NCERT Geography class 7 chapter-5

The envelope of air surrounding the earth is known as the atmosphere. Its exact thickness is unknown but the estimated upper limit is to be approx 10,000km from the mean sea level. The total weight of the Earth’s atmosphere is about 500 million tonnes. It is a mixture of gases whose amount varies from place to place and from time to time. Heavier gases like Oxygen are found in lower layers. Carbon dioxide absorbs heat and prevents the earth from getting too cold at night, known as the greenhouse effect. The increased level of carbon dioxide, carbon monoxide, etc leads to unusual heating of the Earth known as Global warming. The knowledge of the atmosphere is based on the information through radars and satellites. Troposphere- lowest layer and closest to the surface; temperature decreases with normal lapse rate; all-weather phenomena occur here; has about 90% of the air in the atmosphere. Stratosphere- estimated height is 50km above the mean sea level; free from all-weather phenomena; jet planes fly here; has Ozone layer; temperature remains constant till 20km height and then increases with increasing altitude. Mesosphere- height about 50–80km from mean sea level; temperature decreases with height; coldest atmospheric layer; meteors burn up in this layer. Thermosphere- height about 80–400km above mean sea level; temperature increases rapidly; low density of particles; has ionized molecules known as Ionosphere. Exosphere- outermost layer that ultimately merges to the outer space; a rarified form of gases; only has light gases like hydrogen and helium. The atmosphere is of great significance to the existence and survival of life on the planet Earth. For further information on the given topics please refer to my YouTube channel link- https://youtu.be/tz2Ar-pln9E