The earth’s atmosphere
The earth is surrounded by a layer of air, which is called the atmosphere. It reached to 560km from the surface of the earth, so we are only able to see what occurs fairly close to the ground. The atmosphere consists about 77% nitrogen , 21% oxygen, with traces of argon, carbon dioxide and water. The atmosphere of the earth can be divided into several distinct zones, as shown in the figure.The atmosphere is where all weather takes place; and extended from 8 to 14.5 km above the surface of the earth. The air pressure at the top of the troposphere is only 10% of that at sea level. Above the troposphere is the stratosphere and extend to 50 km, where air flow is mostly horizontal. The thin ozone layer in the upper stratosphere has a high concentration of ozone . this layer is primarily important as it absorbs the ultraviolet radiation from sunlight. The mesosphere is above the stratosphere and extends to 85 km. above the mesosphere is he thermisphere and extends to 600 km, where many atoms are ionized. The ionosphere is very thin, but it is where aurora takes place,and is also responsible for absorbing the most energetic photons from the sun. the exosphere starts at the top to the thermosphere and continues until it merges with interplanetary gases, or space.
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