitude, and can reach up to 1200°C at times. The oxygen molecules in this zone contribute to this rising temperature by absorbing the intense solar radiation. Located within the thermosphere is ionosphere, a layer which contains electrically charged gas particles that help in transmission of radio signals. The highest point of thermosphere, thermopause, and the lowest point of the exosphere, exobase, combine to form an atmospheric boundary between the two layers.

Exosphere: The outermost layer of the atmosphere of the Earth, exosphere extends from thermospause into the space. This layer is mainly made up of hydrogen and helium. Though the definite boundary of this atmospheric layer is not known, scientists believe that this layer extends for a vertical distance of 6200 miles. However, this is not supported by substantial evidence, and hence thermosphere is referred to as the biggest layer amongst all these layers of Earth's atmosphere.

Each of these layers of the atmosphere play a crucial role in making planet Earth the only planet with life. Without this protective covering, the Earth would have been as 'dead' as the other planets in the universe.