UNIVERSITY is composed of gases


NUMBER: SS/BSS/17/0376QUESTIONExplain the various atmospheric levels and indicate their various kilometres.ANSWERAtmosphere can be defined as an envelope or layers of gases surrounding the earth or another material body that is held in place by the gravity of that body. The atmosphere is composed of gases such as Nitrogen, Oxygen, Argon, water vapour and a number of trace gases.

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The earth atmosphere extends more than 560 Kilometres (348Miles) above the planet’s surface and is divided into layers which are the Exosphere, Thermosphere, Mesosphere, Stratosphere and Troposphere.The TroposphereThe troposphere is the lowest part of the atmosphere- the part we live in. it is the zone or layer where atmospheric turbulence and weather phenomena such as precipitation, rainbow, lighting and thunder are most marked. It contains 75 per cent of the total molecular mass of the atmosphere and virtually all of the water vapour (which forms clouds and rain).The troposphere starts at earth surface and goes up to a height of 7km to 20km (lowest toward the poles, highest in the tropics) above sea level. Throughout this layer, there is general decrease in temperature at a mean rate of 6.

5?C/km. The top of the troposphere is quite cold, the temperature there is around -55?C (-64?F) and warm at the bottom. This whole layer is capped by a temperature inversion layer, the tropopause, which act as a lid on the troposphere. Most types of clouds are formed in the troposphere.Figure1: Figure 1.above shows the various atmospheric levels and their various kilometres The StratosphereThis extends upwards from the tropopause to about 50 km. It contains much of the ozone in the atmosphere. In the stratosphere temperatures increase with altitude because of absorption of ultraviolet (UV) radiation from the sun by this ozone.

Temperatures in the stratosphere are highest over the summer pole, and lowest over the winter pole.By absorbing dangerous UV radiation, the ozone in the stratosphere protects us from skin cancer and other health damage. However chemicals (called CFCs) which were once used in refrigerators, spray cans and fire extinguishers have reduced the amount of ozone in the stratosphere, particularly at polar latitudes, leading to the so-called “Antarctic ozone hole”.The stratosphere contains only a small amount of water vapour (only about one per cent of total atmospheric water vapour) due to the “cold trap” and the tropopause, and vertical air motion in this layer is very slow. The stratopause, where temperatures peak at about -3°C, marks the top of the stratosphere.The MesosphereThe region above the stratopause is called the mesosphere and it begins from 50km above the stratopause and extends to about 80km- Here the temperature again decreases with height, reaching a minimum of about -90°C at the “mesopause” which is another zone of constant temperatures. It extends from 80km to about 93km above ground surface.

it separates the mesosphere from the next layer called the thermosphere. Meteors or rock fragments burns up in the mesophereThe Thermosphere and IonosphereThe thermosphere lies above the mesopause which extends from about 93km to about 500km and is a region in which temperatures again increase with height. This temperature increase is caused by the absorption of energetic ultraviolet and X-Ray radiation from the sun.The region of the atmosphere above about 80 km is also caused the “ionosphere”, since the energetic solar radiation knocks electrons off molecules and atoms, turning them into “ions” with a positive charge. The temperature of the thermosphere varies between night and day and between the seasons, as do the numbers of ions and electrons which are present.

The ionosphere reflects and absorbs radio waves, allowing us to receive shortwave radio broadcasts in New Zealand from other parts of the world.The ExosphereThe region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen atoms, but there are so few of them that they rarely collide – they follow “ballistic” trajectories under the influence of gravity, and some of them escape right out into space.The MagnetosphereThe earth behaves like a huge magnet. It traps electrons (negative charge) and protons (positive), concentrating them in two bands about 3,000 and 16,000 km above the globe – the Van Allen “radiation” belts.

This outer region surrounding the earth, where charged particles spiral along the magnetic field lines, is called the magnetosphere.REFERENCEwww.niwa. Acheampong, P.K 2016.

The Earth: Themes and Variation. University of Cape Coast.