ATMOSPHERE An atmosphere (New Latin atmosphaera, created in the 17th century from Greek ἀτμός [atmos] "vapor"  and σφαῖρα [sphaira] "sphere"  ) is a layer ofgases that may surround a material body of suf ficient mass,  and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmospheres temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere.
LAYERS OF ATMOSPHERE The Troposphere The troposphere is where all weather takes place; it is the region of rising and falling packets of air. The air pressure at the top of the troposphere is only 10% of that at sea level (0.1 atmospheres). There is a thin buffer zone between the troposphere and the next layer called the tropopause.
STRATOSPHERE The Stratosphere and Ozone Layer Above the troposphere is the stratosphere, where air flow is mostly horizontal. The thin ozone layer in the upper stratosphere has a high concentration of ozone, a particularly reactive form of oxygen. This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. The formation of this layer is a delicate matter, since only when oxygen is produced in the atmosphere can an ozone layer form and prevent an intense flux of ultraviolet radiation from reaching the surface, where it is quite hazardous to the evolution of life. There is considerable recent concern that manmade flourocarbon compounds may be depleting the ozone layer, with dire future consequences for life on the Earth
MESOSPHERE The mesosphere (/ˈmɛs oʊs fɪ ər/; from Greek mesos = middle and sphaira = ball) is the layer of the Earths atmosphere that is directly above the stratosphere and directl y below the thermosphere . In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause , which can be the coldest naturall y occurring place on Earth with temperatures below 130 K. The exact upper and lower boundaries of the mesosphere vary with latitude and with season, but the lower boundary of the mesosphere is usually located at heights of about 50 km above the Earths surface and the mesopause is usually at heights near 100 km, except at middle and high latitudes in summer where it descends to heights of about 85 km. The stratos phere, mesosphere and lowest part of the thermosphere are collectively referred to as the "middle atmosphere", which spans heights from approxi matel y 10 to 100 km. The mesopause , at an altitude of 80 – 90 km (50–56 mi), separates the mesosphere from thether mos phere —the second-outermos t layer of the Earths atmosphere. This is also around the same altitude as the turbopause , below which different chemical species are well mixed due to turbulent eddies. Above this level the atmosphere becomes non -uni form; the scale heights of different chemical species differ by their molecular masses .
IONOSPHERE The ionosphere is a part of the upper atmosphere, from about 85 km (53 mi) to 600 km (370 mi) altitude, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.