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The atmosphere The atmosphere is the air that surrounds the Earth. It extends upwards for hundreds of kilometres until it reaches space. Earth's atmosphere acts as a blanket. It is able to absorb heat as well as reflect some of the Sun's rays. This keeps the Earth's surface from getting too hot or too cold. If Earth did not have an atmosphere then it would look like the moon. The moon has no atmosphere and because of this is not protected from the extreme temperatures of space. On the moon the days are extremely hot, whilst the nights are freezing cold. As there is no atmosphere there is also no moisture, or water vapour, therefore no rain, snow or hail. No living thing can survive on the moon because there is no oxygen. The atmosphere is divided into five distinct layers that are: • the troposphere • the stratosphere • the mesosphere • the thermosphere • the exosphere. The atmosphere becomes thinner the further up you travel until it merges with space. All weather occurs in the troposphere, which is the layer of the atmosphere closest to the Earth's surface. It is very unstable in the troposphere layer of the atmosphere which is why aeroplanesfly at the top of this layer. If areoplanes flew in the trophosphere layer they would experience a lot of turbulence. Chapter 2: The Earth’s atmosphere The atmosphere is the air that surrounds the earth. Is made up of 4 layers: The Troposphere: Almost all weather and related processes take place here in the troposphere. The troposphere extends up to 17 kilometres above the Equator. Between the troposphere and the next layer, the stratosphere is the tropopause where temperatures are very low: about -40 celcius to -80 celcius. The air here is so cold that clouds are made up of ice crystals. The air within the troposphere is warmed by the heat that is radiated from the earth’s surface. We live in this layer The Stratosphere: The stratosphere extends about 50 kilometres above the earth’s surface. In the lower part of the stratosphere, temperatures are relatively constant and stable. However in the upper stratosphere temperatures increase up to 0 celcius at the top of the stratosphere due to the absorption of solar radiation. This section at the top of the stratosphere is known as the stratopause. It contains most of the atmosphere’s ozone. The ozone heats the air there by absorbing ultra violet rays from the sun. The Mesosphere: The mesosphere extends about 80 kilometres above the earth’s surface. Temperatures fall rapidly with elevation because there is no water vapour, cloud or dust to absorb incoming radiation. The lowest temperatures in the earth’s atmosphere occur at the top of the mesosphere called the mesopause. Temperatures get as low as -90 degrees celcius and wind speeds are as high as 3000 kilometres per hour, the strongest in the atmosphere. The Thermosphere: The thermosphere is the uppermost temperature region of Earth's atmosphere. The thermosphere is completely exposed to the sun’s radiation. The sun heats the extremely thin air to exceptionally high temperatures such as 1500 degrees celcius.