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SAI INTERNATIONAL SCHOOL


             SUBJECT – GEOGRAPHY
             STD VII
             TOPIC- LESSON- 4-AIR
             SUB TOPIC- STRUCTURE OFATMOSPHERE

             NOTES-



                ÿ There are five layers within the atmosphere. The troposphere, the stratosphere,
                    mesosphere, ionosphere and exosphere are the layers of the atmosphere.
                ÿ TROPOSPHERE-The troposphere lies closest to the Earth and is about 13km thick. This
                    layer contains most of the air and oxygen in the atmosphere. Our weather is formed in
                    the troposphere.
                ÿ STRATOSPHERE-The stratosphere lies above the troposphere and goes up about
                    50km high. The ozone layer is in the stratosphere. The ozone protects us from harmful
                    rays from the Sun.
                ÿ MESOSPHERE-The mesosphere is the next layer, reaching 80 km from the Earth. The
                    mesosphere layer protects the planet Earth from the celestial rocky masses that enter
                    the atmospheric envelope of the Earth, where they burn as a result of their friction with
                    the air molecules and forming luminous meteors.
                ÿ THERMOSPHERE-It  is  the  layer  that  is located  between  the  mesosphere  and  the
                    exosphere. This layer is a layer that contains the charged ions, and it has an important
                    role in the wireless communications and broadcasting as it reflects the radio waves that
                    transmitted by the radio stations and the communication centres.
                ÿ EXOSPHERE-The  exosphere  is  the  outermost  layer  of  Earth’s  atmosphere. The
                    exosphere has gases like hydrogen and helium, but they are very spread out.
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