The life on the Earth exists because of the atmosphere that surrounds it. It is a body of air that contains oxygen without which life on the Earth is not possible. Gases like nitrogen (78%), oxygen (just under 21%) are the main constituents of the air. Rare gases like helium, neon, argon, krypton, radon, xenon and carbon dioxide make the rest of it. The atmosphere is dense near the surface of the Earth and protects life on the planet Earth. There are five layers of the Earth's atmosphere.
The troposphere is where we breath in and is also referred to as the lower atmosphere. Of all the atmospheric layers, this is the most closest to the Earth. This layer is the birthplace of the weather, storms and rain. From the surface of the Earth, it extends out to about 3.7-5 miles (6-8 kilometers), at the poles and 10.5 miles (17 kilometers) at the equator. Most important part of the troposphere is the biosphere which extends from the surface to the maximum altitude that birds can attain.
As you move away from the surface of the Earth, the air becomes thin and temperature of the troposphere decreases by 43.7º F (6.5º C) per kilometer. However, the temperature stabilizes at 7.5 miles (12 kilometer) above the surface of the Earth. This area is called the tropopause which is considered as the boundary of the troposphere which contains about 80 percent mass of the Earth's atmosphere.
The stratosphere is above the troposphere. The Stratosphere starts from the tropopause and extends to an altitude of about 31 miles (50 kilometers) above the Earth. We can safely say that we know, all such atmospheric layers are separated by regions like the tropopause. The temperature of the lower stratosphere is about -58º F (-50º C). However, its upper level is comparatively warmer, at -0.399999º F (-18º C), even though it is below freezing point.
One of the interesting facts about this atmosphere layer is that the air is not steady and moves at a tremendous speed of 199 miles (320 kilometer) per hour. This movement of air is termed as the 'Jet Streams', which plays an important role in the weather of the Earth.
The stratosphere is very important for the preservation of animal life on the Earth. It contains Ozone in abundant quantity at its lower level i.e., 9.3 to 22 miles (15 to 35 kilometers). Ozone layer absorbs the skin cancer causing, ultraviolet radiations and thus, protects the life on the Earth. Ozone reacts with the ultraviolet rays and gives out heat, which warms the upper layers of the stratosphere. The stratopause which lies between 31 to 34 miles (50 to 55 kilometers) above the surface of the Earth, separates the stratosphere and the mesosphere.
The mesosphere lies beyond the stratosphere. It extends from the stratopause to about 49.7 miles (80 kilometers) above the Earth. In this layer, the air is very thin. Temperatures in the mesosphere can be as low as -148º F (-100º C). The mesopause has 2 minima. Recent studies have marked the weaker minimum at the 52.8 miles (85 kilometers) and the other which is considered as the stronger minimum at 62 miles (100 kilometers). It separates the layers, mesosphere and the thermosphere. These layers, together are referred to as the middle atmosphere of the Earth.
The next layer is the thermosphere, which is also referred to as the upper atmosphere. This layer extends from, the mesopause, i.e., 52.8 miles and 62 miles (85 to 100 kilometers) above the surface of the Earth to the space. The temperature in the thermosphere increases and it can be higher than 2732º F (1,500º C).
The air in the thermosphere would feel cold because the molecules of nitrogen and oxygen which absorb the Sun's energy are so far apart that the heat concentration is ineffective. This layer is divided in two sub-layers, the ionosphere and the exosphere.
Ionosphere: The ionosphere contains electrically charged molecules of the oxygen, nitrogen and other elements which reflects the radio waves back to the Earth and enables the long distance communication. The ionosphere stretches from 49.7 miles to 341 miles (80 to 550 kilometers), above the Earths surface. An increased solar activity which is apparent from the increase in the number of solar spots, can disturb the radio communication as it increase the number of charged particles in the ionosphere.
From ionosphere (621 miles or 1,000 kilometers), the exosphere stretches into the space. The thermosphere and exosphere meet at thermopause which is also called the exobase. Thermopause lies between 155 to 310 miles (250 to 500 kilometers) above the earth surface. It is calculated that exosphere sides (lower limit) with the thermosphere at around 310 to 620 mile (500 to 1,000 kilometers) above the Earth's surface.
In exosphere, molecules of hydrogen, atomic oxygen, helium, carbon dioxide, etc., are found. Here they are sparsely dispersed. Earth's gravity acts even on these molecules and the ions in the atmosphere and pulls them to it.
It is hard to define where the exosphere ends and the outer space starts. For this reason exosphere is taken to be a part of the outer space. However, scientists, at the theoretical level, consider that it extends up to 120,000 miles (190,000 kilometers). At this distance, atomic hydrogen velocities are more affected by the solar radiation than by the Earth's gravity. Geocorona is the glowing part of the exosphere and according to the reports filed by the Astrid satellites and the Galileo spacecraft which studied it from the outer space, it extends to more than 62,000 mile (100,000 kilometers) from the earth.
Altitude of Thermopause and Satellites
Satellites performing different functions occupy this layer as, here, they experience least resistance from the atmosphere. However, in this layer gas molecules concentrate at thermopause. The altitude and span of thermosphere and thermopause depends on how active the sun is. These satellites have a fixed orbit, and if the thermopause all of a sudden, shifts and engulfs to it, then the resistance experienced by the satellite, though it is not as big as that offered by the troposphere, is enough to affect its trajectory and make it fall to the Earth. The satellite monitoring stations on the Earth keep a constant watch on this, and change the orbits of their babies in the sky to avoid it.
Different atmosphere layers have different characteristics and roles. Each layer is important to man and is studied under the branch of Earth science. Sun blasts the Earth with the energy or heat in the form of infra-red radiations which atmospheric gases retains and reflects to the Earth. It helps the life on the Earth. Plants use it during the photosynthesis to produce food on which the organisms depend. However, the tremendous increase in the industrial activity is taking its toll on the atmosphere. Gases from different industries as well as those from the burning of fossil fuels are contaminating the atmosphere and increasing the green house effect. The earth has already witnessed the depletion of life-preserving Ozone layer. The temperature of the Earth is on the rise and according to some experts, by the middle of 21st century it will rise by 1.5 to 4.5º C from what it is today. It will melt the ice and will raise the sea levels creating a big problem for coastal areas and cities.